. . . And Still We Evolve
A Handbook on the History of Modern Science
[This handbook, which has been prepared by Ian Johnston of Malaspina University-College, Nanaimo, BC (now Vancouver Island University), for Liberal Studies students, is in the public domain and may be used without charge and without permission, released May 2000]
[Table of Contents]
Section Three: The Origins of Evolutionary Theory
The Issue of Classification
To an extent unknown in the development of physics and astronomy, biology, the study of life, has always faced the great difficulty of dealing with an enormous diversity of phenomena, a world characterized by a bewildering range in the complexity, habits, and relationships among the objects of the inquiry. Central to the development of biology, therefore, has been the collection, observations, and, most important, classification of plants and animals (1).
The imperative need to create some system for organizing the huge number of observations in biology means that in following any narrative of historical developments in biology one needs to recognize from the start the crucial role played by the various attempts to classify the information, because systems of differentiating one group of phenomena from others directly shape the theoretical understanding of how such differences may have arisen. Systems of classification, in other words, are not ideologically neutral, not purely objective descriptions.
Obviously such systems must take into account more than simple similarities and differences among living things. There is also the most basic question about the difference between living and non-living phenomena. Common sense tells most of us what that difference is (although we may often be deceived), but comprehensive classification systems need to define what qualifies something to be included in the group of living things and, beyond that, to explore the relationship between living and non-living things. Can, for example, the former arise spontaneously from the latter? The answers to such questions play a crucial role in the construction of explanations.
To consider a simple but very powerful biological argument. If we separate all animals into two groups on the basis of whether or not individual members possess a backbone (i.e., if we establish two separate groups, the vertebrates and the invertebrates); if we further declare that all living creatures must have at least one living parent (i.e., there is no such thing as spontaneous generation of life from non-life); and if we finally determine that some members of the invertebrate group existed on earth long before the vertebrates ever appeared, then we necessarily conclude that the vertebrates must have arisen from the invertebrates (i.e., evolution with significant transformation must have taken place).
The force of this compelling argument (the best short simple proof for evolution) is the direct result of the system of classification adopted, the assumption about the creations of life, and the historical record of past animal populations. Without the initial classification system, the case would be impossible to make.
This example is meant to alert us to the way in which systems of classification in biology play a crucial role in shaping theoretical understanding of origins and relationships among different living things and, beyond that, carry important ideological implications. Classification systems are not simply convenient temporary rubrics; nor are they given from observation alone. Biologists create descriptive systems (taxonomies), and the rivalry between competing systems forms an important part of the history of the subject.
Moreover, given that a concept like evolution has ramifications far beyond the arguments among professional biologists, it is clear that classification systems have a direct bearing on a wide range of political, religious, and social issues. Few scientific concepts, in fact, have been more politically loaded than the various systems which scientists have devised to organize our understanding of the almost numberless varieties of life.
Early Classification Systems: The Great Chain of Being
The major early landmarks in the classical history of western biology were collections of observations. Aristotle’s (384-322 BC) History of Animals, Theophrastus’s (c. 381-276) De Plantis, and the Natural History of Pliny the Elder (AD 23-79) were primary sources of information throughout most of the middle ages about the habits and appearance of a limited number of animals.
Out of classical Greek philosophy, later Christian thinkers developed the most important classification metaphor for all forms of life, the Great Chain of Being, according to which everything in the universe exists in a carefully graded hierarchy from the inanimate material, through all forms of life, right up to God Himself.
The origins and development of this metaphor are complex. But the image appears to derive from two ideas in Plato’s Timaeus. First, God created the cosmos and everything in it because “He was good, and the good can never have any jealousy of anything. And being free from jealousy, he desired that all things should be as like himself as they could be.” Second, God created a huge variety of different life forms because “without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect” (29-30). This second idea (that God created all conceivable life forms because that was essential in a perfect creation), which was to play a very significant role in Christian theodicies and natural philosophy, is called The Principle of Plenitude.
Aristotle adopted a hierarchical arrangement in his classification system, his Ladder of Life (scala naturae), using complexity of structure and of function as fundamental criteria. Since the ladder or chain was to display an increasing vitality the higher the organism’s position, the capacity for motion was an important criterion for placement.
On the basis of these three Greek ideas, the goodness of God, the Principle of Plenitude, and the ladder of life, later Christian writers extended Aristotle’s classification system to organize the entire world of inanimate, animate, and spiritual being in a huge interconnected chain from the lowest inanimate stuff right up to God, a hierarchy in which the central principle determining rank was the spiritual worth (the soul) of the phenomenon. At the bottom of the scale was Hell itself (at the centre of the earth, the position furthest removed from God). Human beings occupied a series of intermediate positions, with the various ranks of celestial beings above them. Planetary orbits marked different stages in the angelic hierarchy. At the very top of the hierarchy was God.
Hence, the Great Chain of Being was, first and foremost, throughout the Middle Ages and the Renaissance, a theological and moral metaphor, establishing the divine structure of everything that is and reminding human beings about the pre-established hierarchy and harmony in the divine creation. The close connections between the Chain of Being and Ptolemaic astronomy, Dante’s cosmology, Hildegard’s art, medieval political theory, and Shakespeare’s poetic imagery, among other things, are clearly evident.
To understand the importance of this metaphor in the history of biology, two important characteristics need to be stressed. First, the various ranks in the chain were fixed. There was no mobility from one rank to the next. In fact, for human beings, forgetting one’s position on the chain was a great sin, for it led people to behave either like the life forms below (the animals) or to aspire to a condition above their divinely appointed station. This was a manifestation of pride, the most dangerous of all Christian sins. Secondly, the hierarchy was complete and closed. All forms of life had been created in the beginning, and there was no room for new life to appear. The arguments to support this latter point were drawn from Plato’s original Principle of Plenitude and from Genesis. The differences between distinct positions on the scale were not major, for every creature bore many resemblances to the life forms above and below. This was the origin of the famous saying (much quoted by Darwin): natura non facit saltum (nature does not make leaps).
The Great Chain of Being was an extraordinarily important classification system, providing a complete and coherent structure for all natural and spiritual phenomena in an easily comprehensible order. It is one of the longest lasting and most influential metaphors in the history of ideas, and its impact on natural science has been central, “the greatest synthetic scheme in pre-Darwinian biology” (2).
The idea was still the major organizing principle for biology in the 17th and 18th centuries. And natural theologians could invoke the metaphor as part of the argument from design to celebrate this fixed but scrupulously organized world as the best of all possible arrangements:
From the supposition of a Scale of Beings, gradually descending from perfection to nonentity, and complete in every intermediate ranks and degree, we shall soon see the absurdity of such questions as these, Why was not man made more perfect? Why are not his faculties equal to those of angels? Since this is only asking why he was not placed in a different class of beings, when at the same time all other classes are supposed to be full. (Law)
Classical Theories of the Nature and Origin of Species
Central to any system of classification, of course, was a proper means for distinguishing different groups or types of living things (i.e., an analytical principle of identifying similarities and differences). And any system proposing such divisions implicitly raised the problem of where these divisions originated. Were the different groups created by the classification system real (i.e., based on the truth about nature) or artificial (i.e., convenient human creations)?
The classical basis for dealing with such questions was Plato’s theory of forms, which addressed both the definitions of species and theories of origin. According to Plato, the forms were the real, ideal, and archetypal life forms (horse, tree, human being). The objects on the earth which we perceived were less real (because they were subject to change). Members of the same species on earth were all somewhat different, because their relationship with that ideal form was not perfect. Plato was ambiguous about the relationship between the ideal reality (which could not be perceived but could be imaginatively apprehended by a few specially trained intelligent people) and the objects of sense experience, sometimes using the metaphor of imitation and at other times using the metaphor of participation. Moreover, since these ideal forms were also the creative source from which everything arose, Plato’s theory served both to classify and to explain the origin of the different forms of life.
Aristotle similarly saw forms as the first principles of origin, but he located them in the individual living organisms. A living being was created in the generation of the individual form from its parents, but this perpetuated and did not originate the species. The form struggled to manifest itself against recalcitrant matter (this accounted for the variations within a species).
Medieval writers drew on this Greek tradition to maintain the Genesis view that God was the origin of all things, including the various species, all of which He had created together according to the Biblical account in Genesis. To explain the process, for example, St. Thomas Aquinas (1125-1274) maintained the Platonic traditions in the Timaeus (concerning the goodness of God and the principle of plenitude) and Aristotle’s sense of forms inhering in matter. During the six days of Creation, God set into matter all the inherent forms (i.e., the number of species was at that time fixed) and created the structure embodied in the Great Chain of Being.
The Development of New Systems
Traditionally, then, the question of the origin of life was linked directly to God’s creation, as described in Genesis. It involved at that time the fixing of all species. As mentioned earlier, the Great Chain of Being was not a developing or evolving hierarchy. And it was fully complete. Thus, there was no room for the emergence of new species.
In the 17th and 18th centuries, this notion, which had not been seriously challenged since its inception and which had been for centuries an ideological mainstay of those defending traditional order, was both undermined by different approaches to the question of the earth’s development and defended or adapted by various means (scriptural and scientific). Not unexpectedly, this tension between a long-established conception and new theories of classification generated some fierce disputes.
A major part of the pressure to create new classification systems, more immediately useful than the traditional Great Chain of Being, came in the 16th and 17th centuries from the rapidly accelerating accumulation of information about the natural world. The overseas explorations, the growth of interest in fossils, and the remarkable discoveries of the first generation of scientists using the microscope (in the second half of the 17th century) were providing an enormously rich amount of complex information. There was thus a growing need to introduce into natural history organization systems which could make sense of the mountains of descriptive details. By the year 1600 about 6000 plant species were known; by the year 1700 about 12,000 more had been added.
The desire to construct useful classification systems immediately raised two important questions about what one should select as the basis for identifying similarities and differences. Should one, for example, select some similarity in the life cycle (perhaps following Aristotle by making, in the case of sexually reproducing organisms, the production of fertile offspring the criterion for belonging to the same group). Or, alternatively, should the basis for similarities and differences be certain structural features and, if so, how many should one include? The question of structure was increasingly difficult because of the growing evidence from microscopic studies of the amazing complexity of organic life.
The attempts to deal with such questions focused attention on two different approaches to distinguishing the different forms of life. A natural system of classification tried to base itself on all the observed resemblances between similar living things (or as many as possible), taking into account all known characteristics (different values being ascribed to different features according to their presumed importance). The crucial but very difficult task was to take into account as many of the organism’s features as possible. An artificial system of classification, by contrast, based itself, for the sake of making the classification easier (or even possible), on the selection of a very few particulars, assessed independently of other features of the living organisms (3).
Early attempts at new classification systems in the 17th century were essentially artificial. The Fleming Matthais de l’Obel (1538-1616), for example, botanist to James I of England, grouped plants on the basis of their leaf structure; Andrea Cesalpino (1519-1603), professor at Pisa, arranged plants by the flowers and fruits, as did the Swiss Kaspar Bauhin (1560-1624) and the German botanist Joachim Jung (1587-1657).
From the work of these early modern botanists emerged a more precise idea that the larger groups of plants, those which bred true to form, that is, produced offspring of the same general type (what we call species) divided naturally into a number smaller groups (what we now call varieties). Out of this knowledge arose, somewhat imperfectly, especially in the work of Bauhin, a system of binary classification (now called binary nomenclature), the first name indicating the species and the second the variety.
John Ray and Carl Linnaeus
One of the greatest of the early pioneers in this effort to produce a new systematic knowledge of plants and animals was John Ray (1627-1705), an English naturalist, who produced a catalogue of the plants of the British Isles (1667) and a later one for birds (1656). Ray, along with Linnaeus (see below), is considered the chief founder of modern systematic biology.
Ray’s greatest work was Historia generalis plantarum in three volumes, 1686-1704, an encyclopedic study of the structure, distribution, and habits of plants. He arranged into 126 sections (or Natural Orders) about 18,600 plants. His system, like those of his predecessors, was artificial. For example, in distinguishing plant species Ray placed particular emphasis on the structure and development of the flower.
Ray’s study of animals (published in 1693) was the first modern systemic classification. He began by distinguishing animals with hooves from those with nails; the former he then classified according to the structure of the hoof (single, double, quadruple). The double-hoofed animals were then further subdivided into those that chewed the cud and those that did not. The second major group (animals with nails) Ray subdivided on the basis of their toe structure.
The result of Ray’s classification of animals was a scheme which contained ten different species: horses and asses; cattle and sheep, deer, pigs, rhinoceros and hippopotamus, camel, elephant, dog and cat, rabbit and beaver, and those of human form (like monkeys) (4).
Carl Linnaeus (1707-1778), a Swedish natural philosopher, like John Ray, set himself the task of constructing a new Aristotelian classification system for plants and animals. His classic work System of Nature was first published in Holland in 1735. The book succeeded in assigning a descriptive place to every known animal and plant in a comprehensive system of classification, similar in many respects to the one still followed today. The book is justly celebrated as one of the greatest works in the history of biology.
Linnaeus’s system involved placing the organism first in a Class, then in an Order, then in a Genus, then in a Species, and finally in a Variety. The division of plants was an artificial one, based on structural features of the plant’s reproductive system (the number of stamens, or free male parts, was the foundation of the division of classes; the female parts were the basis for division into orders).
For the animals Linnaeus distinguished six classes: Mammals, Birds, Reptiles, Fish, Insects, and Worms (the last two included all animals without vertebrae). The basis for the distinctions between the vertebrates was the structure of the heart, the nature of the blood, the form of birth, and respiration (i.e., a more natural classification, taking into account a great many structures).
Linnaeus placed no great emphasis on historical cosmological or pre-evolutionary theories (already circulating in his own time). His central interest was always in systematic taxomony, based on the idea of the permanence of species. However, after his initial claims that there were now as many species as God had originally created (“There is no such thing as a new species”), Linnaeus did later speculate that there might be now many more species than God had made in the first weeks because new species had arisen from cross breeding in plants (5).
The Growth of Historical Accounts
Ray and Linnaeus both adhered to the idea, derived from the Great Chain of Being, of the eternal fixity of the design in nature which their classification systems revealed. Ray wrote in his Wisdom of God Manifested in the Works of His Creation (1691) of the evidence in fossils for extinction, but he did not advance a theory of historical development and change. Thus, any evolutionary potential in his system (e.g., the category of animals like human beings) remained buried, and the old idea of fixity of species was not challenged.
The concept of fixity of species, like Newton’s unchanging cosmology, obviously did not encourage a historical narration of the earth’s development. But growing evidence from geology and from the newly emerging science of embryology (which was revealing more and more about the development of the fetus) made the issue increasingly complex and put pressure on those who would defend traditional ideas to come with more satisfactory explanations.
One attempt to defend the static view on the question of species was the work of William Whiston (1667-1752), who maintained that the production of animals and plants, and thus the creation of species, was beyond natural law. According to Whiston, God had, at the time of the Creation, formed all the organisms that were ever to live on the earth: the original members of each species contained encapsulated, in an arrangement resembling boxes within boxes (like pre-existent germs), all future members of that species. This doctrine is called preformation, a concept discussed further below.
The first great modern natural philosopher directly to challenge the notion of fixity of species and to propose that species were not permanent was the French scientist mentioned in Section Two, Georges Louis Leclerc, Comte de Buffon (1707-1788), whose Histoire Naturelle (in forty-four volumes published over a fifty-five year period from 1749 to 1804) attempted to present an all-inclusive account of science.
Buffon had little interest in the precise details of systematic taxonomy, of the sort offered by Ray and Linnaeus. He sought rather the unity of living things and thus fastened on the phenomenon of reproduction as central to an organized biological theory. Lacking any specific empirical knowledge of the cellular basis for sexual reproduction (which had not yet been discovered in any detail) Buffon proposed the idea of organic molecules and matter combining to form an internal mold, in the process of reproduction, a “constellation of active, penetrating forces, analogous to gravitational force.”
Buffon, in fact, was much more interested in such dynamic processes of life (and of the earth, as we have seen in Section Two) and in the possibility of discovering some overarching natural law to account for them than he was in the empirical descriptive work of classification on the basis of a notion of an eternally static creation. As a result, his work marked a significant shift away from an emphasis on the permanence of species and towards a view of nature based on constant process.
Buffon went so far as to insist that the very notion of species was nothing more than nominalism (i.e., species were artificial categories created for human convenience, just words, without any correspondence to nature), for such groups had no permanent reality. Thus, his concept of biology differed fundamentally from Linnaeus’s work, which was based on a belief that classification into distinct species corresponded to real and permanent divisions in organic life.
What is particularly significant about Buffon’s notion of species is that he viewed the concept historically, as a matter of lineage (rather than as an eternally present abstract “class”). To understand species properly, according to Buffon, one had to trace the history and distribution of its members:
It is neither the number nor the collection of similar individuals which forms the species. It is the constant succession and uninterrupted renewal of these individuals which comprise it. . . . The species is thus an abstract and general term, for which the thing exists only in considering Nature in the succession of time, and in the constant destruction and renewal of creatures. . . . (1753)
Moreover, species, in Buffon’s view, were not eternally fixed; rather, in a break with the long Aristotelian tradition and with one of the most central features of the Great Chain of Being metaphor, he proposed that animals altered in type occasionally, sometimes retaining features of their previous type:
. . . the pig is not formed on an original perfect plan, since it is a compound of other animals. It has parts which can never come into action, as lateral toes, the bones of which are perfect, yet useless.
Some species, he argued, were debased versions of others: the ape, for example, was a degraded human being, and the ass was a degraded horse.
Moreover, the active molecular process at the heart of reproduction, according to Buffon, had caused the higher animal life forms. There was no gradual evolution. Variations in species did occur under the influence of the changes in the earth’s geology (particularly the shifts in temperature: the elephant, for example, had grown smaller as the earth had cooled).
Buffon’s notions of historical process in natural history, as we have seen in Section Two, got him into difficulties with orthodox traditional opinion. This is not surprising, for in biology, even more so than in geology, ideas of change as an inherent part of the historical natural order (even those based, like Buffon’s, on degeneration) were ideologically suspect to those with a vested interest in the existing social and political order.
Linnaeus’s and Buffon’s programmes represent two different conceptual approaches to natural history--the former stressing classification and the construction of a comprehensive descriptive system, the latter stressing the importance of narrative (historical) accounts, genealogies, in the understanding of living organisms.
This distinction between a descriptive taxonomy of nature and an interrelated history of nature was addressed by Kant in his course on physical geography (1775) and in his paper “On the Different Races of Men” (1775):
The logical division [of nature] proceeds by classes according to similarities; the natural division considers them according to the stem, and divides animals according to genealogy, and with reference to reproduction. One produces an arbitrary system for the memory, the other a natural system for the understanding. The first has only the intention of bringing creation under titles; the second intends to bring it under laws.
This distinction, especially with Kant’s emphasis on the contribution of historical biology to the development of laws, was to provide in Germany a considerable incentive to the efforts of the Naturphilosphen to explore the historical development of organisms by seeking out similarities and speculating about common ancestors for different species (more on this below).
In England, one of Buffon’s most enthusiastic readers was Erasmus Darwin (1731-1802), grandfather of Charles Darwin, whose four-volume work Zoonomia: Or the Laws of Organic Life (1794-1796) proposed that all the remarkable changes that species undergo are due to influences which come from inside and outside the organism and which are then passed (by some physiological vitalist principle) to the offspring, a doctrine which later came to be called the inheritance of acquired characteristics.
From their first rudiment, or primordium to the termination of their lives, all animals undergo perpetual transformations; which are in part produced by their own exertions in consequence of their desires and aversions, of their pleasures and their pains, or of irritations, or of associations; and many of these acquired forms or propensities are transmitted to their posterity.
As a doctor, Erasmus Darwin was particularly interested in the hereditary transmission of disease and of certain physical ailments, like alcoholism, stammering, and sea sickness and in the social implications of such transmissions: “As many families become gradually extinct by hereditary diseases . . . . it is often hazardous to marry an heiress, as she is not unfrequently the last of a diseased family.”
In his last work, The Temple of Nature, posthumously published in 1803, Erasmus Darwin organized the entire poem around the concept of evolution as a huge all-inclusive process by which mechanistic irritation triggered the life force, thus initiating a process of development. This, in turn, launched a pattern of progress, one which stressed the importance of inner energy and drives, the need to learn, and the adaptability of the individual. Though Darwin invoked mechanical principles, the final vision saw the human being not as a machine but as a creature that could realize a certain potential for change and could pass on such changes (or some of them) to the next generation (6).
Forces of Life: Mechanical or Vital?
Central to the arguments between those maintaining the fixity of species and those exploring a more dynamic historical process as the basis for natural history was the complex and ancient problem of the nature of life itself, a question which was becoming increasingly pressing in the mid-18th century. Where did life come from? What maintained life? If one wanted to argue about the origins of life (or of particular species) how was one to understand the processes that separate living from non-living phenomena?
Such questions were fundamental in these arguments, because, as the pressure intensified to suggest links between one species with another (by some form of transmutation or change) or to posit the emergence of new species, the issues concerning reproduction and embryo development moved to the centre of scientific debate.
Historians of science have characteristically distinguished two recurring groups of answers to such basic questions: the mechanistic and the vitalistic. This division corresponds roughly to that between those who believe that the best answers are to be found in mechanistic physical science (atoms, chemicals, and the laws of nature) and those who find such a response reductionist and who thus search for an explanation in terms of some non-mechanical power or force inherent in living organisms (just what that inherent force might be has been the source of many differences among vitalists) (7).
In the period from the 17th to the 19th centuries, both mechanistic and vitalistic theories flourished. Descartes, as we know, encouraged the view that animals were to be viewed simply as complex machines entirely governed by mechanical processes, but the enormous difficulty of finding mechanical analogues for much animal behaviour (together with a certain opposition to what was seen as the reductionism of such explanations) encouraged vitalist alternatives to Cartesian and Newtonian systems (8).
It would be a mistake immediately to conclude that mechanistic science committed itself to opposing religion, whereas vitalist science strove to support religious views. While that distinction sometimes held, many of the most prominent mechanist natural philosophers were devout Christians, and many vitalist theories offended orthodox theology considerably. David Hume, for example, proposed a vitalistic principle of order inherent in the universe, with no particular theistic meaning, and some of the Romantics were eager exponents of a heretical vitalistic pantheism. Moreover, mechanical principles were as often as not invoked by natural theologians to argue for a spontaneously progressive evolution.
Associated with these concerns was the idea that certain living things could, under specific conditions, arise spontaneously from non-living matter (e.g., from generative slime or dung), a notion centuries older than Aristotle. Evidence for such a process seemed abundantly clear from the appearance of dung beetles in animal droppings, maggots in dead meat, fermentation, and intestinal worms, among other phenomena.
Spontaneous generation was not significantly challenged until the 17th century, when Francesco Redi of Florence (1621-1697) concluded by simple experiments which involved comparing meat exposed to the air with meat sealed off from the air, that “the flesh of dead animals cannot engender worms unless the eggs of the living be deposited therein.” However, in 1748, John Needham, an English Catholic priest, repeated Redi’s experiments under much more stringent conditions but came to the opposite conclusion, based on his observations of the growing presence of microscopic animalcules in mutton broth “as good as hermetically sealed.” Needham’s work fueled an energetic debate about spontaneous generations (with many different experimenters testing the hypothesis), but the issue was not finally settled until the work of Louis Pasteur (1822-1895), who in 1861 demonstrated that fermentation and infection were the result of air-borne organisms (9).
These facts should remind us that the energetic (often vitriolic) arguments about classification, transmutation, evolution, and speciation which characterized biology in the late 18th and 19th centuries, as the historical view challenged the older notion of the fixity of species, were conducted without a thorough knowledge of some of the issues most basic to the debates. For example, the precise role of the parents in reproduction was for a long time unclear (10).
Particularly vexing, too, were the questions arising from the development of the embryo. How did it grow? What guided its growth? Generally speaking in the late 17th and early 18th century there were two forms of answer to the problems of reproduction and embryo growth. The first one, derived from Aristotle and endorsed by William Harvey, is commonly called epigenesis. In this theory, the embryo developed from a mixture of the parental sexual material and grew over time from something quite simple into something more complex, by an as yet unknown vitalistic process (i.e., the embryo went through a series of significant stages).
The second view was the theory of preformation, which maintained that the embryo existed in some preformed state within the parent and, rather than evolving through significantly different stages, simply grew bigger. Variations, in this view were the product of the embryo’s environment.
One important attraction of the preformation theory was that it was much more amenable to mechanistic biology, since it was impossible to explain an evolving embryo with an analogy to a mechanical process. If one wished to avoid appeals to vitalist principles, then the preformist hypothesis made more sense. In addition, the preformist theory fit certain observations about embryos. The famous Swiss physiologist Albrecht von Haller (1708-1777) was struck by the fact that in the embryo the organs functioned as soon as they were visible. Assuming that all bodily organs were mutually independent, he reasonably concluded that all organs were present from the start. In addition, of course, the preformist explanation was much easier to reconcile with the doctrine of the fixity of species. With each generation contained in the seed of its ancestors, the origin of new species would be hard to imagine.
The prefomist hypothesis opened up a debate about which parent’s seed contained the preformed embryo. There were objections to locating it in the sperm, since this necessitated a great loss of life in the reproductive process. When the ovum became the preferred site for the preformed embryo, some argued that the spermatozoa were in no way essential to conception but were, in fact, small parasites. The preformist hypothesis was very difficult to disprove, since its adherents, like von Haller, could always meet objections which pointed to the growth of the embryo from something very small by arguing that the preformed seed was simply present in too minuscule a form to be detected.
An obvious objection to the doctrine of preformation was the existence of significant abnormalities from parent to offspring. For example, the French physicist and philosopher Maupertuis (1698-1759) attacked preformation and postulated (on the basis of his observations of an albino Negro boy shown all around Paris in 1744) that each sex contributed particles drawn from all over the body (an ancient Greek notion, apparently first proposed in a rudimentary form by Pythagoras). Conception occurred when similar particles came together in the uterus to construct the organs of the offspring.
Could one not explain by that means how from two individual alone the multiplication of the most dissimilar species could have followed? They could have owed their first origination only to certain fortuitous productions, in which the elementary particles failed to retain the order they possessed in the father and mother animals; each degree of error would have produced a new species and by reason of repeated deviation would have arrived at the infinite diversity of animals that we see today.
At the time Maupertuis’s ideas were little more than an extravagant speculation, since he brought to bear very little detailed evidence and had to appeal to an inexplicable force, analogous to gravitation, to assemble and coordinate the various seminal particles. It is interesting, however, (and not too Whiggish) to note that he did see the importance of the origin and transmission of variations in constant changes in the sexual material contributed by the parents.
Epigenesis, the hypothesis that the embryo grew from a simple to a much more complex organism, appeared to suggest a progressive evolutionary development. In fact, the term evolution was commonly first applied to the development of the embryo through distinctly different stages.
This brief excursion into embryology should remind us that, in the absence of any detailed knowledge of the cellular basis of sexual reproduction and genetics, many of the most pressing questions could not be resolved satisfactorily, by Darwin or anyone else. Only in this century have we been able largely to agree on many previously divisive issues, thanks to the rapid progress in microbiology.
Transmutation of Species
Speculation about the ability of species to change (transmutation), of the sort undertaken by Maupertuis, was commonplace in the 18th century. The appearance of new species of plants through cross breeding (a very old practice in farming), the practices of domestic breeders of animals, the changes undergone by an embryo, and other factors led a number of natural philosophers to propose that species must be, in some manner, mutable.
Buffon (1707-1788), as we have seen, proposed a theory of “degeneration” by which new variations could develop as a falling away from some earlier type of animal into a new form. Recognizing that life reproduced faster than the food supply, Buffon further proposed a struggle for existence on the part of all living things:
Nature turns upon two steady pivots, unlimited fecundity which she has given to all species; and those innumerable causes of destruction which reduce the product of this fecundity.
Such “anticipations” of Darwin’s later theory are scattered throughout Buffon’s vast work Histoire naturelle (1749-1804) (11).
Another very prominent French scientist, Georges Cuvier (1769-1832), whose nickname “the dictator of biology” indicates his power and influence in French science early in the 19th century, strongly opposed Buffon’s notion that species were mutable (12). Apart from the lack of sufficient fossil evidence for such a process, for Cuvier the idea that each species was a perfectly harmonious and very complicated combination of interdependent structures meant that isolated variations would lead to immediate extinction. This idea is called the Principle of Correlation of Parts, and it is still a common objection to Darwinian natural selection. For evolution to occur, in Cuvier’s view, the changes would have to be enormous, including virtually the entire structure of the animal (13).
In addition, Cuvier was, like Linnaeus, a taxonomist (a builder of systematic classification systems) and, as such, not inclined to welcome theories of built-in change, especially from someone like Buffon, who denied the reality of the concept of species. Cuvier’s research led him to conclude that there had been several stages to the earth’s history (defined by various catastrophes), but he held firm to the notion that since the last great flood (which he dated at roughly the same period as the Biblical account), animal life on earth had remained unchanged. The last Creation had thus fixed the species into permanent categories (14).
Cuvier developed a system of classification for comparative anatomy quite different from what had been offered previously. He divided animal life into four major division: vertebrates, mollusks (snails, cuttlefish), articulates (insects, crustaceans), and radiates (starfish). Further, he insisted that the similarities within each division were based, not on any overall plan, but solely on similarity of structure due to similar functional needs. The different divisions were characterized chiefly by their nervous systems, and these were so distinct in each group that there was, in effect, a huge gap between each of them, with no intermediate types (no linking species between the major groups).
The implications of this classification system were profound. For it emphatically denied any overall natural unity of plan or higher law which might constrain God in His design of animals. God acted in nature to adapt and harmonize the structure of animals’ interdependent organs so as to meet functional requirements (the relevance of this approach to the argument from design is evident). The scientist’s job was not to pursue inquiries into sweeping universal laws, but rather to study closely particular functional structures, to, in Bacon’s terms, follow the role of the ant rather than that of the spider, leaving aside questions of overall purpose.
The great strength of Cuvier’s theory was its emphasis on close and careful empirical studies of organic structures. He was one of the first to insist that the collection of fossils needed to be closely linked to the placement of rocks from which they came, so that the study of life in the past ages of the earth could be based upon reliable field evidence. But he was deliberately hostile to grand biological theory, of the sort encouraged by Buffon and the Enlightenment interest in general laws of nature. This feature of this thinking made his biology particularly attractive to conservative ideology, which by the end of the 18th century and for much of the 19th was striving to meet the challenges of evolutionary biology, particularly in its materialistic forms.
Hence, Cuvier and his brilliant English colleague, Richard Owen (1804-1892) became leading establishment figures in the heated political and scientific disputes between conservatives and radicals in the first three decades of the 19th century.
As we have seen in Section Two of this handbook, the pressure to examine the earth historically as subject to a unique process of change over time came, not from physics or from studies of embryos, but from geology. And in that new science, the matter of most urgent interest to biologists concerned with question about species was the growing knowledge about fossils.
The evidence of extinction (which accumulated with the increasing evidence of large animal remains) challenged the old argument that God had created all possible creatures in a manner preadapted to life on earth. However, by appealing to the idea that the earth’s environment had changed from time to time (a matter which was becoming overwhelmingly clear from the work of the geologists and paleontologists, especially Cuvier), one could still preserve the principle of plenitude by claiming that God had pre-adapted a maximum number of species to flourish in each successive but transient environment.
The fossil record presented problems to those defending the fixity of species because the evidence pointed increasingly to a wide variety in the complexity, distribution, and types of fossils in different rock layers, with more complex and more frequent remains in the younger layers.
Not surprisingly, then, certain speculative evolutionary systems were, as we have seen, proposed, in geology and in biology (15). But the main credit for anything approaching a modern evolutionary system is normally given to Jean Baptiste de Money Lamarck (1744-1829), a French botanist and, later, zoologist, in the Jardin du Roi and a colleague of Cuvier’s. Lamarck was the first to use the term Biology (in 1802) to refer to both fields of inquiry. Lamarck’s major work, Philosophie zoologique came out in 1809.
Larmack was moved to propose his evolutionary theory on the basis of his observations that the difficulty of distinguishing between varieties made it improbable that any species could be permanently fixed. All the different types of dogs, Lamarck speculated, must have had a common ancestor. His knowledge of the work of domestic breeders led him to suggest that the source of the variations which breeders recognized must be also operative in nature. Something in the environment, Lamarck concluded, must be constantly creating variations.
Species, Lamarck argued, could only remain fixed if their environment remained unchanged. Since there was compelling evidence that nature was constantly changing, then species must also have altered under this environmental pressure. Such changes individual animals passed onto their offspring, so that new features developed in the lifetime of an individual animal would be preserved. This famous doctrine, as mentioned above (in the discussion of Erasmus Darwin) is called the Inheritance of Acquired Characteristics.
Central to Lamarck’s theory of transmutation was the notion of use and disuse. Changes in the environment led to special demands on particular morphological features (like the neck on the giraffe, which had to extended itself to reach scarce vegetation). An inner force inside the organism initiated a mechanical process of change within the living creature, and this change was transmitted to the next generation:
Every new need, necessitating new actions to satisfy it, requires of the animal that it either (a) use certain parts more frequently than it did before, thereby considerably developing and enlarging them, or (b) use new parts, which their (new) needs have imperceptibly developed in them, by virtue of the operations of their own inner sense.
Lamarck also proposed an inherently progressive element in transformation, so that with time organisms increased in complexity and rose gradually towards perfection. The metaphor of a single great chain was implicit in his entire system, but it was now a mobile hierarchy, with agents possessing an inner drive to ascend. Furthermore, the process of ascent could be constantly restarted at any time by spontaneous generation.
As one might expect, Lamarck’s radical theory got a very hostile reception from Cuvier and from the French and English scientific establishment, for his biology turned life from an eternally fixed pattern to a ceaselessly dynamic process of change. The critics were quick to point out the lack of key evidence (as they were with Darwin fifty years later). Lyell, for example, rejected Lamarck’s doctrine on the ground that
. . . if we look for some of those essential changes which would be required to lend even the semblance of a foundation for the theory of Lamarck, respecting the growth of new organs and the gradual obliteration of others, we find nothing of the kind. (16)
Lamarck died blind and in poverty at the age of eight-five. Cuvier’s eulogy to Lamarck was predictably hostile, and his most obvious heir, Charles Darwin, did not seem to entertain a very high opinion of Lamarck’s work. Even now, Lamarck is still remembered mainly for the widely discredited theory of the inheritance of acquired characteristics (a belief which he did not originate and to which Darwin also subscribed), rather than celebrated as one of the first to propose a comprehensive theory of evolution (17).
The discredit heaped on Lamarck in respectable English circles may have had an influence on Darwin’s decision to delay the publication and to limit the scope of the Origin of Species, which, as is often observed, has only one sentence about human beings in it: “Much light will be thrown on the origin of man and his history” (18).
In his own age, Lamarck’s theories at first attracted little following, but by the second decade of the 19th century they had gained great support from Etienne Geoffroy Saint-Hilaire, a zoology professor at the Museum, who emerged in France and in England as the chief opponent to the more conservative biology of Cuvier and Owen (19).
Geoffroy developed a biology significantly different from Cuvier’s, something much more in the spirit of Buffon. He denied the importance of function in determining structure and sought instead for the resemblances between similar organs (irrespective of function). In other words, he looked for homologies (for example, the similar bone structure in the wing of a bird and the fore legs of a mammal) (20). Thus, where Cuvier insisted on the absolute dichotomies between animal groups, Geoffroy stressed their comprehensive unity of plan. For Geoffroy the scientist’s task was to seek out these homologies, the evidence for an overall unity of structure, and so arrive at an understanding of the higher laws governing all animal life, natural rules which had nothing to do with function and everything to do with unity of composition.
The differences between Geoffroy’s and Cuvier’s theories derived essentially from the conflict between the 18th century Enlightenment spirit for unifying general laws (of the sort Newton had provided) and the traditional notions of permanent separation and subordination in natural order. Thus, the two different approaches to organizing knowledge about animals prompted fundamentally different ways of understanding the role of the anatomist, the meaning of anatomical evidence, and, beyond that, of the social implications of biology.
Geoffroy’s scheme meshed well enough with Lamarck’s concept of evolution and transmutation to form a thoroughly radical and secular biology--in England called philosophical anatomy--based on laws of nature controlling form and stressing the importance of the environment and a dynamic relationship between animals of very different types. The doctrine of homologies encouraged thinking about common ancestors from which present species might have descended, something which reinforced Lamarck’s theory of constant change. This new “republican biology” set itself against any traditional argument from design in favour of promoting the ideas of constant development and spontaneously generated process (progress from below) according to natural law.
The radical political dimensions of this biology were well brought out in William Lawrence’s Natural History of Man (1819). Lawrence, a reform-minded surgeon, posited that racial differences had been produced by heredity and that better breeding in human beings was a necessary step in improving the corrupt and mentally deficient aristocracy. The book caused a scandal and was banned; overnight Lawrence became a leading figure in the radical press (later, like so many English radicals, he recanted, became president of the Royal College of Surgeons, and accepted a baronetcy from Queen Victoria).
One well-known doctrine which Geoffroy’s and Lamarck’s new philosophical anatomy fostered was that of a common law in embryonic development, one in which the embryo passed through a series of stages corresponding to the stages undergone by the species in the history of its development. In 1821, a German biologist J. F. Meckel (1761-1833) formulated this principle of embryonic development in the “law of parallelism” or recapitulation: the embryo’s growth took it through a hierarchy of ascending forms, from the lowest to the highest levels of organization. Lower animals were thus immature versions of human beings. This idea roughly coincided with the awareness among paleontologists that the sequence fish, reptiles, mammals corresponded to the sequence in which the animal orders had appeared on earth.
In England Robert Chambers introduced such an evolutionary principle, arguing in Vestiges of Creation (1844) that “each animal passes, in the course of its germinal history, through a series of changes resembling the permanent forms of the various orders of animals inferior to it in the scale.” As for human beings, their “organization gradually passes through conditions generally resembling a fish, a reptile, a bird, and the lower mammalia, before it attains its specific maturity” (21).
Chambers also offered a mechanical cause for the production of higher forms (something Lamarck had failed to address, except by an appeal to some ambiguous quasi-vitalist striving). Since monsters were caused by arrested fetal development, Chambers reasoned, the creation of higher forms
has never been anything more than a new stage of progress in gestation, an event as simply natural, and attended as little by any circumstances of a wonderful or startling kind, as the silent advance of an ordinary mother from one week to another of her pregnancy.
Thus, an alteration in the period of pregnancy would lead to the production of higher forms of life. Chamber’s book was denounced in the reviews (not least of all because the subject matter, fetuses and pregnancy, was, in some people’s minds, unfit for “our glorious maidens and matrons” who should not soil their thoughts with “the dirty knife of the anatomist”). But Vestiges was extremely popular, even sensational (as Chambers, who published it anonymously, hoped it would be) in the decade before the Origin of Species first appeared (Darwin himself refers to the book in the opening paragraphs of his argument) (22).
The political implications of the influence of the new materialistic evolutionary science from France and elsewhere were clear in England. By 1833 the medical establishment was complaining about “laws of medical science [based on] truth and reason [being] universal and republican.” The debate in the 1830’s between the followers of Cuvier and Owen and those of Lamarck and Geoffroy is one of the great arguments in the history of biology. At the centre of the conflict was the question whether human beings should be subordinated to an autonomous, lawful, transforming, and materialistic nature (as the philosophical anatomists maintained) or whether their place in nature was incomprehensible without appeal to God and His set designs (as Cuvier insisted).
What made this debate all the more fascinating (apart from the stormy political dimension) was the constant supply of new evidence for the disputants to consider and the keenness with which anatomical issues were discussed. New fossils, strange animals from the new world, and fresh studies of embryos fostered rich international scientific arguments. The philosophical anatomists tried to break down Cuvier’s rigid distinctions by claiming intermediate species, new homologies, and ascent; the defenders of Cuvier’s fixed classification scheme strove to locate any new specimens into existing rubrics and to deny intermediate or new status to them (something which might suggest links indicating transformations).
For example, in the early 1830’s newly detailed reports of the duck-billed platypus reached London and launched a heated argument about the classificatory status of this animal. Was it a mammal (as Owen insisted) or a new transitional type (and thus startling new evidence against Cuvier’s rigid distinctions in favour of serial development on the Lamarckian model)? The issue could only be determined by close anatomical attention to and skilled dissection of the animal’s ambiguous reproductive system (the combination of eggs and mammary glands was, for a time, a paradox) (23).
One fascinating source of evidence in many of these arguments was the famous museum collection of specimens and manuscripts left to the nation by England’s most eminent 18th century biologist, John Hunter (1728-1793), who had risen from a poor background to become surgeon extraordinary to the king and who had personally amassed a huge collection of over ten thousand anatomical preparations (24). The conditions of Hunter’s will were not adhered to, however, and in the 1820’s access to the collection was severely limited. Moreover, Hunter’s manuscripts had been extensively plagiarized by his brother-in-law and executor, Sir Everard Home (to compose over one hundred papers for the Royal Society’s Philosophical Transactions). Home had burned the original work or used the sheets for toilet paper. Largely through the efforts of Owen, Hunter’s son-in-law, who was hired to meet the radical effort to discredit the trustees of the museum, the museum was rebuilt in 1834 and the finest natural history collection in England made more accessible to all scientists.
The fierce arguments over the appropriate model for biological science quieted down considerably, however, in the late 1830’s and 1840’s, with something of a compromise. By this time the evidence for some type of evolution or progression (from fossils, embryos, homologies, and rudimentary organs) was becoming almost impossible to deny, and it was increasingly difficult to base one’s defense of non-progression on the argument from design (among other things, the existence of vestigial organs challenged the idea).
The followers of Cuvier and Owen therefore shifted their case away from design and, with the active help of S. T. Coleridge, developed a “higher” form of anatomy (25). This view conceded an evolutionary process, a “general ascent,” but one which expressed a divine will in Nature (the concept goes back to Plato’s archetypes or ideal forms) and insisted on withholding assent from any natural law governing the process.
This new synthesis, as developed by Owen (originally announced in a paper on fossils in 1841), saw changes as sudden (a “punctuated progression”), within different groups of animal life (i.e., evolution was not a single progressive staircase but involved separate groups). There had been no gradual transitions from one type into another, no transformations (as Lamarck had proposed), no environmental explanation of monstrosities or new species, no inner vitalistic striving by individuals. The changes of nature became the expression of God’s will and human beings the culmination of His effort.
The work Owen in this matter required all his considerable political and scientific skill. He succeeded in preempting the main argument in the radicals’ favour (progressive development) while at the same time holding onto enough of the old concept of Divine design to satisfy the establishment and to avoid the heresy of pantheism preached by Unitarians and Romantics. To Owen, more than to anyone else, must go the immediate credit for making evolution (at least among non-human animals) acceptable in orthodox British science (26).
For any proper understanding of the context of Darwin’s great book, it is important to remember that by 1859 the concept of evolution had been in the air for fifty years and had been hotly debated for over thirty years (at least). In principle, the concept had been largely accepted in the scientific establishment. At issue still were the mechanism by which it operated, the extent to which the Divine Will controlled the process, the basic shape of the lines of descent, and (most contentious of all) the status of human beings in the scheme. However, the radical political implications of evolutionary change had to a large extent diminished, and the establishment had for the most part reconciled itself to the idea, especially in scientific circles (27).
Moreover, an appreciation for the historical context of these arguments helps one to understand why Darwin was so reluctant to announce his ideas in the 1830’s and 1840’s and why he, in effect, delayed until the conflict had been largely resolved (even then he had to be pushed into publication) (28). In addition, one can appreciate just how lucky a man of Darwin’s temperament was to have the financial resources to carry out his work in comparative isolation from the fray. Unlike Grant, Darwin did not have to face the exhausting demands of heavy university work with little pay and preferment and ultimate poverty. Unlike Owen, Darwin did not have to dance attendance on lesser men who controlled patronage.
This is not to suggest, however, that Darwin’s reasons for delay were entirely determined by the social-political context and that he had to wait for reform sentiment to catch up with his challenging thesis. As a scientist raised in the English Baconian tradition, Darwin believed that a theory must be induced from observable facts. But evolution could not be observed directly, and the evidence for it (especially in the 1830’s) still contained large gaps (something critics of Darwin, echoing similar comments about Lamarck’s theory, were not slow to point out) (29).
In any case, the exhilarating pre-Darwinian chapter in the history of British biology established the setting for Darwin’s discovery, and we should not let his genius obscure the brilliance of those, like Cuvier, Grant, Owen, Lamarck, Geoffroy, Lyell, and many others, who, in a very real sense, made his achievement possible. It may be worth remembering that T. H. Huxley’s reaction to Darwin’s book was astonishment that no one had thought of the idea before, the issues having been so thoroughly discussed for years that they seemed obvious.
Finally, a knowledge of some of the arguments should remind us that in discussions of Darwin, we need to distinguish carefully the concept of evolution from Darwin’s particular account of it. This is an important caveat, because the argument for evolution does not rest upon an acceptance of Darwin’s theories (one does no particular harm to the general case for evolution by pointing out deficiencies in Darwin’s evidence, for example). In fact, the case for evolution is so strong that the concept is as scientifically true as any concept can be. However, there are still lively and continuing arguments about how evolution proceeds (especially about the rate, the direction, and the source of the changes).
Thomas Malthus (1766-1834)
To anyone considering the influences on Charles Darwin’s thought, the Essay on Population by the Reverend T. R. Malthus is, by Darwin’s own admission, particularly important. The book appeared anonymously in 1798. Malthus’s book is not about biology but about population. In it he laid down his well-known principle (which had been partially anticipated by Buffon) that since populations reproduce in geometric ratios (e.g., 2, 4, 16, 64, and so on) and food supplies increase only arithmetically (e.g., 2, 4, 6, 8, and so on) a stage must be quickly reached where the food is insufficient for the increasing population. Therefore, checks on population were necessary to reduce suffering.
Malthus’s main intended audience was not the scientific community, however. He was, in part, attacking proposed social reforms designed to alleviate the conditions of the poor. For Malthus
the great and radical defect of all systems of the kind . . . [is] that of tending to increase population without increasing the means for its support. . . .
Malthusian ideas were extremely influential in the 1830’s as the population problems came to a crisis. The Poor Law Amendment Act in 1834 adopted Malthus’s central idea by ending outdoor relief and forcing the genuinely sick poor into the intolerable workhouses (which broke up families and organized themselves like prisons). Radical response to what was called this “Malthusian Bill” was predictably violent.
What obviously attracted Darwin to Malthus, however, was not the political agenda (which probably went against his reform sentiments) but the image of constant struggle as the operative force in biological development.
. . . if we return to the principle of population and consider man as he really is, inert, sluggish, and averse from labour, unless compelled by necessity . . . we may pronounce with certainty that the world would not have been peopled, but for the superiority of the power of population to the means of subsistence. Strong and constantly operative as this stimulus is on man to urge him to the cultivation of the earth, if we still see that cultivation proceeds very slowly, we may fairly conclude that a less stimulus would have been insufficient.
The mathematical strength of Malthus’s argument provided Darwin with a central principle which his theory otherwise lacked: the competitive struggle for survival of all living things for limited resources.
Darwin’s Scientific Method
Darwin’s delay in publishing his theory involved factors other than the stormy political climate. For what he was proposing marked a significant departure from conventional English empirical science. At the heart of natural philosophy in England, as we have seen earlier, was an emphasis on observation and experiment. Even though most scientists did not follow precisely the Baonian emphasis on the primary role of empirical observation, nevertheless, they recognized the crucial importance of experimental testing of particular hypotheses.
This requirement presented Darwin with a grave methodological problem, simply because he was proposing a theory in which direct observation and experiment were clearly impossible, at least in the sense that a biologist could confirm the hypothesis of natural selection by observing it in the action of significantly transforming one species into another. Obviously, the time spans involved and the often minute succession of variations by which one species developed out of a species with quite a different appearance (e.g., reptiles from fish) meant that no direct testing by observation and experiment was possible.
To meet this difficulty, Darwin developed a new scientific procedure, now known as the hypothetico-deductive method. He first developed a theory, relying upon analogy and deduction to organize a plausible explanation, without direct empirical evidence, and then applied that theory to a wide range of facts, to demonstrate the explanatory power of what he was proposing.
More specifically, Darwin sought to meet the lack of direct observational evidence for natural selection in action by, first, arguing from an analogy with the practices of domestic breeding (especially of pigeon fanciers and livestock breeders). Because we can observe the production of new varieties in domestic breeding, we can infer the operation of the same processes in nature itself.
Secondly, Darwin accepted the deductive argument from Malthus about the geometric increases in population leading inevitably to a struggle for existence, on the ground that the necessary food supplies could not increase at the same rate.
Combining his argument for varieties in nature with the mathematical logic of Malthus, Darwin constructed his theory of natural selection, which argued that in the struggle for existence those varieties with some advantage prospered more than other varieties and thus passed on their slightly different qualities to their offspring. Over the space of many, many generations, these small variations would accumulate to produce organisms significantly different from the original parents (i.e., a new species would develop).
The third part of Darwin’s case (which takes up most of the Origin of Species) concerns the application of this relatively simple theory to a wide range of natural phenomena. Darwin obviously believed that, if he could demonstrate the enormous explanatory power of this idea, then he might overcome some of the obvious empirical weaknesses in his starting points. As Darwin’s son observed,
I must freely confess, the difficulties and objections are terrific; but I cannot believe that a false theory would explain, as it seems to me it does explain, so many classes of facts.
This method of presenting his case accounts for the wide-ranging scope of Darwin’s book, for he is eager to persuade the reader that his idea of natural selection is a great unifying principle which can be applied equally to paleontology, geographical distribution, embryology, and other areas.
Darwin’s method, which has developed into an important principle of scientific inquiry, did not, however, quickly convince all his colleagues. For many of them, the method looked suspiciously unscientific. The weakness of the analogy from domestic breeding is at once apparent. It might be true that human efforts could produce new varieties (of pigeons, racehorses, and roses, for example), but Darwin’s theory was making a much bolder claim, namely, that such a process could produce a range of entirely new species. It’s one thing, critics pointed out, to show that nature (or human effort) can vary an original parental stock in some interesting ways. But it’s quite another to argue that the same process can turn a fish into a bird, a cow, or a kangaroo.
Similarly, although Darwin’s contemporaries agreed readily enough with Malthus’s analysis and his conclusions about the struggle for existence, they were unable to agree whole heartedly with all the claims Darwin made about what natural selection could achieve. Many believed that there must be something else at the heart of the evolutionary process, for surely small (and especially random) variations could not account for the enormous complexity and specific functionality of organs like the eye or the hand.
The application level of his theory ran into difficulties, too. The nature of the fossil record was a problem. Darwin himself recognized the deficiency (a significant lack of transitional types left behind in the rock layers) and expressed the hope that future research would resolve the difficulty. Even today, that has not happened (at least not in the way strict Darwinian theory demands).
Given Darwin’s total commitment to natural selection as operating on the individual level, the theory had difficulty dealing with altruistic behaviour (e.g., cooperative behaviour between members of the same species). Similarly, Darwin’s ideas of sexual selection at the individual level could not satisfactorily cope with the continuing presence of sterile varieties in insect colonies.
More immediately serious for the reception of Darwin’s theory was a series of objections from the physicists about the age of the earth. On the basis of the work of William Thompson (Lord Kelvin) concerning the changing temperature of the earth, Fleeming Jenkin, a Scottish engineer, in a review of Darwin’s book, argued that the earth’s temperature could not have been suitable to sustain life for the length of time that Darwin’s theory demanded. Moreover, the best scientific estimates had established the age of the earth as about 98 million years, a direct challenge to Darwin’s calculation that the mammals had been in existence for at least 300 million years.
The result of such scientific objections (there were others, especially concerning Darwin’s notion of inheritance, which we will consider in Section Five) was that, in the years following the publication of Origin of Species, while the general doctrine of evolution in some form or another grew to general acceptance, Darwin’s particular version of it did not win over the entire scientific community. To achieve that success, Darwin’s theory had to wait until twentieth century geneticists could provide convincing details of and theories about the basic processes of molecular genetics and thus fill a central gap in Darwin’s theory, an adequate account of the production and heritability of variations. In addition, the discovery of radioactivity quite changed the earlier calculations about the earth’s age in relation to its loss of heat.
Evolution After Darwin
While it is beyond the scope of the narrative in this section to follow developments in evolutionary biology after 1859, a word of two on the continuing debate over the issues considered in this section may be in order.
Darwin’s achievement is frequently compared to Newton’s. Without assessing that comparison, one should note that, in one respect at least, their contributions had very different immediate effects. Whereas Newton’s physics quickly convinced most of his colleagues (especially in England) and within a century was the central theory of all physics, Darwin’s version of evolution had a much cooler reception. His work certainly encouraged the scientific community and the general public to accept evolution (within ten years of the publication of Origin of Species, Darwin could write of the “now almost universal belief” in evolution), but his explanation for the process had largely slipped from favour by the end of the century, mainly because of the scientific objections mentioned above.
The modern revival of Darwin, what has been called the “Modern Synthesis,” in this century (starting in the 1930’s) is commonly called neo-Darwinism. This is a synthesis of Darwin’s theory of natural selection and uniform rates of change with molecular genetics and population studies as the basis for variation and speciation. This has become the modern orthodoxy in study of biology.
However, many of the old disputes are still very much alive, especially in the general public. The best known (but the least intellectually interesting) is the Creationist-Evolutionist debate, a modern version of the arguments about the relative truths of scripture and natural philosophy (by one estimate about half the population of the United States does not accept any scientific account of evolution).
In addition, however, and more scientifically challenging, is the re-emergence of interest in catastrophism, the inheritance of acquired characteristics, guiding morphological principles of unity (laws of form), and other issues outside the framework of neo-Darwinism. These have arisen, in large part, because of certain problems which neo-Darwinism cannot seem to answer to everyone’s satisfaction. Consequently, many of those concerns so hotly debated in the 18th and 19th centuries are, in one way or another, still alive (30).
Notes to Section Three
(1) In a study of the work of the great astronomers, one does not have to deal with such a huge and always increasing number of different phenomena. For the most part, there was agreement about what a planet was, how many there were, and what constituted a fixed star. The real challenge was to measure the motion of the planets as accurately as possible and to establish a mathematically coherent model which could explain the structure of the entire system of planets. This is not to say, of course, that new phenomena never appeared (e.g., comets, a new planet) or that there were no arguments about how to classify all celestial observations or that developments in modern astronomy have not made astronomical classification much more complex. [Back to text]
(2) P. C. Ritterbusch, Overtures to Biology (New Haven: Yale UP, 1964), qu. in Crisis in Evolution, 13. The best known book on this metaphor, and a classic work in the history of ideas, is A. O. Lovejoy’s The Great Chain of Being (NY: Harper, 1960). For a more detailed discussion of the Great Chain of Being and a study of its transition into evolutionary theory see Eiseley, Chapter 1 “The Age of Discovery.” [Back to text]
(3) Not surprisingly perhaps, an artificial system can create unexpected difficulties. For example, in 1884, some English biologists seeking to trace the evolutionary stages of development from the gorilla used pelvic measurement as an indicator. This led to the unwelcome conclusion that white European women were the most advanced mammalian form. To reverse this conclusion, the researchers switched the criterion from the pelvis to cranial measurements, a move which restored European man to his rightful place at the pinnacle of created life. [Back to text]
(4) For an illustrated description of Ray’s animal classification system see Singer 185. [Back to text]
(5) For more detail on the work of Linnaeus see Eiseley, Chapter One. And Rook has some selections of Linnaeus’s writings. [Back to text]
(6) For a useful short study of Erasmus Darwin’s writings, see Roy Porter, “Erasmus Darwin: Doctor of Evolution?” in Moore 39-69. [Back to text]
(7) For a more extensive discussion of these two principles, see Crisis of Evolution, p. 10 ff., the basis for the brief discussion of these points here. [Back to text]
(8) Sometimes the two theories were not clearly separated. A very early and influential example (mentioned in Section One) is the work of William Harvey (1578-1657), who discovered the circulation of the blood and published his book on the subject in 1628. He might well be considered a mechanist, for his book is a milestone in the history of modern scientific physiology. But Harvey, unlike Descartes, stressed final causes and insisted that blood must contain a vital spirit. [Back to text]
(9) For a more detailed study of the fascinating scientific debates about this issue, see J. Farley, “The Spontaneous Generation Controversy (1700-1860),” Journal of the History of Biology 5.1 (1972). [Back to text]
(10) It was not always clear whether parents always had to be involved in reproduction. Antony van Leeuwenhoek (1632-1723), a Dutch draper, who spent all his spare time on microscopy and who is regarded as the originator of the science of histology, concluded that parthenogenic reproduction (i.e., without a male parent) took place among some aphids. [Back to text]
(11) In the view of L. Eiseley (in Darwin’s Century), “Buffon managed . . . to mention every significant ingredient which was to be incorporated into Darwin’s great synthesis of 1859.” For a critical analysis of this remark see Crisis of Evolution, 27 ff. [Back to text]
(12) Cuvier was not only one of the most famous scientists of his age; he was also one of the most powerful. As permanent secretary of the Academie des Sciences, professor of comparative anatomy at the Museum, chancellor of the university, a councillor of state, and one of the chief formulators of educational policy, his influence in France was enormous. Not surprisingly, his work, which strongly opposed directing attention into grand theories of progressive development in biology, set an inspirational standard for English conservatives striving to stem the tide of radical science (most notably from Cuvier’s colleague Lamarck). Sir Robert Peel, an English Prime Minister, had a portrait of Cuvier in his private gallery. [Back to text]
(13) The principle of correlation of parts holds that organs do not exist or function separately but as parts of a very complex interrelated organic system. Thus, an animal with feathers will have a certain kind of collar-bone (and vice versa) and other organs will fit accordingly. On the basis of this principle, then, it is possible to make very large inferences about the total structure of an animal of which one has only a relatively small piece of evidence. Cuvier was an outstanding pioneer in the reconstruction of fossil remains based on partial evidence. Similarly, William Buckland, on the evidence of petrified dinosaur dung, could infer the characteristics of its abdominal structure, and Robert Owen, the noted British anatomist, taking this principle to the limit, could reconstruct an entire dinosaur skeleton for public display (in 1841). The correlation of parts was (and still is) a vital principle in solving many problems posed by incomplete fossil remains. [Back to text]
(14) Cuvier’s taxonomy appeared in his best known work, Le Règne animal distribué d’après son organisation pour servir de base à l’histoire naturelle des animaux, et d’introduction à l’anatomie comparée (1817), the most comprehensive system for animal classification since the work of Linnaeus. Unlike Linnaeus, Cuvier had no interest in an Aristotelian scale of nature or a Great Chain of Being. The animal kingdom was divided up into four main groups, the main criteria for divisions being two sets of functions (and the organ groups essential to them): heart-circulation-respiration (the vegetative functions) and the brain-spinal-chord-muscle system (the animal functions). Cuvier, in other words, was striving to organize a natural rather than an artificial system of classification. [Back to text]
(15) For accounts of the most immediate “anticipations” of Darwin’s theory see Eiseley, Chapter V (“The Minor Evolutionists”) or, better perhaps, Darwin’s own account, “A Historical Sketch of the Progress of Opinion on the Origin of Species, previously to the Publication of this Work, a preface Darwin added to later editions of The Origin of Species. [Back to text]
(16) A discussion of Lyell’s treatment of Lamarck occurs in Crisis of Evolution 35 ff. [Back to text]
(17) One writer at least has stressed that one should not jump too quickly to see Lamarck’s evolutionary system as essentially similar in principle to Darwin’s. Lamarck believed in spontaneous generation and thus simple organisms could conceivably start an evolutionary path at any time. Darwin’s theory, however, stressed that evolution was an irreversible and non-repeatable process. Extinction was for ever (Crisis of Evolution 34). For a more detailed look at the origins of evolutionary thought see Futyma, Chapter One. In recent years there has been a resurgence of interest in the inheritance of acquired characteristics, a development which gives some resonance to Lamarck’s epitaph, inscribed on his tombstone: “Posterity will admire and avenge you.” [Back to text]
(18) In a letter to Wallace (the co-discoverer of natural selection) Darwin made his reasons clear: “You ask whether I shall discuss ‘man.’ I think I shall avoid the whole subject, as so surrounded with prejudice; though I fully admit that it is the highest and most interesting problem for the naturalist.” Darwin did not, however have to look beyond his own family for warning signs. His grandfather’s theories of evolution, relatively acceptable in the 1780’s, were in the first decades of the 19th century thoroughly abused, one more sign of the change in the intellectual climate. [Back to text]
(19) The influence of radical French science in Britain in the early 19th century was significant. While Oxford and Cambridge remained bastions of orthodox biology, Edinburgh attracted a number of radical lecturers educated in France by Lamarck and Geoffroy. The establishment of the University of London in 1827, the first secular university in England, fostered the radical cause, for a number of university appointments provided lectureships in London for Scottish radical anatomists, notably Robert Grant, who, while at Edinburgh, had first introduced the young student Charles Darwin to the ideas of Lamarck. The recruitment of French-educated Scottish academics was a deliberate move, which had the support of the dissenters, to overhaul the education of scientists, especially doctors, by introducing the sort of reforms which the French (the acknowledged leaders in biology) had carried out decades earlier. [Back to text]
(20) Homologies or homologous organs are similar structures in different species which appear to have remained in the same basic pattern despite millions of generations. For example, the limbs of man, dog, horse, whale, bird, and bat, for all the very different functions they serve, appear to be similar enough to be derived from some underlying ancestral form. The similarities invite some speculation about a law of derivation from a common ancestor. [Back to text]
(21) It is tempting in the light of such a remark to see Chambers as a precursor to Darwin. But by 1844, when Chambers’s book first appeared, Darwin had already outlined his own theory. And Chambers was not addressing, as Darwin was, the problem of speciation. Chambers was, by contrast, seeking a popular demonstration of the universality of God’s laws, an endorsement of the argument from design. This concept of evolutionary development of the embryo received its most famous definition in the expression of the German professor of Zoology at Jena, Ernst Haeckel (1834-1919): “Ontogeny recapitulates phylogeny.” In Haeckel’s words: “The individual repeats during the rapid and short course of its development the most important of the form-changes which its ancestors traversed during the long and slow course of their palaeontological evolution.” Haeckel is a very important and interesting scientist in his own right, famous as the great popularizer of Darwin’s theories in Germany (he earned the nickname Darwin’s dachshund). For study of Haeckel’s work and its political context in 19th century Germany see Paul Weindling, “Ernst Haeckel, Darwinismus and the Secularization of Nature” in Moore 311-327. For a less flattering view of Haeckel (with attention to his manipulation and falsification of evidence) see Hitching 173 ff. [Back to text]
(22) The quoted defense of the ladies was undertaken in a very hostile review of Chambers by Adam Sedgwick, the well-known geologist and strong defender of orthodox religious and social values. [Back to text]
(23) In this case, Owen had by 1834 won the debate. His role as the spokesman for the establishment gave him a certain advantage, for the Royal Navy saw to it that he had an adequate number of specimens to dissect. Geoffroy, by contrast, was constantly writing to London for details. As a public reward for this triumph (which involved a great deal of chauvinist talk of defeating “la grande nation”), Owen was elected a fellow of the Royal Society. A similar argument arose over the fossil remains of the Stonesfield “Opossum.” See Desmond for a detailed account of the scientific work and the political in-fighting around these issues. [Back to text]
(24) Hunter’s dedication to science was (and is) legendary. The story goes that to explore the nature of venereal disease and to test cures, Hunter deliberately infected himself with syphilis, a disease which killed him. The couch on which he lay raving as he was dying is still on display in a London hospital. [Back to text]
(25) Coleridge had, by this time, long abandoned his earlier radicalism and become the most famous and respected philosophical spokesman in England for the hearth-and-home counter-reaction to any reform on the French model. As the so-called “Sage of Highgate” he attracted many disciples. In his work his often unacknowledged appropriation of German ideas not yet disseminated in England was important (early in the 19th century few British intellectuals were familiar with German). Coleridge’s hostility to the political implications of French science is indicated by, among other things, his letter to the prime minister Lord Liverpool (in 1817) that the religious, political, and social upheavals in England were the direct results of the diseased “speculative science” produced by the French Revolution. [Back to text]
(26) Owen, as one might expect, did not like The Origin of Species, and responded to it with a long, bitter, and scientifically questionable criticism. Darwin, with his customary social tact, politely acknowledged Owen’s objections but did not engage him in direct debate. [Back to text]
(27) One should remember, too, the public nature of the arguments. Unlike earlier scientific controversies, which had taken place before the development of a popular press, the 19th century arguments about species were conducted in public, in the journals, medical magazines, Punch, newspaper, and public exhibitions in the museums. [Back to text]
(28) The main outlines of Darwin’s argument were ready by 1839. He sketched out a summary in 1842, which he later expanded into a 250 pages essay in 1844. He was finally precipitated into announcing his theory when he received from Wallace a document which outlined the same idea. The first presentation of Darwin’s theory was on July 1, 1858, about two weeks after Darwin received Wallace’s paper (Wallace was in the Far East). At a meeting of the Linnaean Society, in front of twenty-five scholars, papers by Darwin and Wallace were read, along with five others. The event caused no stir. Both papers were published in the Journal of the Linnaean Society for that year, and the president of the society in his annual report noted that the past twelve months had not been noted for any remarkably new developments in scientific discovery. [Back to text]
(29) Darwin himself, with his usual frankness (or rhetorical skill), acknowledged the problem: “The number of intermediate varieties, which have formerly existed on the earth, must be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory.” For all Darwin’s hope for useful later discoveries, this serious problem has not gone away, at least not in some people’s view. According to N. Heribert-Nilsson, of Lund University, “the fossil material is now so complete that the lack of transitional types cannot be explained by the scarcity of the material. The deficiencies are real, they will never be filled.” Nilsson’s claim has, however, been strongly challenged by modern scientists who point to the rapidly growing evidence of hitherto unknown transitional types and our enhanced ability to construct evolutionary genealogies based on this evidence. [Back to text]
(30) One of the most readable accounts of the modern questioning of neo-Darwinism is Hitching, who provides a rapid although rather cursory review of those recent developments in biology which are directing attention away from the new synthesis into issues which call into question the adequacy of the modern version of Darwin’s theory. Three of the most pertinent issues are the following: (a) fossils appear to indicate a series of evolutionary leaps rather than gradual progressive change; (b) genes appear to be stabilizing mechanisms designed to keep new species from evolving; and (c) the connection between random step-by-step mutations at the molecular level and the organized and growing complexity of life seems problematic. See Hitching 83, and, for an energetic defense of Darwin, Dawkins.
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