Science in Christian Perspective

Impact of the Rediscovery of Genetics on the Concept of Variation in Darwinian Theory

JOHN E. LOTHERS, JR.
Department of Biology
Covenant College
Lookout Mountain, TN

From: JASA 37 (December 1985): 205-210.

Development Of an evolutionary paradigm was delayed for several decades after publication of Darwin's The Origin of Species. One of the causes for the delay was the rediscovery of genetics with a consequent awareness that there were limitations on variation. The rediscovery led to conflicts which further delayed development of a consensus. Conflicts between the concept of discontinuous variation of the geneticists and the concepts of continuous variation and natural selection of the paleontologists, biometricians and other evolutionary biologists developed and remained unresolved into the 1920's and 1930's. Organisms were not as plastic as had been thought in Darwin's time. It is suggested that lack of knowledge of genetics, when evolutionary theory was being developed, might have contributed to its acceptance and affected its formulation.

"It could be argued that nothing approaching a 'Darwinian paradigm' became established until the 1930's, and even that paradigm was Darwinian only in a very loose sense."¹ This article will examine some of the causes of the long delay in development of a consensus on evolution particularly emphasizing the impact of the rediscovery of Mendelian genetics which showed that there were limits on capacity for variation. What effect did the rediscovery of laws of heredity and limits on variation have on a concept of evolution which was vague about limits (which actually included no limits) on variability? Charles Darwin expressed his view on potential for variation as follows:

What is the limit to the possible amount of variation of any part or quality, and, consequently is there any limit to what selection can effect? These questions can not be positively answered, but it is certain that we ought to be cautious in answering them by a negative²

The fluctuating and, as far as we can judge, never ending variability of our domesticated productions, the plasticity of almost their whole organization, is one of the most important lessons which we learn from the numerous details given in the earlier chapters of this work.³

An erroneous understanding of heredity was not limited to Darwin. No other prominent 19th century scientist other than Mendel understood it either. Carl von Naegeli and Kerner von Marilaun

... were far too busy studying highly variable genera which showed promise of evolving in front of their eyes to stop and examine the laws of inheritance.... The neglect was thus in part a result of assuming that the study of constant forms will not lead to the source of variation, and in part [due] to the simple fact that the cytologists had yet to discover the material basis for Mendelism and for a concept of heredity far more non-variable than any Darwinian was prepared to accept.⁵

For a further discussion of why Mendelism was not understood prior to 1900 see Jenkins.⁶ The most obvious gap in the theory of evolution was the almost complete ignorance of the laws of inheritance.' Some general biology texts and lectures fail to communicate the problems for evolution that followed rediscovery of genetics in 1900, and merely say that genetics supported the evolutionary view, (Knowledge of genetics did, of course, help with the problem of swamping of variations by the much more numerous individuals not showing the variation, but this is the only effect of genetics that is normally mentioned.) This article is intended to provide a balance on this issue.

Even before rediscovery of genetics a number of problems had developed in evolutionary theory. Some of these will be examined to provide a context for the conflicts which were to follow.

Problems That Had Developed in Evolutionary Theory by 1900 Prior to Rediscovery of Genetics

Problem of Swamping Effects

Abnormal variations ("sports") were said to be swamped by breeding of the individuals possessing them with the much larger number of individuals having unchanged characteristics.⁸ In response it was suggested that there might be simultaneous mutation in the same direction so both individuals involved in a mating might have new characteristics, This suggests either a Lamarckian response to the environment or an internal orthogenetic drive (evolution in a certain direction).⁹ In either case fluctuating, fortuitous individual variation would have to be abandoned and with it much of the importance of natural selection.¹⁰

Neo-Lamarkism began in the United States in the 1860's. Two such Lamarkian views were those of 1) Cope, who thought characteristics were acquired by movement of parts,¹¹ and of 2) Hyatt, who believed that characters belonging to adults become embryonic in the next higher species.¹² Cope thought that characteristics of the vertebrate skeleton were acquired through motion or use by gradual accretions of modifications. Darwin had himself prepared the way for a Lamarkian position. He held the environment responsible for change in domestic productions through its effect on the reproductive organs and spoke of use and disuse.^13,14 As pointed out previously, Darwin's hypothesis of pangenesis was consistent with a Lamarkian interpretation Darwin's reaction to the problem of swamping effect-, included "his increasing attribution of variation to such Lamarkian factors as the direct action of environmental conditions and the inherited effects of habit use and disuse."¹⁵ An example of orthogenesis as expressed by Nageli was that "life, once formed from lifeless matter, contained an urge driving towards even higher forms ... towards perfection.¹⁷

The mutation theory of Hugo de Vries was also a way of solving the difficulty of swamping.¹⁸ If the mutant form was infertile with the parent type it could not be swamped through back crossing.

Disenchantment with the Speculation Of Morphological Darwinians

Some biologists including William Bateson didn't like the speculation that was evident in the thinking of the Darwirlians. Bateson said ... if,' say we with mucy. circumlocution,'the course of nature followed the line, we have suggested, then, in short, it did.' That is the sum of our argument."¹⁸ According to Raymond Pearl,

In the minds of an astonishingly large number of people ... it is precisely the same thing to show that something logically must be so as it is to show that it is so .... As everyone knows, this attitude led practically to the intellectual bankruptcy of the whole evolution theory in the late nineties .... ¹⁹

Polarization into Opposing Viewpoints by the Turn of the Century

Conflict between Discontinuous and Continuous Variation

Darwin and his followers refused to admit the possibility of evolution of species by abrupt changes. Wallace and other followers insisted upon the exclusive efficiency of selection exercised upon small individual

John E. Lothers, Jr., is professor of biology at Covenant College, Lookout Mountain, TN. His teaching areas include genetics, evolution, embryology, microbiology, nutrition, vertebrate histology, history of biology, and taxonomy of the vascular plants, He received his MS from Kansas State University in biochemistry and PhD from The University of Kansas in zoology with emphasis in genetics.

This was closely related to the conflict between discontinuous and continuous variation since natural selection was thought to act on continuous variation but was thought to be unnecessary with discontinuous variation. Natural selection had been used to excess even in Darwin's time, some people having said it induces variability.²⁶ By the end of the 19th century there was a distinct reaction against selection. Some eminent biologists felt that mutation had made natural selection unnecessary. However, between 1910 and 1920 belief in natural selection was revived.²⁷

Conflict between Biometricians and Mendelians

"Three separate modes of evolutionary explanation led into the 1920's that were distinct in their approaches: the genetic, the naturalist, and the biometric or statistical."²⁸ A brief history of the conflict between the biometricians and Mendelians follows. The biometricians, Pearson and Weldon, chose at first to fight Mendelism as a trivial exception to biometrical heredity with which it could not be made to conform.²⁹ Weldon realized that discontinuity in heredity meant an end to that continuity in variation upon which the biometrical school was founded.³⁰ So the first step in the Mendelian controversy was provided by Weldon's belittlement of Mendel's work in the first volume of Biometrica. Bateson's rejoinder came in the form of a small book in 1902. It was delayed since he first set to work to repeat Mendel's experiments. In addition struggling geneticists at the time had few periodicals available in which to publish their articles.

To Bateson as to others Darwinism was overplayed and suspect. In contrast Mendel offered an arithmetically simple and biologically successful approach ... Darwinism, biometry, and continuous variation were out. Mendelism, simple arithmetic and discontinuous variation were in.³¹

Integration of opposing viewpoints could not be expected from Bateson and Pearson. Bateson criticized what he felt was careless experimental technique in Pearson's work. No artificial crosses were undertaken. The flowers were left uncovered, open to the insects which may introduce the pollen of any other flower which they happen to carry.³² Jennings said that biometricians that devote themselves to careful biological investigation fall away from Pearson.³³

To naturalists, paleontologists, and many others it seemed impossible that the large mutations of the geneticists could give rise, under the action Of selection, to changes of the type they could observe in evolving faunas and floras.

Support from Other Scientists

Support came rather soon from other workers using varying experimental material. East, who worked with maize, said that corroborative evidence had been received from so many lines that it could hardly be doubted that the main points of the hypothesis were correct.³⁶ Jennings showed that selection for size in Paramecium comes to the end of its action.³⁷

A very large share of the apparent progressive action of selection has really consisted in the sorting over of pre-existing types so that it has by no means the theoretical significance that had been given to it.³⁸

Pearl selected for fecundity in the fowl, getting high and low lines.³⁹ This work expanded the evidence for limit on selection to "non-selfed" organisms. Pearl wrote:

It seems to me that it has never been demonstrated that continued selection can do anything more than (1) isolate pure biotypes from a mixed population which contains individuals of different hereditary constitution in respect to the character or characters considered, [or] (2) bring about and perpetuate ... certain combinations of hereditary factors which would never (or very rarely) have occurred and would have been lost in the absence of such systematic selection. . . . ⁴⁰

Continued selection in pure lines has been wholly negative as reported by various workers for cereals (including wheat and oats), hydra, Aphis (an aphid), lentils, peas, soybeans, and lupines.⁴¹

Opposition to the pure line theory came particularly from three critics. 12 It came from Pearson and Harris because Johannsen's work shows the "utter untenability of the correlation coefficient as a measure of heredity._" ⁴³  The third critic, Castle, said he selected through sixteen generations for size of the hooded pattern in the coat of rats.⁴⁴ Variation occurred in the length of the pigmented hood and the width of the back stripe. Castle wrote that

In this case selection had modified steadily and permanently a character unmistakenly behaving as a simple Mendelian unit."⁴⁵

The plus and minus series have from time to time been crossed with the same wild race. Each behaves as a simple 3:1 ratio among the grandchildren.⁴⁶

Castle stated further:

A single variable genetic factor was concerned in the original hooded race, that a changed condition of this same factor was produced in the minus race and another changed condition in the plus race and a third appeared in the mutant race. All are allelomorphs of each other and of the nonhooded or self condition found in wild rats. . . "

In an article in The American Naturalist in 1917, Hagedoorn and Hagedoorn commented: "It is well known that Dr. Castle counts among the few last geneticists who still believe that the genes themselves are modified by selection."⁴⁸

In 1919 Castle published a correction:

I thought two years ago that I had evidence that a single gene had changed in the course of a selection experiment .... I now find this view rendered untenable by further experiments ... the supposed changes in a single gene are more probably due to changed residual heredity, which very likely may consist wholly of other 'modifying genes.⁴⁹

The further experiments he performed were to cross plus and minus hooded races with a third race and recover hooded characters as a recessive in the F2 generation. The hooded pattern in the two selected races became identical when the modifiers were thus removed.⁵⁰ However, Castle still criticized most geneticists for extending the pure line theory to crossfertilizing forms.⁵¹ Harris, another of the three abovementioned critics of the pure line theory, referred to it as follows, " . , . the pure line theory ... the rank vines which have grown from the nineteen bean seeds which johannsen planted in 1901.⁵² Two arguments he used against pure line theory were (1) characters that are not inherited can't be taken to prove that selection is ineffective (Maybe seed weight isn't inherited.); and (2) improvement for any single character can't be said to be unlimited. Because a wheat plant "can not be made to yield all grain and no stubble, we are told that selection can only isolate already existing types."

Some general biology texts and lectures fail to communicate the problems for evolution that followed rediscovery of genetics in 1900, and merely say that genetics supported the evolutionary view.

Some biologists expressed reservations about the Darwinian Theory although not about evolution. Conklin said

. . . the experimental study of genetics has been a little disappointing. We had supposed that organisms would be more tractable, more willing to evolve than we find them. The older view that organisms were plastic and could be molded 'while you wait' now reminds one of the view of certain childless theorists, that children are. plastic clay in the hands of parents or teachers; both of these views neglect the fact that the living organism, delicate and responsive beyond compare, is still wonderfully strong, stable and stubborn. So far as the factors of evolution are concerned experimental study has been a weeding out process, and at times it seems that nothing will be left.⁵³

In a 1914 address Bateson said

The outcome (of evolutionary aspects of genetic research) as you will have seen is negative ... destroying much that 'till late passed for gospel ... We are just about where Boyle was in the seventeenth century. We can dispose of alchemy but we can not make more than a quasi-chemistry. We are awaiting our Priestly and our Mendeleeff.⁵⁴

And in a 1922 address Bateson said that faith had given place to agnosticism. Though our faith in evolution stands unshaken we have no acceptable explanation of the origin of species.⁵⁵ Not all scientists took as strong a position as Bateson, but views similar to his were widely held. D. H. Scott, a botanist, said

In our present total ignorance of ... the causes of variadon ... we can form no clear idea of material on which selection has had to work and we must let the question rest ... all is again in the melting pot.⁵⁶

M. Caulbery, an exchange professor at Harvard, said

The data of Mendelism embarrass us also very considerably. All that it shows us, in fact, is the conservation of existing properties. Many variations which have seemed to be new properties are seemingly traced to previously unobserved combinations of factors already existing.⁵⁷

Many of the modern ideas about sources of variation had been suggested before 1920. In a 1917 article in The American Naturalist three kinds of variability were given: (1) modification, the non-inheritable effect of the non-genetic developmental factors, (2) real inheritable variation caused by mutation or loss of genes, (3) real inheritable variation caused by recombination of genes.⁵⁸ Modifying genes, which would later be the basis for synthesis and resolution of some of the conflict (particularlv that between continuous and discontinuous variation), had been suggested by the 1920's. Castle had mentioned them in a paper cited earlier. T. H. Morgan⁵⁹ in the United States and the Chetverikov School in Russia also mentioned them.⁶⁰ Modifying genes permitted small genetic changes so that continuous variation (as well as discontinuous) could be explained genetically. However in the early 1920's the study of evolution seemed to have reached a blank wall bevond which for the moment advance was impossible."⁶¹

Thus the magnitude of the problem was such that over twenty years after the rediscovery of genetics the tension remained unresolved. Genetics bad not been so clearly and simply a buttress for evolutionary theory as has been suggested in some general biology text books and by some lecturers. An example of a statement found in a general biology book follows:

The weight of scientific evidence over the past 100 years is strongly supportive of Darwin's basic precepts, and such areas of biological specialization as biogeography.... genetics, and molecular biology, have provided especially strong support.⁶²

In a 1973 debate on evolution William V. Mayer said "In the meantime [since 1860] ... the evidence on which the theory of evolution rests has been buttressed by genetics, biochemistry, and whole new scientific fields unknown over a century ago. "63 Over-simplification, however, can lead to erroneous impressions. Theistic scientists need not feel that the evidence compells them to echo such statements.

It would be interesting if we could know what might have happened if genetics had been understood before Darwin's publication. Was the theory of evolution accepted in the 19th century primarily because of convincing scientific evidence or might it have been accepted because of other contributing factors? Perhaps one contributing factor could have been the lack of understanding of heredity when the issue was being discussed.

Some of the other factors, which are outside the scope of this paper and hence only mentioned here, might include

(1) Limitation of explanations to only two: monophyletic macroevolution, and the then prevalent fixity of species concept, with evidence for change being taken as evidence for the former.

(2) Creation alternatives rejected because of a metaphysical commitment. "Once it [our metaphysical position] has been adopted it will shape, rather than be shaped by, our scientific or common-sense observations."⁶⁴

(3) Creation alternatives rejected because anything supernatural is not considered science. Failure to see the difference between operation science (where, according to Thaxton et al., "appeal to God is quite illegitimate since by definition God's supernatural action would be willed at His pleasure and not in a recurring manner⁶⁵) and origin science, where hypotheses are not testable or falsifiable, has led to "excluding the divine from origin science as well as from operation science."⁶⁶ This viewpoint is, no doubt, more fully developed now than it was during the 19th century.

The idea that life arose by chance from energy striking a primordial atmosphere is now being seriously questioned. In The Mystery of Life's Origin Thaxton et al. write

A major conclusion to be drawn from this work is that the undirected flow of energy through a primordial atmosphere and ocean is at present a woefully inadequate explanation for the incredible complexity associated with even simple living systems and is probably wrong "

A theistic position would reject the idea that the increased complexity accompanying evolutionary change from a primordial chemical atmosphere up to the first cell, and on to all the complex organisms, occurred by chance without divine guidance. Evolution by chance could be compatible with a deistic position but not a theistic one. Perhaps monophyletic macroevolution per se may also be questioned. Its acceptance could have been due in part to the sequence of historical events rather than to clear scientific evidence. The formulation of the theory and extent of change postulated would most likely have been affected by an understanding of genetics and limits on variation. The extent and direction of the subsequent refining of the theory could also have been influenced by the strength of the commitment to the theory as originally expressed.

¹Greene, John C. Science, Ideology and World View, Berkeley, University of California Press, 1981, p. 53

²Darwin, Charles, The Variation of Animals and Plants under Domestication, New York, D. Appleton and Co., 1898, Vol.11, p. 228. See also Darwin, Charles The Origin of Species, New York, Everyman's Library, Dutton, 6th Ed., 1928, p. 445

⁵0lby, Robert C. Origins of Mendelism, New York, Schocken Books, 1966, p. 142

⁷Carter, G. S. A Hundred Years of Evolution, London, Sidgwick and Jackson, 1957, p. 102

⁸Jenkin, Fleeming, "The Origin of Species," The North British Review, 46:277- 318, June 1867. Quoted in Hull, David L., Darwin and His Critics, Cambridge, MA, Harvard University Press, 1973, pp, 319-320

⁹Eisely, Loren. Darwin's Century, Carden City, New York, Doubleday Anchor Books, 1958, p. 210

¹⁰Willis, J.C. The Course of Evolution, Cambridge, Cambridge University Press, pp. 5,165-166,1940. Quoted in Eiseley, Loren, op cit., p. 210

¹¹Cope, E.D., "The Present Problems of Organic Evolution," Science N.S., 2:124-126,1895, p. 124

¹²Pfeifer, E.J. "The Genesis of American Neo-Lamarekism," Isis, 56:156-167, 1965, p. 156

¹³Darwin, Charles. The Origin of Species, London, J. M, Dent & Sons, 1928, p. 130

¹⁴ Darwin, Charles. The Variation of Animals and Plants under Domestication, op cit., p. 416

¹⁵Vortzimmer, Peter J. Charles Darwin: The Years of Controversy, The Origin of Species and It's Critics 1859-1882, Philadelphia, Temple University Press, 1970, p. 126

¹⁶Radl, Emmanual. The History of Biological Theories, London, Humphrey Milford, Oxford University Press, 1930, p. 225

¹⁷Allen, Garland E. "Hugo de Vries and the Reception of the Mutation Theory," Journal of the History of Biology, 2:55-87, 1969, p. 71-72

¹⁸Bateson, William. Materials for the Study of Variation, London, MacMillan & Co., 1894, Preface, pp. v-vi

¹⁹Pearl, Raymond. "The Selection Problem," The American Naturalist 51:6591, 1917, pp. 67-68

²⁰Cox, Charles F., "Charles Darwin and the Mutation Theory," The American Naturalist, 43:65-91, 19N, p. 65

²³Bateson, William. Mendel's Principles of Heredity, Cambridge at the University Press, 19W, p. 289

²⁴Osborn, Henry Fairfield. "The Continuous Origin of Certain Unit Characters as Observed by a Paleontologist," The American Naturalist 46:185-206, 1912, P. 193

²⁶AIlen, Garland E. "Thomas Hunt Morgan and the Problem of Natural Selection," Journal of the History of Biology, IA13-139,1968, p. 114

²⁷The Encyclopedia Americana, International Edition, Vol.10, New YorL Americana Corp., 1968, p. 609

²⁸Adams, Mark B. "Towards a Synthesis: Population Concepts in Russian Evolutionary Thought 1925-19M," Journal of the History of Biology, 3:107-129,1970, pp. 108-109

²⁹Mather, Kenneth. "The Progress and Prospect of Biochemical Genetim" in L.C. Dunn (ed.), Genetics in the 20th Century, New York, The MacMillan Co., 1951, P. 113

³³Jennings, H.S. "Experimental Evidence on the Effectiveness of Selection,The American Naturalist, 44:136-145,1910, p. 143

³⁴Joharmsen, W. "Heredity in Populations and Pure Lines," 1903, in Petersj.A-. Classic Papers in Genetics, Englewood Cliffs, N.J., Prentice Hall, 1959, p, 25

³⁵Peters, J.A., Classic Papers in Genetics, Englewood Cliffs, N.J. Prentice Hall. 1959, p. 20

³⁶East, E.M. "The Genotype Hypothesis and Hybridization," The American Naturalist, 45:160-174, 1911, p. 161

³⁷ Jennings, H.S. "Heredity and Variation in Simplest Organisms," The Amer(can Naturalist, 43:321-337,19N, pp. 33"31

³⁸Jennings, H.S, "Pure Lines in the Study of Genetics in Lower Organisms," The American Naturalist, 45:79-89, 1911, p. 88

³⁹Pearl, Raymond, "Inheritance of Fecundity in the Domestic Fowl," The American Naturalist, 45:321-345,1911, pp. 322-323

⁴⁰Pearl, Raymond. "The Mendelian Inheritance of Fecundity in the Domestic Fowl," The American Naturalist, 46:697-711, 1912, p. 711

⁴¹Pearl, Raymond, "The Selection Problem," The American Naturalist, 5L%91, 1917, p. 84

⁴²East, E.M. "The Mendelian Notation as a Description of Physiological Facts," The American Naturalist, 46:633-655, 1912, p. 646

⁴⁴Castle, W.E. "The Beginnings of Mendelism in America," in L.C. Dunn (ed.), Genetics in the 20th Century, New York, The MacMillan Co., 1951, p. 71

⁴⁵Castle, W.E., "The Inconstancy of Unit Characters," The American Naturalist, 46:352-362, 1912, p. 356

⁴⁸Hagedoorn, A.E. and Hagedoorn, A.L. "New Light on Blending arid Mendelian Inheritance," The American Naturalist, 51:189-192, 1917, p. 189

⁴⁹Castle, W.E. "Piebald Rats and Selection, A Correction," The American Naturalist, 53:370-376,1919, p. 370

⁵³Conklin, Edwin G, "Problems of Evolution and Present Methods of Attacking Them," The American Naturalist, 46:121-128,1912, p. 128

₅₄ Bateson, William. "Address of the President of the British Association for the Advancement of Science," Science, 40:287-302, 1914, pp. 301402

⁵⁵Bateson, William. "Evolutionary Faith and Modern Doubts," Nature London, 109:553-556, 1922, p. 556

⁵⁷Caullery, M. "The Present State of the Problem of Evolution," The Smithsonian Institute Annual Report, Washington D.C., Government Printing Office, 1916, p. W

⁵⁸Hagedoorn, A.C. and Hagedoorn, A.L. "Rats and Evolution," The American Naturalist, 51:385-418,1917, p. 393

⁶⁰Adams, Mark B. "The Foundation of Population Genetics: Contribution of the Chetverikov School 1924-34," Journal of the History of Biology, 1:23-39, 1968, p. 32

⁶³Mayer, William V. "Evolution: Theory or Dogma?", Debate, National Science Teachers Association Audio Tape Series, E19, Current Information Association, Inc., 1973

⁶⁴Hein, Hilde. On the Nature and Origin of Life, New York, McGraw-Hill, 1971, p~ 93. Quoted in Thaxton, Charles B., Bradley, W.L., and Olsen, R.L., The Mystery of Life's Origin: Reassessing Current Theories, New York, Philosophical Library, Inc., 1984, p~ 207

⁶⁵Thaxton, Charles B., Bradley, W. L., and Olsen, R. L. The Mystery of Life's Origin: Reassessing Current Theories, New York, Philosophical Library, Inc., 1984, p. 203