Science in Christian Perspective
Letter to the Editor
[on mutation] Reply
From: JASA 5
The article in the September, 1953 Journal of the A.S.A. by Larnmerts and Sinclair is commendable for stating their point of view on the amount of change which can be produced by mutations. It argues for very little change, but some of us feel that this is too limited a view and one that will make many evolutionary scientists believe that we do not even follow as far as biological facts lead.
The first point of disagreement is with the statement that Eohippus, the beginning of the fossil series, "differed from the modern horse in so many features that only by the use of a certain amount of 'scientific imagination' called deduction can one understand the reasons causing paleontologists to consider Bohippas as the ancestral type from which our modern horse evolved." On the contrary Eohippus was really a horse, and is connected by a series which shows gradual changes from it on up to present day horses. The continuity convinces most persons that the members of the series are related. And the fact that the most ancient member of the series has equine characteristics was stated forcefully by one of America's leading paleontologists and students of horses, G. G. Simpson, when he said, "Despite the great difference between Hyracotherlurn (Eohippus) and Equus, (the modern horse) most of the characters of the Equidae did not change appreciably throughout their history. Hyracotherium was already a vertebrate, a mammal, a placental, an ungulate, perissodactyl, a hippomorph, and an equid, which is a classificatory way of saying that the vast majority of its multitude of morphological characters were already the same as those preserved in Equus and in all equids as well as in many other more or less related animals".1 It seems clear to us, then, that Lammerts and Sinclair are wrong in eliminating Eohippus from the horses' ancestry.
Regarding another point of difference, less that is definite can be said. If a person does not follow the large body of facts and logic, all of which point to "the long periods of geological time postulated by geoloist," he is, in my opinion, bound by a prejudice in favor of a recent creation, and there is no value in discussing the rates of change produced by mutations. But let us assume that the geological ages are dated with the right order of magnitude. Then there has been time for Eohippus to change to Equus at the known rate of mutation. This was thoroughly discussed by Simpson in his work, Tempo and Mode in Evolution. Summar izing briefly his argument, we find the following: There would need to be 0.15 genera per million years, or it would take seven million years per genus. In the estimated 40,000,000 years since the Eocene. there is time for about six genera to be produced, which is suf. ficient to account for the horse series. (Note, Lammerts and Sinclair are inaccurate in saying, "According to the geologic time scale as generally accepted by geologists, approximately 1,000,000 years have elapsed since Eocene times.")
Simpson estimates there have been 15,000,000 generations between Eohippus and Equus. Notice that Patau's calculations showed that about 1,000,000 generations would suffice to establish a characteristic in 100% of the population, so the number of generations in the Eohippus-Equus line could have seen 15 successive mutations established which are affecting any one feature of the animal. There can also be mutations affecting other parts of the animal at the same time and this would allow, for example, 100 differences from Eohippus to be established in Equus, and each one of the 100 could have been produced in 15 stages each. This suggests that Eohippus could have become Equus during the time that there has been available and that by the mutation rate that has been determined.
Actually, how much difference is there between Eohippus and Equus? We quote Simpson, "If the change in any one character from Hyracotherium to Equus is divided into 300 steps, these steps are almost imperceptibly small and are almost incomparably less than the amount of intragroup variation at any one time." If one can see so much variation within one generation, how can one say that "the many differences .between Eohippus and the modern horse could hardly have occurred since Eocene time?"
1 Simpson. G. G., 1944, Tempo and Mode In Evolution, Columbia University Press, New York, p. 158.