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Evolution, the modern synthesis
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January 14, 2025
THE INFLUENTIAL ‘SUMMING UP’ OF ‘NEO-DARWINIAN’ EVOLUTIONARY THEORY
English evolutionary biologist Julian Huxley (1887-1975; Thomas Henry Huxley---‘Darwin’s bulldog’---was his grandfather) wrote in the Preface to this 1943 book, “Even among professional zoologists the modern conception of natural selection and its mode of operation is quite different from that of Darwin’s day, but much of the research on which the changed outlook is based is so recent that the new ideas have not spread far. The idea of evolutionary progress, on the other hand, has been undeservedly neglected. Thus it seemed to me valuable to attempt to give a broad account of the two concepts and their relation to each other.”
He explains in the first chapter, “already we are seeing the first-fruits in the re-animation of Darwinism. By ‘Darwinism’ I imply that blend of induction and deduction which Darwin was the first to apply to the study of evolution.” (Pg. 13) He continues, “a struggle for existence… for survival, must occur… in Darwin’s time… the subject of inheritance was still very obscure… the principles of genetics had not yet emerged… there must be a differential survival of different types of offspring in each generation… SOME variation is inherited: and that fraction will be available for transmission to later generations… The term ‘Natural Selection’ … [has] two rather different meanings. In a broad sense it covers all cases of differential survival; but from the evolutionary point of view it covers only the differential transmission of inheritable variations.” (Pg, 15-16)
He continues, “The raw material for evolution by natural selection falls into two categories---mutation and recombination. Mutation …. alters the nature of genes. Recombination… though it may produce quite new combinations… only juggles with existing genes.” (Pg. 21) He goes on, “Mendelism is a theory of heredity… [It] is now … an essential part of the theory of evolution. Mendelian analysis … together with selection, explains the progressive mechanism of evolution.” (Pg. 26) He summarizes, “Neither mutation nor selection alone is creative… in evolution; but the two in conjunction are creative.” (Pg. 28)
He notes, “the demonstration that small mutations occur and can serve as the raw material on which natural selection may act to effect gradual evolutionary change, does not mean that this is … the only type of evolutionary change possible… species may be formed abruptly, and other large variations are known to … serve, in some cases, as building-blocks of evolutionary change.” (Pg. 41)
He outlines, “From the standpoint of the mode of action of natural selection, species… fall into two contrasted categories… we have those in which natural selection … merely acts upon the species as given, in competition with its relatives…. In which character-modification is abrupt and initial. On the other hand, we have those forms in which character-modification is gradual… These include … forms in which the separation of groups occurs by geographical, physiological, or ecological isolation, but also those in which the initial separation is genetic but involves no visible differentiation… groups separated ecologically will be exposed to a considerable intensity of selection to adapt them fully to their different modes of life.” (Pg. 384)
He adds, “If Darwin were writing today he would call his great book ‘The Origins,’ not ‘The Origin,’ of Species.” (Pg. 387)
He states, “in general, the preponderance of degenerative (loss) mutation will result in degeneration of an organ when it becomes useless and selection is accordingly no longer acting on it… constitutional preadaptation acts … [by] restricting inhabitants of specialized habitats … to forms with some definite predisposition to the peculiar mode of life involved… a constitutional preadaptation towards cold-resistance has led to certain… plants being able to survive in higher latitudes… various marine Crustacea … are able to tolerate waters of low salinity much more readily at high than at low temperatures… [Richard] Goldschmidt… has suggested that preadaptation may play a rather different role by means of large mutations giving what he styles ‘hopeful monsters,’ which can then serve as the starting-point for quite new evolutionary trends… I do not propose to discuss these rather revolutionary views… I disagree with them in general… However, even if we dismiss Goldschmidt’s views as unproven or unnecessary, preadaptation of various kinds has clearly played a not inconsiderable role in evolution.” (Pg. 455-457)
He asks, “How has adaptation been brought about? Modern science must rule out special creation or divine guidance… [Henri] Bergson’s ‘elan vital’ can serve as a symbolic description of the thrust of life during its evolution, but not as a scientific explanation… Bergson was a writer of great vision but with little biological understanding, a good poet but a bad scientist… Modern biology … also repudiates Lamarckism [the ‘inheritance of ACQUIRED characteristics’].” (Pg. 457-459) Later, he adds, “when numerous adaptations are shown to be incapable of Lamarckian explanation… [to] postulate Lamarckism to account for … others … would be to sin against the economy of hypothesis… William of Occam’s razor.” (Pg. 464) He continues, “Most biologists also look askance at orthogenesis [i.e., that organisms have an innate tendency towards some goal]… This is too much akin to vitalism and mysticism for their liking; it removes evolution out of the field of analyzable phenomena; and it… goes contrary to Occam’s razor. (Pg. 465)
He continues, “There can be little doubt that the apparent orthogenesis which pushes groups ever further along their line of evolution until, as with size in some mesozoic reptiles and armor in others… they are balanced precariously upon the edge of extinction… is due, especially in it is later stages, to be … induced by intraspecific competition. This conclusion is of far-reaching importance. It disposes of the notion… that all man need to do to achieve further progressive evolution is to adopt the most thoroughgoing competition… But we now realize that the results of selection are by no means necessarily ‘good,’ from the point of view either of the species or of the progressive evolution of life. They may be neutral, they may be a dangerous balance of useful and harmful, or they may be definitely deleterious. Natural selection, in fact, though like the mills of God, in grinding slowly and grinding small, has few other attributes that a civilized religion would call Divine. It is efficient in its ways---at the price of extreme slowness and extreme cruelty. But it is blind and mechanical; and accordingly its products are just as likely to be aesthetically, morally, or intellectually repulsive as they are to be attractive. We need only think of … a brood of ichneumon-flies slowly eating out a caterpillar.” (Pg. 484-485)
He argues, “The only feature inviting the orthogenetic explanation is the directive character of evolutionary trends, their apparent persistence towards a predetermined goal. But on reflection this too is seen to be not only explicable but expected on a selectionist viewpoint… It is impossible on orthogenetic principles to explain why one group should contain... the tendency to show marked divergent radiation and another comparable group should not, why one should form twice or four times as many orthogenetic trends as another.” (Pg. 497-498)
He suggests, “a progressive mutational change in the speed of processes controlled by rate-genes affords a complete formal explanation of many paleontological data… It further affords an explanation certainly of most and probably all cases of so-called reversal of dominance…. It also helps to understand the presence, the persistence, and the variability of vestigial organs… Consideration of the threshold-effect of any genes acting as rate-controllers for vestigial organs will also show that such organs must be unusually variable…” (Pg. 529-530)
He notes that “The question of evolutionary or biological progress remains… [One] type of objection consists in showing that many processes of evolution are not progressive in any possible sense of the word, and then drawing the conclusion that progress does not exist… A variant of this objection is to draw attention to the numerous cases where evolution has led to degeneration … of form and function, as in tapeworms… it is asked, can the evolutionary process be regarded as progressive if it produces degeneration?... This, however, is an elementary fallacy. The task before the biologist is not to define progress a priori, but to proceed inductively to see whether he can or cannot find evidence of a process which can legitimately be called progressive. It may just as well prove to be partial as universal… Thus evolution may perfectly well include progress without being progressive as a whole.” (Pg. 556-558)
He summarizes, “The distinguishing characteristics of dominant groups all fall into one or other of two types---those making for greater control over the environment, and those making for greater independence of the environment. Thus advance in these respects may provisionally be taken as the criterion of biological progress.” (Pg. 562) But he cautions, “We must, however… beware of subjectivism and of reading human values into earlier stages of evolutionary development… only biological values can have been operative before man appeared.” (Pg. 566) He concludes, “Progress is all-round biological improvement. Specialization is one-sided biological improvement: it always involves the sacrificing of certain organs or functions for the greater efficiency of others.” (Pg. 567)
Perhaps surprisingly (Huxley was a leader in the Humanist movement), he observes, "there are other faculties, the bare existence of which is as yet scarcely established… I refer to telepathy and other extra-sensory activities of the mind, which the painstaking work of Rhine, Tyrrell and others is now forcing upon the scientific world as a subject demanding close analysis.” (Pg. 574)
This book will be “must reading” for anyone studying the development of modern evolutionary theory.
English evolutionary biologist Julian Huxley (1887-1975; Thomas Henry Huxley---‘Darwin’s bulldog’---was his grandfather) wrote in the Preface to this 1943 book, “Even among professional zoologists the modern conception of natural selection and its mode of operation is quite different from that of Darwin’s day, but much of the research on which the changed outlook is based is so recent that the new ideas have not spread far. The idea of evolutionary progress, on the other hand, has been undeservedly neglected. Thus it seemed to me valuable to attempt to give a broad account of the two concepts and their relation to each other.”
He explains in the first chapter, “already we are seeing the first-fruits in the re-animation of Darwinism. By ‘Darwinism’ I imply that blend of induction and deduction which Darwin was the first to apply to the study of evolution.” (Pg. 13) He continues, “a struggle for existence… for survival, must occur… in Darwin’s time… the subject of inheritance was still very obscure… the principles of genetics had not yet emerged… there must be a differential survival of different types of offspring in each generation… SOME variation is inherited: and that fraction will be available for transmission to later generations… The term ‘Natural Selection’ … [has] two rather different meanings. In a broad sense it covers all cases of differential survival; but from the evolutionary point of view it covers only the differential transmission of inheritable variations.” (Pg, 15-16)
He continues, “The raw material for evolution by natural selection falls into two categories---mutation and recombination. Mutation …. alters the nature of genes. Recombination… though it may produce quite new combinations… only juggles with existing genes.” (Pg. 21) He goes on, “Mendelism is a theory of heredity… [It] is now … an essential part of the theory of evolution. Mendelian analysis … together with selection, explains the progressive mechanism of evolution.” (Pg. 26) He summarizes, “Neither mutation nor selection alone is creative… in evolution; but the two in conjunction are creative.” (Pg. 28)
He notes, “the demonstration that small mutations occur and can serve as the raw material on which natural selection may act to effect gradual evolutionary change, does not mean that this is … the only type of evolutionary change possible… species may be formed abruptly, and other large variations are known to … serve, in some cases, as building-blocks of evolutionary change.” (Pg. 41)
He outlines, “From the standpoint of the mode of action of natural selection, species… fall into two contrasted categories… we have those in which natural selection … merely acts upon the species as given, in competition with its relatives…. In which character-modification is abrupt and initial. On the other hand, we have those forms in which character-modification is gradual… These include … forms in which the separation of groups occurs by geographical, physiological, or ecological isolation, but also those in which the initial separation is genetic but involves no visible differentiation… groups separated ecologically will be exposed to a considerable intensity of selection to adapt them fully to their different modes of life.” (Pg. 384)
He adds, “If Darwin were writing today he would call his great book ‘The Origins,’ not ‘The Origin,’ of Species.” (Pg. 387)
He states, “in general, the preponderance of degenerative (loss) mutation will result in degeneration of an organ when it becomes useless and selection is accordingly no longer acting on it… constitutional preadaptation acts … [by] restricting inhabitants of specialized habitats … to forms with some definite predisposition to the peculiar mode of life involved… a constitutional preadaptation towards cold-resistance has led to certain… plants being able to survive in higher latitudes… various marine Crustacea … are able to tolerate waters of low salinity much more readily at high than at low temperatures… [Richard] Goldschmidt… has suggested that preadaptation may play a rather different role by means of large mutations giving what he styles ‘hopeful monsters,’ which can then serve as the starting-point for quite new evolutionary trends… I do not propose to discuss these rather revolutionary views… I disagree with them in general… However, even if we dismiss Goldschmidt’s views as unproven or unnecessary, preadaptation of various kinds has clearly played a not inconsiderable role in evolution.” (Pg. 455-457)
He asks, “How has adaptation been brought about? Modern science must rule out special creation or divine guidance… [Henri] Bergson’s ‘elan vital’ can serve as a symbolic description of the thrust of life during its evolution, but not as a scientific explanation… Bergson was a writer of great vision but with little biological understanding, a good poet but a bad scientist… Modern biology … also repudiates Lamarckism [the ‘inheritance of ACQUIRED characteristics’].” (Pg. 457-459) Later, he adds, “when numerous adaptations are shown to be incapable of Lamarckian explanation… [to] postulate Lamarckism to account for … others … would be to sin against the economy of hypothesis… William of Occam’s razor.” (Pg. 464) He continues, “Most biologists also look askance at orthogenesis [i.e., that organisms have an innate tendency towards some goal]… This is too much akin to vitalism and mysticism for their liking; it removes evolution out of the field of analyzable phenomena; and it… goes contrary to Occam’s razor. (Pg. 465)
He continues, “There can be little doubt that the apparent orthogenesis which pushes groups ever further along their line of evolution until, as with size in some mesozoic reptiles and armor in others… they are balanced precariously upon the edge of extinction… is due, especially in it is later stages, to be … induced by intraspecific competition. This conclusion is of far-reaching importance. It disposes of the notion… that all man need to do to achieve further progressive evolution is to adopt the most thoroughgoing competition… But we now realize that the results of selection are by no means necessarily ‘good,’ from the point of view either of the species or of the progressive evolution of life. They may be neutral, they may be a dangerous balance of useful and harmful, or they may be definitely deleterious. Natural selection, in fact, though like the mills of God, in grinding slowly and grinding small, has few other attributes that a civilized religion would call Divine. It is efficient in its ways---at the price of extreme slowness and extreme cruelty. But it is blind and mechanical; and accordingly its products are just as likely to be aesthetically, morally, or intellectually repulsive as they are to be attractive. We need only think of … a brood of ichneumon-flies slowly eating out a caterpillar.” (Pg. 484-485)
He argues, “The only feature inviting the orthogenetic explanation is the directive character of evolutionary trends, their apparent persistence towards a predetermined goal. But on reflection this too is seen to be not only explicable but expected on a selectionist viewpoint… It is impossible on orthogenetic principles to explain why one group should contain... the tendency to show marked divergent radiation and another comparable group should not, why one should form twice or four times as many orthogenetic trends as another.” (Pg. 497-498)
He suggests, “a progressive mutational change in the speed of processes controlled by rate-genes affords a complete formal explanation of many paleontological data… It further affords an explanation certainly of most and probably all cases of so-called reversal of dominance…. It also helps to understand the presence, the persistence, and the variability of vestigial organs… Consideration of the threshold-effect of any genes acting as rate-controllers for vestigial organs will also show that such organs must be unusually variable…” (Pg. 529-530)
He notes that “The question of evolutionary or biological progress remains… [One] type of objection consists in showing that many processes of evolution are not progressive in any possible sense of the word, and then drawing the conclusion that progress does not exist… A variant of this objection is to draw attention to the numerous cases where evolution has led to degeneration … of form and function, as in tapeworms… it is asked, can the evolutionary process be regarded as progressive if it produces degeneration?... This, however, is an elementary fallacy. The task before the biologist is not to define progress a priori, but to proceed inductively to see whether he can or cannot find evidence of a process which can legitimately be called progressive. It may just as well prove to be partial as universal… Thus evolution may perfectly well include progress without being progressive as a whole.” (Pg. 556-558)
He summarizes, “The distinguishing characteristics of dominant groups all fall into one or other of two types---those making for greater control over the environment, and those making for greater independence of the environment. Thus advance in these respects may provisionally be taken as the criterion of biological progress.” (Pg. 562) But he cautions, “We must, however… beware of subjectivism and of reading human values into earlier stages of evolutionary development… only biological values can have been operative before man appeared.” (Pg. 566) He concludes, “Progress is all-round biological improvement. Specialization is one-sided biological improvement: it always involves the sacrificing of certain organs or functions for the greater efficiency of others.” (Pg. 567)
Perhaps surprisingly (Huxley was a leader in the Humanist movement), he observes, "there are other faculties, the bare existence of which is as yet scarcely established… I refer to telepathy and other extra-sensory activities of the mind, which the painstaking work of Rhine, Tyrrell and others is now forcing upon the scientific world as a subject demanding close analysis.” (Pg. 574)
This book will be “must reading” for anyone studying the development of modern evolutionary theory.
Displaying 1 of 1 review