Science in Christian Perspective
THE SCIENCE OF HEREDITY AND THE SOURCE OF SPECIES*
From: JASA 1
A paper presented at the third annual Convention of the American Scientific Affiliation at Calvin College, Grand Rapids, Michigan, September 2, 1948.
A great geneticist has admitted that "No individual can claim such a mastery of all facts pertaining to evolution to enable him to present 1 a full discussion of the facts, laws and theories of evolution. This appears to me to be especially true of the bearing of the science of heredity on evolution. Therefore an attempt will be made to answer only one question, "To what extent have species changed into other species?"
Some species appear to have descended from others. If two species can be crossed, and living offspring be produced, there is proof of compatible germ cells from the two species. The obvious source of this hereditary material is descent from a common ancestor.
The birds of the eastern United States which hybridize readily are the Goldenwinged Warbler and the Blue-winged Warbler. Their hybrids are called Lawrence's Warbler if there is a black throat, and Brewster's Warbler if there is not. The hybrids show the characteristics of the parents segregated in the offspring. A typical Lawrence's Warbler has a black throat from the Golden-winged parent but has yellow underparts like the Blue-winged ancestor. Similarly, upper parts, wing bars, and ear patches are typical of one parent or the other. Because the hybrids do combine traits of both parents, it is probably that at some past date the two parental types came from one type. To be sure, this transition was not observed; surely each species could have been created separately, even though they now interbreed. However, evidence from fruit flies which indicates that a species is now in the process of subdivision into two major groups indicates that the idea of the derivation of the two warblers from common ancestry is the correct explanation.
A species now undergoing subdivision is Drosophila pseudoobscura. There are two races, A and B which differ from each other, not in any observable external appearance but in the arrangement of genes on the chromosomes. (Genes are the units of heredity in cells arranged serially on rod-like bodies called chromosomes.) The genes in one race are in a certain order; in the other race, some of the genes are inverted.2 The races are told apart by breeding tests. Race A produces fertile offspring when mated with Race A, but when mated with Race B, sterile male offspring are produced. Here is the indication of the subdivision of the species. If the two races thus formed were to have visible character differences, a classifier would be justified in concluding variations of the chromosomal arrangements. In the third chromosome"....twenty-one different sequences have been recorded.',3 Any subsequent rearrangement may produce a character difference, or mutations (changes in the genes) may do so; then race A will be obviously distinct from race B and two species will have been observed to have arisen from one species.
In another species of Drosophila, melanogaster, character differences have appeared in large numbers. There are hundreds of kinds of flies possessing varied eye colors or wing sizes or body colors. Yet each kind crosses with any other one to produce fertile offspring. To produce two species from this single species,
1. Goldschmidt, Material Basis of Evolution, 1940, p. 3.
2. Dobzhansky, Genetics and the Origin of Species, 1941, p. 120.
there needs to appear a chromosomal change which will make those individuals possessing one trait sterile with those displaying a contrasting trait. If this occurs, character differences will have preceded reproductive differences in species alteration. On the other hand in Drosophila pseudoobscura, reproductive segregation has already preceded character differentiation.
In nature, the species of Drosophila actually differ in the ways seen in the flies already discussed. Chromosomal rearrangements occur within the members of one species; "....the chromosomal differences between species are identical in kind, if not in degree, with those found among races.and individuals.4 We readily accept the idea that the members of one species have a common ancestry even though they now have various chromosomal patterns; why should we hesitate to believe that flies now admittedly.separate species have a common ancestry if the differences between them are the kind that occur within one species?
Current biological thought holds that if any species gives rise to new species, then the conclusion may be drawn that the first living protoplasm could have been the ancestor of all kinds of life of the past and present. Reasoning from the probability that one species may become two, biologists conclude that one form of life may have given rise to all forms. As a creationist, I am willing to accept the origin of species from other species, called microevolution, but do not see the necessity for believing that a protozoon was transformed into a coelenterate, or a coelenterate into a round or segmented worm and similar macroevolutionary transformations up to man. "Experience seems to show, however, that there is no way toward an understanding of the mechanisms of macroevolutionary changes, which require time on a geological scale, other than through a full comprehension of the microevolutionary processes observable within the span of a human lifetime and often controlled by man's will. For this reason we are compelled at the present level of knowledge reluctantly to put a sign of equality between the mechanisms of macro- and microevolution, and, proceeding on this as sumption to push our investigations as far ahead as this working hypothesis will permit."5
Hereditary studies are incapable of establishing the assumed connection between all types of life. A university geneticist in a recent lecture remarked, "The higher categories and the problems there presented are a good ways from the field where genetics can make a direct contribution." Crosses can be made between species and between genera, and only infrequently between animals of greater distinctiveness. Because members of categories as widely separated as classes have not been crossed, there is no information about the similarities and differences in the genes of the members. We cannot put genes from two classes into one hybrid; birds and reptiles will not cross; we cannot therefore prove that the two could have come from one. The evolutionist speculates that somehow it could have happened; the creationist follows the statements of the Scriptures which say that the original kinds were brought forth by the command of God.
Notice some of the difficulties there would be in producing coelenterates from protozoa. A single celled animal would have to become many celled. These cells must be arranged into two layers, perhaps by the inpushing of one side of a hollow ball of cells. The inner cells acquire contractile fibers.at their bases. Certain outer cells produce stinging capsules. The whole mass becomes arranged into body and tentacles. Only in imagination can there be found hereditary changes capable of producing all of these advances which must have occurred if members of one phylum (major group) were to change into members of another phylum. The evolutionist believes that in the past there were mutations which could do this,alyhough
4. Ibid., p. 148.
5. Ibid., p. 12.
though they are not observed at the present time. The mutations which have been ,noted have altered organisms within a limited sphere. One of my professors said, "It would be a miracle that a mutation causing diversity would also cause convergence for an adaptive end."
A NEW THEORY
Neo-Darwinian geneticists conceive that a species changes slowly over many generations until it forms reproductively isolated populations which can be considered two species. But Goldschmidt has questioned the ability of mutations to produce specific differences." Microevolution by accumulation of micromutations - we may also say neo-Darwinian evolution - is a process which leads to diversification strictly within the species, usually, if not exclusively, for the sake of adaptation of the species to specific conditions within the area which it is able to occupy."6 Consequently, he has postulated a "new" kind of evolutionary mechanism, "Species and the higher categories originate in single macroevolutionary step as completely new genetic systems. The genetical process which is involved consists of a repatterning of the chromosomes, which results in a new genetic system.7 No mutations need to appear; all that is necessary is translocation8 of genes already present.
This process, he feels, will produce new species more rapidly than will happen by the slow accumulation of small mutations. Drosophila miranda and Drosophila pseudo-obscura are only slightly different in external appearance, but hybrids between the species are sterile. Studies of chromosomes reveal that the species are distinguished by different arrangements of similar genes. But Goldschmidt believes that a relatively small repatterning of chromosome will also produce considerable changes in appearance.10 This would avoid the difficulties of conceiving a gradual change from one species to another.11 Peculiar structures like the preformed exit in a plant for the insect living in it could have been formed at a single step. The imitation of a distasteful species of butterfly by an inoffensive one need not be by a gradual change over many generations but could have occurred between parents and offspring merely by rearrangement of the positions of the parts of chromosomes.
Goldschmidt emphasizes the large amount of change which may be produced in an offspring if a pattern rearrangement occurs in the germ cells of the parents. The development of the offspring is considerably altered. The wingpattern in a butter fly (Papilio dardanus) varies markedly depending on a few differences in genes. I is supposed that a rearrangement of these genes would produce as great or a greate difference. There would be "macroevolutidn by single large steps.,,12 However,, some of the new characters in fruit flies showing greatest change from normal char, acters, such as the appearance of four wings instead of two, are the result of simple mutations and not the result of pattern changes. Goldschmidt presumed that alterations occur in the germ cells and survive or perish there. They need not wait until they have produced visible characters and these characters have been selected for survival or death. The altered chromosomal pattern finally selected
6 Goldschmidt, 22. cit., p. 183-.
7 Ibid., p. 396.
8 A segment of a chromosome broken away and joined to another chromosome.
9 A segment of a chromosome broken out, turned around, and reattached to the same
10. Ibid., p. 209.
11. Ibid., p. 244.
12. Ibid., p. 331
affects a developing individual so strikingly that a decidedly different form is
produced. "The first bird hatched from a reptilian egg."13 Goldschmidt admits
"unfortunately no experimental attack upon this problem is at present
In a sentence summary, Goldschmidt's view is this: Slow accumulation of mutations over many generations will not change one species into another but the rearrangement of the genes will produce in the germ cells a pattern resulting in strikingly altered offspring which have become different species from the parents in a single step and are separated from them by a "bridgeless gap."
How has this idea been received by other geneticists? Dobzhansky notes that Goldschmidt's"... systemic mutations ... have never been observed. It is possible to imagine a mutation so drastic that its product becomes a monster hurling itself beyond the confines of a species, genus, family or class...The assumption that such a product may, however rarely, walk the earth, overtaxes one's credulity...."15 'Again "...the simplicity of Goldschmidt's theory is that of a belief in miracles.,16 Goldschmidt's chronosomal mutations, which are supposed to cause new species, are no different than those which occur within races of the same species. This is to say that Goldschmidt is offering nothing new; he is merely claiming more for a phenomenon than others do.
Single genetic changes may produce striking effects but the result is not likely to be a structure working harmoniously with other parts of the body. Slimmer holds that such "Jumps" as Goldschmidt believes in are not integrated with the rest of the animal. To get a bird from a reptile by ' any.other means than the slow accumulation of small changes, which is typical Darwinian evolution, would need "the direct intervention of the Creator Himself." "Only the wave of the magician's wand could have transformed the scales of a reptile forthright~into the plumage of a bird.'17
Another criticism of Goldschmidt's work is.that he maintains species to be dis
~crete.groups, separated by the bridgeless gap from other species. Bridgeless,
that is,.by any other mechanism than the rapid transformations which he thinks his
systemic mutat ' ions will produce. But species do not fit into rigid compartments.
"The lack of universality of such rigid subdivisions is what has ever since Darwin
been one of the main arguments in favor of evolution.'18 Certain,species can
easily be told apart. However, there..are some species that blend' into,' others; in
termediates are placed arbitrarily. Among flies of the genus Drosophila, some
types seem to belong to distinct species, other variants are classified according
to the opinion of the investigator into different species or merely into different
race's of the same species.19 Further, Dobzhansky and others point to the lack of
definition of species by Goldschmidt so that a reader has difficulty in detecting
where the "bridgeless gaps" between species exist. Consequently 11.. the main pre
mise of his theory is wholly unacceptable."20
It should be mentioned to the credit of both Goldschmidt and neo-Darwinians, like Dobzhansky, that the latter admits, "It must, nevertheless, be recognized that Goldschmidt's keenly critical knowledge has emphasized the weaknesses and deficiencies of the neo-Darwinian conception of evolution, which are numerous, as even
13. Ibid., p. 395. The statement was made by Geoffrey St. Hilaire.
14. Ibid., p. 334
15Dobzhansky., op.'cit., p. 53.
16. Dobzhansky, Science, Vol. 52, 1940,p. 358
17. Sumner, Science, Vol. 93, 1941, p. 522.
18. Dobzhansky, op. cit., p. 357.
19. Dobzhansky, Genetics and the Origfti of Species, 1941, p. 371.
partisans ought to have the courage to admit. It would seem that this fact alone obliges anyone interested in the modern evolutionary thought to read Goldschmidt's book."21 In my opinion, one is obliged to read Dobzhansky's excellent volume also and compare his handling of data with that by Goldschmidt.
The source of structures as complex as the eye has always been difficult to explain, "Here is one of the puzzles of evolution which appears to be still far from solution.,,22 Goldschmidt has listed nineteen different features which he challenges Darwinian evolutionists to explain "by accumulation and selection of small mutants."23 Mayr has admitted that "it is a considerable strain on one's credulity to assume that finely balanced systems such as the eye or a feather could be improved by random mutations."24
"The eye appears as if at a single jump from no definite previous form, and 'transitional stages are wholly conjectural'.,25 There are eight or more theories recounted in Walls' volume. None of these is corroborated by comparative anatomy, because no animals exist possessing the stages which should have preceded the eyes of the cyclostomes (the first vertebrates), which in all essentials are like mammalian eyes. What caused the lens to be formed from ectoderm at the same time the retina was developing from the nerve tube is a 'tantalizing mystery'.26
"The study of heredity provides practically no evidence for a type of genetic change capable of producing the transformation of any kind of simple light-sensitive structure into a complex organ of vision."27 A duplication of genes at one location on a chromosome of a fly will reduce the number of facets in a compound eye to a bar eye. Several eye color alterations have appeared but these are shades of red; .... "there has been no blue or green. In view of the frequency of mutation of eye color, one is led to suspect that blues and greens are absent because Drosophila is incapable of mutating in that way."28 A certain mutation produces an eyeless condition. Another gives an antennalike structure "instead of an eye or combined with a rudimentary eye.29 Not only is it difficult to see how mutations could improve the eye as it now exists, but also how they could even begin to form an eye in view of the fact that the known mutations of the eye are harmful to it. According to Walls, Froriep compared the origin of the eye to the birth of Athena full grown from the brow of Zeus. Because creation is the making of something without the necessity of a prototype, this abrupt appearance of the eye in vertebrates is in harmony with the Creation doctrine.
One modern scholar has seen the reasonableness of creation. ' 'Some people assume, entirely as a matter of faith, a Divine Creation of living substance. The only alternative seems to be the assumption that at some time in the dim past, the chance association of the requisite chemicals in the presence of favorable temperatures, moisture, etc., produced living protoplasm. In other words, if one subscribes
21. Dobzhansky, Science, Vol. 92, 1940, p. 358
22. Shull, Evolution, 1936, p. 161.
23. Goldschmidt, op. cit., pp. 6,7.
24. Mayr, Systematics and the Origin of Species, 1942. p. 296. 25. 26. 27.
25. Neal and Raud, Chordate Anatomy, 1939, pp. 395, 407.
26. Walls, The Vertebrate Eye, 1942, p. 108.
27. Mixter, A Christian View of the Origin of the Vertebrate Eye, Christian Medical Society News, May, 1947
28. Shull, op. cit., p. 123
29. Goldschmidt, op. cit., p. 327.
DR. MAC RAE: You have a man and woman that are tall and maybe they have a.
dwarf child or a midget; and a couple of midgets have a child and it is tall. That
is a striking change but it is entirely within our human species, and even if from
that a tall group, small dwarfs are born I and keep-on being dwarfs As long as they interbreed with the tall group, you wouldn't say it is a new species, would you?
DR. MONSMA: No, I wouldn't, but who is going to tell what somebody else's point of view is. Taking an example of two groups, one called 'clumpers' and thee other that they call 'splitters.' If you were a 'splitter,' you would call everything a new species; if you were a 'clumper' you wouldn't.
DR. KULP: There is another problem. You are attempting to use the criterion of breeding. That is fine until you get into the field of paleontology. Naturally when you get into paleontology, the question arises as to what makes a species. According to the average paleontologist, it is simply a question of a distinguishable difference. When his whim decides that there are enough more rings on a certain shell to make it distinguishable for purposes of classification, that is a species. He can't say anything about breeding when he is a paleontologist. The only thing he can tell you apparently in a very broad way is that mammals and birds are not found in the earliest structures you find invertebrate life, but in considerably later structures you find mammals and in the very uppermost sheet of paper on this whole stack of volumes, you find hominoid fossils, and in a very broad way, that is about all he can say.
MISS ERDMANN: I disagree with that. I think you are talking about the greater gaps of evolution when you talk about man and the invertebrates and if you talk about just down to the level of the invertebrate paleontology there are many instances where we have indisputable changes through a succession of strata in a given number of centimeters. In other words, say you have 100 centimeters in a certain bank some place exposed, and in the bottom layer of those however many layers are there, you find one type of an animal; then in the successive ascending layers which represent successively later periods of time, you have changes in this one type of animal, and then by the time you get to the top layer, you have something entirely different from what you started with at the bottom layer, obviously something has happened there, and subjectively or not they call it two different species; but we have this direct proof on a small scale that we do have indisputable changes.
DR. KULP: I would disagree that it was indisputable, on the basis that a slight change in temperature would gradually make any species migrate along the coast so it would maintain precisely the same condition from top to bottom, so you might merely be reporting changing conditions at that particular spot.
MISS ERDMANN: You can change the strata across the country; you can check on
DR. KULP: If you can trace it in two dimensions it becomes of more significance but the paleontologist cannot hurdle the ecological barriers up to the present time. Until we can get physico-chemical methods to determine solubility, temperature, and pressure of the deposition, we cannot determine whether the fossil is the same or whether it has changed. I think that may come in ten years, but at the present time it isn't indisputable. It is merely evidence that there has been that change.
DR. VOSKUYL: Shouldn't we wait for the next ten years: There is a number of you that have been sitting here for at least an hour and a half, and the next two papers do not look like bed-time stories, so let's have a five-minute recess at this time.