Evolution Theory
Before Darwin
Beyond Darwin
Synthesis I
Synthesis 2
Hominid Evolution
Origin of Culture
Brief Biblio
Expectations and Concerns of At-home DNA Tests
The Best DNA Tests for You
Discussion Board
Section I: Chapter 4

A History of Evolutionary Theory Part 3: Darwin and Beyond

Alfred Russel Wallace

Early in 1858, while hunting for specimens in the jungle of Moluccas, forced to rest from the rigors of malaria (Boorstin, 1983), Wallace (1823-1913) experienced an "ah ha." Suddenly it seemed evident to him that the principles of Malthus could be applied to the transformation of one species into another thus explaining the evolution of life on earth. Wallace knew another man who had travelled around the globe and might be able to relate to his newly discovered theory. Darwin received Wallace's missive later in 1858, the time when Darwin first learned he was not alone in his alternative view of nature. It was agreed that Darwin and Wallace would publish papers together and they did so before the end of the year.

Wallace was a younger man than Darwin, more open minded in some ways and seemingly less so in others. The two men did not agree on many things, though they maintained a life-long respect for one another. Wallace had a culturally relativistic perspective anomalous for his time. Wallace did not have that reflexive sense of Victorian England's superiority, and so certain cultural implications of natural selection seemed less opaque.

Wallace did not view the "savages" of his time as being a qualitative rung lower than Europeans in the hierarchy of intelligence and an ability to appreciate beauty. He was fascinated by his observation that demands of aboriginal life seemed to hold no survival contests that could explain the ability of humans to 'excel' to the degree that humans obviously had in Europe; that though they had the same potential in native cultures, they had not done so. (Eiseley, 1958). Wallace (Eiseley 1958) focussed on the brain as the source for culture and all that culture had accomplished, and concluded that the brain's ability to transcend nature, made it possible to actually drive human evolution outside the sphere of natural selection by making it unnecessary for humans to specialize in ways that all other species were forced to by their environment. Focussing on the brain, language, and beauty of song (1895), and the relative hairlessness of humans, Wallace (1895) concluded that natural selection did not drive human evolution, God did.

Deeply disturbing to Darwin was Wallace's relying upon teleological arguments, purposeful acts of god, to explain natural phenomena. Ironically, Wallace in some ways was more a materialist than Darwin. On numerous occasions Wallace reproved his older colleague (Eisely, 1958) for qualifying his writings with passages that stated that natural selection was not wholly responsible for evolution.

"Darwin, it is true, says -- 'There can be little doubt that the tendency to vary in the same manner has often been so strong that all the individuals of the same species have been similarly modified without the aid of any form of selection.' {Origin of Species, p. 72} But no proof whatever is offered of this statement, and it is so entirely opposed to all we know of the facts of variation as given by Darwin himself, that the important word "all" is probably an oversight." (Wallace AR (1890) Darwinism. MacMillan: London p. 141)

Particularly aggrievious to Wallace was Darwin's leanings toward Lamarckian explanations for the generation of variation, a seeming contradiction to the principle that natural selection was founded on random variation.

Wallace wrote at length supporting his belief that sexual selection did not occur. He ascribed some of its evidence to the mimicking of one species by another for various naturally selected benefits, or the advantage of bright colors for the male sex (usually) of a species to lure predators away from the nest of the less brightly colored mate. The struggles that Darwin and Wallace faced 130 years ago, to explain the evidence of sexual selection while at the same time seeking to understand how humans evolved, are at the center of the work of a number of contemporary theorists and will be explored as a continuation of the work that these two men began.

An issue that plagued natural selection theorists, which was not resolved until the convergence of the theories of Mendel and Weismann, was the belief by many that any trait, once established in an individual, would be "swamped" out of existence by the creation of progeny over a period of generations with only a fraction of a chance of exhibiting that characteristic. Wallace (1890) noted that there was a tendency for animals to clump together, like with like, even within species, which could lead toward the reinforcement of specific tendencies in evolution. Darwin (1868) had noted this in domesticated species. This is an example of one of many areas in which the two men saw the world very similarly.

George Mivart

On the Genesis of Species by George Mivart (1827-1900) was published in 1871. Its title suggests his primary point: Mivart states (1971) that Darwin's theory of natural selection emphasises how species achieve stability while he hypothesizes that the origin or genesis of species has little to do with natural selection but everything to do with variation in progeny engendered by the acquisition of characteristics from parents exposed to varying environments compelling use or disuse of specific organs. Mivart was a Lamarckian. In other words, by applying Mivart's theories, Darwin's natural selection operates on what was 'born fit' (Gottlieb, 1992), as opposed to a 'survival of the fittest' which is the interpretation of the theorists supporting natural selection.

Gottlieb (1992) describes an important nuance of Mivart's position and this is that evolution can unfold according to environmental pressures on embryos which directly influence the features of individuals. Mivart was the first theorist to emphasize the influence of the environment directly on early growth, though the idea had originally been brought forth by Bonnet. Individual ontogeny, influenced by the environment, resulted in changed growth trajectories which evidenced themselves in revised behavioral and physiological features. Mivart emphasized that these features were inheritable by their progeny.

Von Baer's work had been examined by Darwin and used to support his position that evolution had occurred. Mivart's use of this same material suggested that evolution may have occurred specifically by changes in ontogeny, in early growth, that compelled evolution to diverge in just the ways that von Baer had been describing.

Edward Drinker Cope

Cope's, Origin of the Fittest was published in 1887 followed in 1896 by Organic Evolution. Cope, along with Alpheus Hyatt, led the American Neo-Lamarckian movement of evolutionary theory. Soaking up nuances of theory from a vast variety of sources, Cope gave birth to several new concepts that have powerful relevance to the synthesis that this work represents.

Cope (Gould, 1977), like Mivart, placed a heavy emphasis on the origin of variation. He criticised Darwin for paying relatively little attention to the processes behind the generation of variation. Cope described in detail the manifestation of those processes through what he called the acceleration and retardation of evolutionary development.

"If the parents were like the individuals of the more completely grown, then the offspring which did not attain that completeness may be said to have been retarded in their development. If, on the other hand, the parents were like those less fully grown, then the offspring which have added something have been accelerated in their development." (Cope, CD (1887) The Origin of the Fittest. Arno Press: New York p. 10 )

Cope (1887)believed that natural selection performed the vital job of preserving species once they had been created, but that the generation of genera was caused by the environment compelling the use and disuse of organs. Cope's (1887) view of species was informed by his focus on the changing states of development. The most profound change, differences between genera, occurred through variation caused by the environment. He believed the species change could be caused by natural selection.

Haeckel (1834-1919) and Cope carried several concepts in common, yet differed in some important areas. Cope (1887) developed several important theories the basis for which were, in Haeckel's terms, idiosyncratic exceptions. One theory, what we now call mosaic evolution, Cope (1887) conceived of as a common evolutionary deviation whereby an individual organ or part of a body diverges during species evolution so that instead of an "exact" parallel development of all body parts you get an "inexact" metamorphosis with different parts of a single individual diverging as those parts respond to different pressures.

The Environment

Although a supporter of natural selection as a preserver of species, as a Lamarckian (Blatcher, 1982) Cope believed in the use and disuse of organs caused by the influence of the environment. Cope wrote (Gould, 1977) that adolescent individuals were most vulnerable to the results of use and disuse causing the acceleration or retardation of features inheritable by progeny. Species change according to transformation in one of these two directions propelled by the advantages of modified bodily functions responding to changing environmental conditions. Natural selection freezes those transformations stabilizing species change.

As an example of this process Cope (1896) described transformations experienced by a species of brine shrimp from 1871 to 1874. Their natural environment was dramatically changed by a radical variation in temperature and salinity, which resulted in species transformation, eventually generating a new genus. Researchers were able to reverse the process by removing the shrimp and running the sequence backwards. Cope (1896) also noted that diet apparently could radically effect the appearance of species under domestication, an issue Darwin had earlier addressed.

Diverging from Mivert's conclusions that the environment can profoundly influence an individual early in ontogeny thereby resulting in evolutionary change, Cope (1896) believed the adolescent and adults of a species were most easily impacted by the environment. These individuals manifested the impact in the form of acceleration or retardation.

Acceleration and Retardation

"The results as bearing on the doctrine of evolution were published in 1869 (in "The Origin of Genera"). It was there pointed out that the most nearly related forms of animals do present a relation of repression and advance, or of permanent embryonic and adult type, leaving no doubt that the one is descended from the other. This relation was termed exact parallelism. It was also shown that, if the embryonic form were the parent, the advanced descendant was produced by an increased rate of growth, which phenomenon was called acceleration; but that if the embryonic type were the offspring, then its failure to attain to the condition of the parent is due to the supervention of a slower rate of growth; to this phenomenon the term retardation was applied. It was then shown that the inexact parallelism was the result of unequal acceleration or retardation; that is, acceleration affecting one organ or part more than another, thus disturbing the combination of characters which is necessary for the state of exact parallelism between the perfect stage of one animal and the transitional state of another. Moreover, acceleration implies constant addition to the parts of an animal, while retardation implies continual subtraction form its characters, or atrophy. He had also shown ("Method of Creation," 1871) that the additions either appeared as exact repetitions of pre-existent parts, or as modified repetitions, the former resulting in simple, the latter in more complex organisms." (Cope, CD (1887) The Origin of the Fittest. Arno Press: New York p. 125)

Cope believed that a combination of both an increase in the number of stages in a succession of species (acceleration) and a decrease in the number of those stages (retardation) furnished a balance that provided the engine behind evolution.

"I believe that this is the simplest mode of stating and explaining the law of variation: that some forms acquire something which their parents did not possess; and that those which acquire something additional have to pass through more numerous stages than their ancestors; and those which lose something pass through fewer stages than their ancestors; and these processes are expresses by the terms 'acceleration' and 'retardation'." (Cope, CD (1887) The Origin of the Fittest. Arno Press: New York p. 297)

Cope (1887) offers several examples of the process. Salamanders are commonly referred to and snakes are pictured in his work to show clearly how the sequences of transformation manifest themselves in Cope's scheme. Cope believed that cases of acceleration outnumbered examples of retardation.

Hyatt and Cope parted in their view of evolution in very few areas and considered themselves the joint custodians of several concepts. Hyatt did not agree with Cope's belief that retardation was the complement to acceleration. In Hyatt's view (Gould, 1977), all species transformations could be explained by acceleration, with the apparent withdrawal or reversion into former stages being explained by a natural re-emergence of early ontogenetic stages very late in an accelerated process, an exhibition that might be compared to senility in human development.

Genetic Memory

Referring to the 1863 work of Sedgewick, Cope (1896) discusses the importance of memory, located in the germ (reproductive) cells, that is responsible for the ability of species to metamorphosize forwards and backwards in ontogenetic time following the trail of their forebears. Rejecting Darwin's particles, or gemmules, Cope proposed an 'energy' (Gould, 1977) capable of transferring the adaptive lessons engaged in by an organ (during use or disuse) so that the germ can log in, store, and pass on the revisions. Cope (1896) discusses how Weismann in 1893 agrees that there is evidently some process able to pass information through to the germ. Cope's proposed process was a Lamarckian concept contrary to the Weismann/Mendel synthesis and the Watson and Crick central dogma that would coalesce in the not too distant future. Butler (a notorious critic of natural selection) in 1878 (Blacher, 1982) also subscribed to the concept of heredity or inheritance tied directly to a memory store in the germ.

Developmental Delay and Humans

Cope's conceptual tools provided him with the opportunity to be the first (after St-Hiliare) to reveal a feature unique to humans, relative to their closest living relatives, what he described as developmental retardation, know today as neoteny or the maturational prolongation of infant features into adulthood.

"It must be noted here that the difference between the young and embryonic monkeys and the adults is quite the same as those just mentioned as distinguishing the young from the adult of man (Fig 1-2). The change, however, in the case of the monkeys is greater than in the case of man. That is, in the monkeys the jaws and superciliary ridges become still more prominent than in man. As these characters result from a fuller course of growth from the infant, it is evident that in these respects the apes are more fully developed than man. Man stops short in the development of the face, and is in so far more embryonic. The prominent forehead and reduced jaws of man are characters of "retardation." " (Cope, CD (1887) The Origin of the Fittest. Arno Press: New York p. 287)

Neoteny, a term coined by Kollman in 1885, was applied to humans by Cope (Gould, 1977). Cope (1887) believed this explained the difference between the different human races (Cope, 1887) assigning chimpanzee features such as jaw and calf structures to Cope's most un-European contemporaries. Focussing on the African physiology as an example of European/American superiority, Cope (1887) used his theory of acceleration and retardation to support his cultural biases. As in Darwin's case, where Darwin withdrew from an examination of female sexual selection when applied to humans because it may have resulted in conclusions contrary to the established social norms, Cope's insights pertaining to the possible influence of acceleration and retardation on varying populations of human beings was inhibited by social conventions that demanded the association of European white features with what was considered most advanced in evolutionary progress.

Ernst Haeckel

Ernst Haeckel (1834-1919) was not the first recapitulationist but he was its strongest proponent. Kielmeyer, in 1793, introduced the concept in a cogent form. Haeckel (Gould, 1977) popularized Darwin's evolutionary theories in Germany in work that was translated into over 20 languages. He was a proponent of both Lamarck and natural selection. He deeply respected von Baer who agreed with little that Haeckel had to say. He was a popular writer and a scathing critic of those who disagreed with him.

"Haeckel, in a statement of 1877, contended that "the cell consists of matter called protoplasm, composed chiefly of carbon, with a mixture of hydrogen, nitrogen and sulphur. These component parts, properly united, produce the soul and body of the animated world, and suitably nursed become man. With this single argument the mystery of the universe is explained, the Deity is annulled, and a new era of infinite knowledge ushered in." (Eiseley, L (1958) Darwin’s Century. Anchor Books: New York p. 346)

Haeckel could be described as an eloquent materialist (Gould, 1977) with a very powerful focus. He was firmly grounded in both Lamarck and Darwin's natural selection (Gould, 1977). Like Mivart, Cope and Hyatt, Haeckel believed that the environment via the use and disuse of organs, targeted variation to exhibit specific features that natural selection stabilized by culling out those individuals that couldn't make it to procreation age. His primary message emphasized that individuals are malleable enough to be changed only at the adult stage and that evolution progresses by the adding on of these revisions at the end of ontogeny (Gottlieb, 1992). Cope emphasized adolescent & adult vulnerability to environmental influences, Mivart believed that embryonic stages were easily influenced. Haeckel, by emphasizing the final or adult stage, and insisting that ontogeny or growth directly reflects this addition of features only at the final stage, compels the perception that ontogeny is an unfolding of miniature adults -- that ontogeny recapitulates phylogeny.

Condensation is the name Haeckel gave to the process whereby ontogeny unfolds by repeating the adult stage, the adult phylogeny of all ancestor species (Gould, 1977). Condensation is the squishing, accordion-like, of all ancestral stages into compact brief representations making possible an individual's growth in a reasonable period of time. Haeckel's theory was contrary to von Baer's original conjectures and removed from the process the zygote and embryonic stages of growth as possible sources for environmental influences. Haeckel's popularity and verve shifted focus away from alternative sources of evidence for the origin of variation. Thus, it was to be some time before there could be a focus on ontogeny itself (Gottlieb, 1992).

Haeckel, while concentrating on his overarching theme of evolution -- recapitulation -- or ontogeny recapitulating phylogeny, created names for the processes that describe the exceptions to this rule. Gould in his Ontogeny and Phylogeny, outlines Haeckel's exceptions.

"By far the most important were embryonic and juvenile adaptations. His favorite examples included the adaptations of free-swimming larvae to their own environments, and the superficial differences in cleavage and gastrulation that arise from variations in yolk content and obscure the unity of early development. But Haeckel also established a second category of cenogenesis: temporal and spatial dislocations in the order to inherited events. These include: (1) "heterochrony" - displacement in time, or dislocation of the phylogenetic order of succession (in the ontogeny of vertebrates, for example, the notochord, brain, eyes, and heart arise earlier than their appearance in phylogeny would warrant); (2) "heterotopy" - displacement in place." (Ontogeny and Phylogeny, p.82)

Haeckel coined the word, heterochrony, that we now use to describe changes in rates and timing of ontogological growth.

Beginning with the work of Wilhelm His (Gould , 1977) and the experimental biologists of the 20th century, (Gould, 1977), baby and bathwater went flying out the window. Swan (1990) makes the point that a concordance as opposed to a recapitulation between ontogeny and phylogeny has much to offer. Haeckel's unwillingness to accommodate alternative interpretations led to the eschewing of his theories.

"However, this discrepancy became understandable when it was realized that the newborn infant concords very well with 20 million years ago in the Miocene epoch, when our ancestors were apes of some sort. Newborn infants can often grasp and suspend themselves and even swing enough to suggest brachiation. Their hallux or big toe is often highly movable and the rest of their feet (showing a slope of their curled toes that is virtually transverse) are apelike. In an evolutionary sense, a newborn concords well with some ancestral Miocene ape. However, after nine months of a year, when the curve is found at the time of birth, a child approaches the evolutionary present. It starts to stand erect and practices with its lumbar curve before it walks upright. Its hallux assumes a forward position, and its starts to acquire the normal slope of human toes. The chin acquires a better-defined protuberance that expresses Homo sapiens as a species, and the jabberings of an infant transform into human speech." (Swan, Lawrence W. (1990) The concordance of ontogeny with phylogeny. Bioscience 40: 383)

Haeckel noted (Bowler, 1984) the nature of these relationships. He suggested that human brain size increases might be related to the freeing up of the hands when an upright stature was attained. Yet, as a sort of P. T. Barnum of evolutionary theory, Haeckel may, in the end, have educated less that he entertained. While he kept the focus on recapitulation, the potential magic of alternative theories of evolution disappeared.

August Weismann and Gregor Johann Mendel

August Weismann (1834-1914) assisted Haeckel in the "disappearing act" that culminated in the natural selection synthesis of the 30's and 40's. Blatcher (1992) quotes Weismann...

"In the first place it may be argued that external influences may not only act on the mature individual, or during its development, but that they may also act at a still earlier period upon the germ-cell from which it arises. It may be imagined that such influences of different kinds might produce corresponding minute alterations in the molecular structure of the germ-plasm, and as the latter is, according to our supposition, transmitted from one generation to another, it follows that such changes would be hereditary."

Weismann, of all people, was a Lamarckian (Matsuda, 1987). Cope (1896) and other Weismann contemporaries struggled with both Weismann positions 1) that the inheritance of acquired characteristics occurred in certain situations as in one celled animals 2) that the germ or sex cells (Eldridge, 1999) had walls that were inviolate, impenetrable by the 'gemmules' or 'energy' that could carry information detailing the changes that the physiology of the organism had made in response to the environment (Eiseley, 1958).

Unknown to Weismann when he created his germ theory, Gregor Mendel (1822-1884), a monk who was experimenting with pea varieties looking for patterns in inheritance, had made a profound discovery. Between 1856 and 1865 Mendel conducted experiments tracking the changing frequencies of features in garden peas when cross bred over a number of generations. Mendel concluded that hereditary factors (genes) determined the likelihood of inheritance of specific features based upon their being dominant or recessive. The paper he published in 1866 was not noted until 1900. Though it took a few years for the complementary aspects of the theories of the two researchers to sink in, the Weismann/Mendel synthesis formed the foundation for the wider acceptance of natural selection as the sole selective process. Gottlieb (1992) notes that the subtleties of epigenetic change were glossed over by the Weismann/Mendel synthesis. Specifically, the Weismann/Mendel synthesis has difficulty explaining the unfolding of phenotypes created by an interaction of several genes. But the elegance of the Weismann/Mendel model still holds sway. In the words of Gavin de Beer, this is the issue.....

"To put the matter as succinctly as possible, no case has yet been satisfactorily proved in which, as a result of external factors, the development of an animal has undergone a modification and in which these external factors have become internal and transmitted, so that the same modification has come to be invariably produced in all the subsequent ontogenies of descendant animals without the necessity for the external factors which originally evoked the modification. Until such a case has been proved, it cannot be believed that the effects of external factors and of use and disuse on body or mind are transmitted or play any part in ontogeny in subsequent generations. Somatic induction, or the transmission of the effects of use and disuse, constitute the kernel of the Lamarckian point of view; and it is curious that while we still lack evidence, viz. direct induction, though of course he was prophetic and correct in rejecting the view that direct induction can produce an adaptive inherited response to the environmental stimulus. It would be very convenient if it were possible to accept an explanation of the origin of internal factors and of their adaptive nature on the lines of Lamarck's hypothesis of the effects of use and disuse, but in the present state of knowledge it is not possible. It is necessary to adopt a humbler position and admit that the causes of origin and change in the genetical factors of organisms are unknown. Once they have arisen or changed (mutated), selection plays an all-important part in moulding their effects." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 15-6)

Baldwin, Goldschmidt, Garstang & Wright

At this point in our narrative the four strands, levels or themes introduced at the beginning of this work have reappeared in the writings of theorists from Bonnet to Weismann. The power of the environment to shape evolution is heralded by Boffon to be given full voice by Lamarck and Darwin. Darwin is shown to be the master composer of the selective process introducing natural selection and sexual selection eloquently and in great detail. He even attempts to give voice to a Lamarckian like dynamic that sounds like a distant echo of the influence of the sexual hormones on zygote creation. Mivart suggests that an embryo can be influenced in ways that will be transposable to the germ and inheritable by the next generation. No one has yet described how specifically the sexual hormones may act as the intermediary between somatic change and the passing on of those changes to the next generation, but that will soon come. Cope has detailed the power of developmental rates to effect evolution; Haeckel has identified this same possibility. So as we cross into the 20th century almost all four themes are being practiced, though no one has found a way to make music from them all. Clearly, Darwin has come closest. Once again, environmental influences, selective processes, hormonal intermediaries, and heterochronic change are concepts 100 years old and older, except that they have not been united in an attempt to generate a model describing biological evolution, human evolution, cultural evolution and the etiology of disease.

In 1902 James Mark Baldwin (1861-1934) published Development and Evolution. In this work he called attention to the possibility that natural selection chooses those individuals excelling in an ability to generate more rather than less variability (Gottlieb, 1992). He suggested that this innate ability to vary can be passed on to the next generation.

There is a rather profound, two levelled implication here. First, random selection has reason to select for highly adaptive individuals; not unlike what Wallace was suggesting when he said that the human brain had an ability to transcend selective pressures, except that Wallace brought in the deity to explain the anomalous nature of this characteristic. Second, the specific strategies these highly adaptive individuals use to generate their adaptive behaviors need to be examined. Natural selection may select or spawn other selective processes. Evolutionary rules may evolve.

Stephen J. Gould notes a new approach that theorists started to take at the beginning of the 20th century. Examining the evidence of genes in light of changes in development during ontogeny, conclusions have been formed that suggest that enzyme and hormone rate and timing changes may be influencing the evolution of individuals and species.

"As early as 1918, Richard Goldschmidt had spoken of "rate genes" (see Goldschmidt, 1923, and 1938, pp. 51-78, including discussion of Sewall Wright's {1916} studies of coat color in rabbits). He discovered that "genetic races" of the gypsy moth, Lymantria dispar, differed only in genes controlling the depositional rates of pigment in caterpillars. In some races, a pattern of light markings persists until pupation; in others, this pattern is gradually covered by a dark cuticular pigment deposited at definite rates. Goldschmidt found that those rates differed among races and were intermediate in heterozygous hybrids of intermediate color. Ford and Huxley (1927) studied eye coloration in the amphipod Gammarus chevreuxi. Red and black are Mendelian alternatives. In this species, all colored eyes (some are uncolored) are red at first and change to black as melanin is deposited at definite rates during development. Ford and Huxley discovered a set of genes that produced a graded series of colors by altering both the rates and times of onset for deposition of melanin. Goldschmidt generalized this theme:

"The mutant gene produces its effects, the difference from the wild type, by changing the rates of partial processes of development. These might be rates of growth or differentiation, rates of production of stuffs necessary for differentiation, rates of reactions leading to definite physical or chemical situations at definite times of development, rates of those processes which are responsible for segregating the embryonic potencies at definite times.' (1938, pp. 51-52)

'If genes produce enzymes and enzymes control rates of processes, what possible justification can be offered for universal acceleration in phylogeny? Acceleration, to be sure, does occur, but there is no reason to consider it any more fundamental, or even any more common, than retardation. The retardation of somatic characters usually results in paedomorphosis, while acceleration yields recapitulation. If both acceleration and retardation are equally valid in theory, then these results are equally orthodox. Paedomorphosis can no longer be cast aside as an exception to universal recapitulation. This new condition of "equal orthodoxy" is emphasized in J.B.S. Haldane's article on "The Time of Action of Genes, and Its Bearing On Some Evolutionary Problems":

'There has been a common tendency in evolution for development to accelerate, ie., for certain characters to appear progressively earlier in the life cycle...This presumably means that the time of first action of certain genes has tended to be pushed back...Another common tendency has been a retardation of certain characters relative to the life-cycle, so that originally embryonic characters persist in the adult. This is known as neoteny.' (1932, 00. 15-16; see also Huxley, 1923, p. 616)

"In writing his "critical restatement" of the biogenetic law, Garstang (1922) did not "discover" paedomorphosis or any of the other well-known exceptions to recapitulation. Instead, he recognized that they could no longer be dismissed as exceptional, for they were now the expectations of a new theory, and they demanded equal status with all the phenomena of recapitulation. Paedomorphosis is no "degenerative exception" to universal acceleration. Genogenesis is not the "secondary falsification" of an essentially palingenetic development. The facts that had lurked so long in limbo of exception were elevated to orthodoxy by the discoveries of Mendelian genetics." (Gould, S.J. (1977) Ontogeny and Phylogeny. Cambridge: Belknap Press. p. 205-206)

In 1922 Garstang, in a sweeping perspective that synthesized the views of any number of his predecessors, wrote that at any stage of ontogeny there could be variation (Gould, 1977), variation that would influence the ontogeny of following generations. Garstang specifically suggests that both the zygote and uterine stages of ontogeny are open to influences changing growth trajectories (de Beer, 1951; Gottlieb, 1992). He makes the logical leap, transcending almost a century of theory obsession with Haeckel's phylogeny dictating ontogeny, to a von Baerian orientation that notes that ontogenical change compels phylogenetic transformation (Gottlieb, 1992). Varying influences on the zygote and embryo are now noted as variables effecting evolutionary change. Garstang focuses on gene mutation as the prime candidate for ontological revision at these early stages.

Sewall Wright, into the 1920's, published the results of his experiments with guinea pigs, uncovering, as did Garstang, evidence of heterochronic processes, specifically the possible source of the effects of revisions in development during ontogeny.

'If, instead of tracing forward from primary gene action ... we consider everything that may affect a particular process at a particular time in development, these fall naturally into four categories: (1) local gene action, (2) the chain of past events in the line of cells in question, (3) correlative influences from adjacent cells and from other parts of the body, and (4) external environmental differences. Since the second and third may be analyzed, step by step, on this fourfold basis, and local gene action must be evoked by products of previous events, the ultimate factors are the array of hereditary entities in the egg and sperm and the succession of external influences." (Wright. 1968, pp. 58-59). (Gottlieb, Gilbert (1992) Individual Development & Evolution. Oxford Univ. Press: New York pp.117)

Louis Bolk

Geoffrey St-Hilaire, Lamarck's colleague, was perhaps the first to notice the evidence that human beings are developmentally delayed compared to our primate cousins. Cope explored this in some detail, constrained by the western compulsion to place non-western cultures in a less evolved position than members of one's own race. Louis Bolk (1866-1930) was also inhibited by the biases of his time, yet, as made clear by the Stephen J. Gould, the Dutch anatomist Louis Bolk was able to delineate in detail many features of our species that evidence heterochronic processes, specifically a form of maturational prolongation called neoteny.

Most of Bolk's work appeared in the 1920's. He detailed several human features characteristic of neoteny, including hair and teeth development.

"One of the most interesting cases of this kind is that of the hair, for Bolk has shown that a progressive series in reduction can be made out in the monkeys, apes, and man: 1. the monkey is born with a complete covering of hair; 2. the gibbon is born with the head and back covered with hair, and the other regions are covered later; 3. the gorilla is born with the head covered with hair, and the other regions are partially covered later; 4. man is born with head covered with hair, and the other regions are scarcely covered at all later. It is noted that the lanugo, which forms a very fine covering to the unborn infant before being lost, is also present in unborn apes. Further, the lanugo is retarded in man, for he has not completely shed it by the time of birth. This series shows that the neoteny of man as regards hair is associated with a progressive retardation in the rate of its development. This retardation in the rate of development of the body, it will be remembered, is all that is required to produce the other human features mentioned above. It therefore becomes interesting to inquire whether the rate of human somatic development is really slow as compared with that of other mammals. That this actually is the case is proved by a table which was given in Chapter III (p. 22). Bolk has been able to give additional proof of this by a study of the development of teeth. In the apes the milk-teeth are cut directly after birth, the 1st molar is cut soon after the 2nd premolar, and the replacement of the milk-teeth then takes place, accompanied by the cutting of the 2nd and 3rd molars. In man, the cutting of the milk-teeth is only finished two years after birth, and this is followed by a pause until at five or six the 1st molar is cut. After this, the milk-teeth are replaced, and not until this is done does the 2nd molar appear. The 3rd molar may be cut after the 2nd, but its development is often so retarded that it is not cut at all. Indeed, retardation characterizes the development of the human dentiton as a whole." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 58-9)

Darwin focussed on human hair patterns as evidence of sexual selection. Wallace thought human hair loss an act of god. Cope identified it as an aspect of human retardation. Bolk contextualized human hair reduction relative to other primates as evidence of neoteny or the prolonging of infant features into adult states.

The list of human neotenous features below were derived from De Beer (1951), Gould (1977) and Montegu (1989) based on Bolk's works. The list is patterned after Gould (1977) and abbreviated.

1) Non-prognatistic flat facial features: jaws and lower face that don't jut out like an adult chimpanzee's.

2) Reduced hair: both in density and coarseness. (Montegu, 1989)

3) Lightening in pigmentation: hair, eyes, and skin.

4) Foramen magnum positioning: in humans, the location of where the spine meets the skull is forward of where the joining is in our ancestor species (Bjorklund, 1997)

5) Heavier brain.

6) Cranial sutures (gaps between skull plates) unjoined until later in childhood.

7) Big toe runs parallel to other toes instead of groping out to the side.

8) Vaginal opening rotated forward.

9) Smaller teeth erupting later in childhood.

10) Skull shape longer (Montegu, 1989)

11) Prolonged period of infantile dependency.

12) Prolonged growth period

13) Increased life span

14) Myelinization occurs later: the nerve fiber sheathing prolonged (Montegu, 1989).

15) Imagination and creativity (Montegu, 1989)

16) Endocrine system variations (Montegu, 1989)

As Gould (1977) makes clear, evidence of neoteny in humans does not mean that all human features are exclusively derived from this process. Clearly, the selective processes have had a profound effect upon cultural variation, many of those tangents driven by the sexual selection of specific different neotenous characteristics and altogether non-neotenous characteristics. Section IV of this work is devoted to the details of that process based on the dynamic of matrifocal vs patrifocal social structures.

In addition to focussing on neoteny as the primary process responsible for human evolution, Bolk suggested how this process might have occurred. Gould quotes Bolk:

"The gradual retardation of life's course of the ancestors of Man with all the consequent effects, both as regards his morphological features and his functional properties, must have had for its immediate cause a modification of the action of the endocrine system of the organism .... In controlling the intensity of the metabolism these hormones can inhibit or promote the growth. In Anthropogenesis an inhibitive action appears to have gradually increased in significance, the rate of development became slower, the progress of development more retarded" (1926a, pp. 471-472). Therefore, Bolk argues in his most striking phrase: 'If I wished to express the basic principle of my ideas in a somewhat strongly worded sentence, I would say that man, in his bodily development, is a primate fetus that has become sexually mature....(1926c, p. 8)' " (Gould, S.J. (1977) Ontogeny and Phylogeny. Cambridge: Belknap Press.pp. 361)

In neoteny, the human hormonal system is transformed along with all the other features listed above, and yet, Bolk considers, specific hormones may drive the process of neoteny. Bolk states that human neoteny is characterized by premature sexuality. This means that an adult, with infant like features, becomes a sexual being. The implication is that sexual hormones may be closely tied to the neotenous elements of human development. Bolk makes the first suggestion of the bottom two levels of the four layered symphony we are exploring; hormonal intermediaries and heterochronic processes. Something (sexual selection? natural selection? external influences affecting early development in the womb? external influences changing the zygote?) is driving sexual hormonal levels up or down causing changes in the rate and timing of heterochronic processes, in this case neoteny or the prolongation of infant features into adulthood.

Gavin de Beer

Gavin de Beer (1899-1972) working from a firm foundation of the inviolability of the germ, the sex cells being uninfluencable by the environment (de Beer, 1951), hypothesized in 1932 that heredity reveals the specifics of an individual's ontogeny to respond to varying degrees of environmental or external influences (de Beer, 1951). He suggests that in some species the lowering and raising of the temperature is genetically predetermined to influence some individual's development in specific ways. "Heredity does not account for the individual, but merely for the potentialities some of which are realized in the individual. In other words, the internal and transmitted factors are by themselves unable to 'produce' an animal at all. (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 12).

A primary concentration of de Beer's work is the immense influence of external factors on ontogeny. Paying close attention to all possible derivations of rate and timing changes as a result of external factors, de Beer outlined several ontogenetic paths available, some of these paths having been first suggested by Haeckel as exceptions to recapitulation. Eventually, de Beer concluded that just about any growth pathway hypothesized, occurs (de Beer, 1951).

"De Beer was one of the few writers, outside of the experimental embryologists, to realize the conceptual inadequacy of Haeckel's notion of the relation of heredity to ontogeny. Rather than the passive translation of phylogenetic causes into ontogenetic happenings, ontogeny in each generation is a consequence of the coaction of hereditary or genetic factors and many different local environing circumstances that determine the expression of the phenotype during the course of development. " (Gottlieb, Gilbert (1992) Individual Development & Evolution. Oxford Univ. Press: New York p. 95)

De Beer's point is that focussing on the acquiring of adapted characteristics, noting whether the environment eventually changes the genes by use or disuse or direct environmental influence, is irrelevant. Hereditarily, each individual is programmed to accommodate external messages using the information to determine ontological direction (de Beer, 1951). External and internal work in concert following the tracts of developmental retardation and acceleration (Gottlieb, 1992).

De Beer uses the insights that his theory provides to conclude that evolution can occur at breakneck speed if external and internal factors combine to generate extreme retardation to accommodate unusual environmental conditions. "It is to be expected, therefore, that in those cases where paedomorphosis has occurred, resulting in the production of markedly new types such as the chordates, much of this evolution will have been clanestine, and there will be a gap in the record of fossil ancestors of the new type. In other words, the theory of paedomorphosis not only explains the gaps in the fossil record, but also supplies the reason why such gaps must be expected." (de Beer, G. R. (1951) Embryos and Ancestors. Clarendon Press: Oxford. p. 100)

The heterochronic themes covered in this work, starting with St-Hilaire's identification of what later would be called neoteny, leads to an examination of the changing rates and timing of maturation and development, as brought together by de Beer. He did not examine the specifics of selective processes and how they might compel evolutionary change, choosing natural selection by default. Instead, de Beer outlined eight heterochronic processes that he thought covered all possibilities of development. He focussed on the relative speed of maturation and development (the rate) and changes in onset (the timing). Gould simplified and clarified de Beer's system in 1977.

Not usually clear in writings on this subject is the difference between maturation and development. The words are often used synonymously, as it might seem like they have been until this point in this text. Clearly, different hormones are involved in growth in size or allometric scaling than the hormones guiding growth in maturity and sexuality. The two are easily confused. We grow larger at the same time that we grow more mature. The distinction between the two is not often made. Studies by Brian T. Shea and the writings of Stephen J. Gould have helped tease out their differences in human evolution. So, in this text, references to maturational growth, maturational delay, maturational prolongation, or maturational acceleration, puberty and progenesis will be references to changes in maturation rates and timing, and the sexual hormones. Changes in development referencing changes in allometric scaling, though important in other species and in human beings in other contexts, are not the focus of this work. For example, ground breaking work by Brian T. Shea & R. C. Bailey (1996) in their studies of African Pygmies focus on developmental growth or allometric scaling. Pygmies, though smaller, are not more neotenous. They are miniature adults as opposed to children grown up small.

R.A. Fisher

In 1930 R. A. Fisher (1890-1962) published The Genetical Theory of Natural Selection. Charles Darwin introduced two selective theories, natural selection and sexual selection, and gave his spin on a third Lamarckian selective process that he called pangenesis. Both natural selection and selective processes implying the direct influence of the environment, Lamarckian effects, were discussed at length for years with constant theory additions and revisions, until relatively recently. (Discussions of Lamarckian concepts were eclipsed by the natural selection synthesis of the 30's and 40's and languished until Gould's Ontogeny and Phylogeny, published in 1977.) This work has been following developments in several areas as they pertain to our four level dynamic. The changes in natural selection theory have not been detailed in this work because those nuances don't influence what we perceive as the dynamic of human evolution and disease formation. Sexual selection, and its central position in human evolution, does demand our focus. It was not until Fisher introduced his concept of runaway sexual selection in 1930 that sexual selection was again explored as an influential selective process. It wasn't until the 1970's that sexual selection achieved some momentum as a factor in human evolution.

Cronin (1972) notes that Darwin wrote in 1871, "there is no definite limit to the amount of advantageous modification; so that as long as the proper variations arise the work of sexual selection will go on." Fisher (1930) took this one step further.

"Fisher argued that choosing an attractive mate can be adaptive for a female because she will have attractive sons. In a population in which there is a majority preference for anything whatsoever, a female would do best to follow the fashion, however arbitrary, however absurd, because the next generation of daughters will inherit their mothers' preference whilst her sons will inherit their fathers' attractive feature." (Cronin, Helena (1992) The Ant and the Peacock: Cambridge Univ. Press, Cambridge p. 201)

In other words, in the selective process of runaway sexual selection, when a female picks a males for a specific trait, say longer tail feathers, she passes on to her male progeny the longer feathers of her spouse, and to her female progeny the desire and the behavioral tools to satisfy her desire for a male with longer feathers. The trait get passed on through both sexes. Individuals in the species without the trait are less and less likely to mate with members of the species with the trait, as members with the trait seek each other out and further reinforce the trait in each generation.

"In species so situated that the reproductive success of one sex depends greatly upon winning the favour of the other, as appears evidently to be the case with many polygamous birds, sexual selection will itself act by increasing the intensity of the preference to which it is due, with the consequence that both the feature preferred and the intensity of preference will be augmented together with ever-increasing velocity, causing a great and rapid evolution of certain conspicuous characteristics, until the process can be arrested by the direct or indirect effects of Natural Selection." (Fisher, R. A. (1930) The Genetical Theory of Natural Selection. Oxford. Clarendon Press pp. 145)

Alexander (1989), a contemporary theorist, makes clear that only species able to transcend the most crushing blows of a struggle to survive to procreation age will be able to engage, long term, in this process. Individuals of a species engaged in a runaway sexual selection loop will not be easily adapting to other environmental variables. There are costs to this process. Male displays can draw predators. Increasing testosterone levels heighten male colors. If testosterone levels become too high males become more vulnerable to infection and disease. Idiosyncratic male add-ons, longer tail feathers for example, can be a hindrance in the pursuit of food. Cronin (1992) describes how a larger size in male birds, if chosen by females, may increase beak size to a girth that forces these males into alternative food gathering strategies.

For a sociobiological single gene explanation of the process of runaway sexual selection, click on the year at the end of this sentence (Cronin; 1992). For a groundbreaking extremely useful introduction and overview of sexual selection as a force in human evolution by evolutionary psychologist Geoffrey Miller (2000), visit his book, the Mating Mind.

This work will explore the evidence that supports the hypothesis that sexual selection was integral to human evolution. But we are proposing that there is profound adaptive utility in the specific way that sexual selection drove human evolution, as female sexual selection choose males exhibiting neotenous characteristics. Fisher made clear that adaptive utility was unnecessary to generate a runaway loop. Wesson (1991), Miller (1994), Crow (1995), and Brin (1995) agree that there is evidence of adaptive utility in a feedback loop involving female choice and a prolongation of infant features into adulthood. This work will explore that thesis in detail.

Ivan Ivanovich Schmalhausen & Conrad H. Waddington

In 1949, an English translation of Schmalhausen's (1884-1963), Factors of Evolution: The Theory of Stabilizing Selection, appeared in this country (Gottlieb, 1992). In this work he hypothesized a huge reservoir of potential variability lies dormant waiting for messages from the environment so that the individual can commit to adaptive change. Schmauhausen suggests that individuals are genetically predisposed to adapt to changing conditions by their genetics, a complement, he believed, to the Darwinian synthesis emphasizing natural selection.

Conrad H. Waddington (1905-1975) conducted experiments on fruit flies that he published in 1953. Waddington blasted fruit flies with heat shock in their embryonic stage. Some survivors exhibited fewer or no crossveins on their wings. Culling out the individuals with fewer or no crossveins, he subjected their progeny to the same procedure. After 14 generations the crossveins appeared with no heatshock. There seems to be some form of genetic assimilation of the environmental experience. The results of Waddington's experiments are generally approached as anomalies.

"The link between environment and heredity in the origin of adaptation is explained by Waddington (1957) as follows. A population of organisms experience a new environment and respond developmentally in a novel fashion, that is, a phenocopy appears. As the population is heterogenous in modifier alleles, individuals will respond to varying degrees. If the response is adaptive, there will be selection for the modifier alleles which increase the initial intensity of the response and then (or at the same time) regulate it so that the same degree of response will occur within a range of intensity of the environmental stimulus. In other words, the response is canalized. Later, genetic assimilation takes place: the response now occurs in the absence of the environmental stimulus." Mae-Wan Ho (1984) Environment and Heredity in Development and Evolution in Beyond Neo-Darwinism. Hoo M, Sauders PT (eds.) Academic Press: London p. 272)

It is not immediately evident how these and other experiments can be gathered together to make a more useful model than that supplied by the Darwinian synthesis. An important aspect of the problem is that the neo-Darwinian synthesis is elegant and simple. In the next two chapters we will approach the material offered to you so far and reconstruct it into a form where its utility will become self evident.

Proceed to Chapter 5

human evolution