Science in Christian Perspective



Crossing In Relation to the Origin of New Groups*
Anderson College

From JASA 9 (December 1957): 5-7.

In this program we are considering the nature of change, as applied to groups of living things. Should we agree with the ancient Greek philosopher, Heraclitus, that all is in a state of flux, to the extent that we can count on nothing except change? Perhaps he, like some modern people, felt that the easiest. way to get a hearing is to shock people.

In the beginning, let us notice some principles upon which there is general agreement. The diversity which we see among living things is not to be accounted for as response to diverse environments. These so-called "acquired characters" last but a single generation and since they do not modify the germplasm they are not passed on to the next generation1. Many experiments have proved that the new generation starts, like its parents from the base line of the hereditary factors in its chromosomes.

There is general agreement, furthermore, that these hereditary factors or genes do not undergo gradual change.2 At each cell division they are carefully split into two equal genes, and the daughter genes are pulled by the spindle fibers into the newly formed cells. The only way in which a hereditary factor changes is by the reorganization called mutation, which will be discussed in detail, later.

I have been asked the question as to whether species can be crossed, and if the answer is in the affirmative, how much change this may effect. The question can not be given a simple and definite answer because there is not agreement as to what a species is. Certain criteria have been proposed but they are not applied alike by different classifiers.

A species is a group of plants or animals which is

*Paper presented at the Second Joint', A.S.A.-E.T.S. meeting at Wheaton, Illinois. June, 1957.

different from any other group and the individuals within the group resemble each other. But how much resemblance is required?  Some say they must be as much alike as litter mates, but other classifiers would say that this criterion exacts too much likeness and splits up the animals into too many species. If a classifier is a splitter he makes-a large nurnber of small species, while a lumper describes fewer species, but makes them larger.

Another criterion is that a species maintains its identity in nature. Thus a two-headed calf is not a member of a new species because , it is not the beginning of a new natural group. Now, in order for a species to keep its identity through, a series of generations, its members must mate only among, themselves. It is clear that if they mate with other species, the offspring will lose the distinctive morphology which justifies calling the group, a species.

This rule also has been applied diversly, however, for some groups have been split into different. species simply because they are found living in, different places. Linnaeus called the European buffalo Bos bonasus and the similar American animal Basbison, but when brought together they mated and Produced fertile offspring. Separated groups. of the ibex, genus Capra, likewise were assigned specific names, but were found to be cross fertile.3

A group smaller than a species, called a race, variety, or breed, mixes f reely with other groups and so loses its identity unless isolated by natural features such as islands or mountains or segregation by man. The crossing of these forms by such investigators as Mendel and Morgan has added many new :varieties of plants and, animals. The novelty consists of a new combination' of existing traits, rather than the creation of new traits.

In a few cases, even a new trait or character has been formed without a change in genes, but by bringing new genes together. For example a white rooster with black markings is mated with a black hen and the offspring are blue, called blue Andalusian chickens4.

It is readily seen, however, that these are not changes such as would bring about the postulated evolution of palms and pines, apes and peacocks from a blob of protoplasm. They are cyclic or alternative, not progressive, and in future generations the old characters reappear; for instance some chickens are splashed with white and some are black, along with the Andalusian blue.

A change which reorganizes a gene, or replaces it with a new one - - trades an old lamp for a new one, so to speak - - is called a mutation, and the animal or plant having this new gene is called a mutant. It is to be expected that a complex process such as reproduction would suffer an accident once in a while. If this accident results in a new character which is heritable we call it a mutation.

Let us look f irst at some of the mutants which are supposed to be good. The Ancon sheep had short legs and was kept because it could be easily fenced in, but later the breed was discontinued because it was painful for them to walk around and it seemed a pity to keep such animals. At the Connecticut Experiment Station a tobacco plant grew six feet tall with big leaves all the way up, but it forgot to go to seed5. We prize seedless grapes, seedless oranges, stringless green beans and hornless cattle, but it is hard to see how these mutations benefit the organisms which have suffered such a change. Typical human mutations include albinism, short fingers, and lack of tooth enamel.

H. J. Muller, who won the Nobel prize for his work in mutations, in Washington, 1946, was cornered by a group of newspaper men who asked him to discuss the outlook for improving the human race. He answered, "Most mutations are bad. In fact, good ones are so rare that we can consider them all as bad."6

Now it might be said that beneficial mutations are being overlooked, that it is not enough to say that we have not found them. But Austin Clark of the U. S. National Museum says they are naturally defective. "A subtraction of something. Those differing widely from normal cannot develop past the embryo."7 Dobzhansky also states that mutations which differ most from the normal are the most viable.8 Now if the biggest changes are the worst it must be that the whole lot is bad, and we are not simply overlooking the good ones. Julian Huxley also agrees;9 stating the larger the change the less likely it is to be an improvement.

Although a number of mutations have been seen to appear, we have not observed in them the advanced characters which would account for evolution. For instance, if evolution occurred it would be necessary that a mutation took place which changed a food vacuole to a stomach, one which substituted lungs for gills, another changing a nerve net into a brain. Still others would have to initiate a pancreas, an eye, and a mammary gland, even without percursor organs. Such changes have not been observed. In spite of the handicaps of changed form however, and the loss of vigor which usually accompany mutant organisms, some of them manage to survive. The large wingless bird, Apteryx australis and different species of wingless grasshoppers have the appearance of mutants. It may also be that the legs of snakes and the hind legs of whales were victims of this destructive type of change. The giant silk worms, Samia cecropia, whose pointed cocoons are marked here and there in trees by sharp eyes, seem to have lost their mouth parts by this process. But having stored much fat in the larval period, they are able to mate and lay their eggs before they die. In a changed environment a mutant character might even be an advantage, as an albino fox in the Arctic region. Thus the diversity of nature is increased.

This paper would not be complete without presenting the suggestion of a professor in a medical college in Los Angeles. The probability is that the original kinds were created with genes for characters which were latent and did not appear until later generations. Such a plant or animal, having diverse genes and more of them than can be expressed in one individual, is said to be heterozygous. This mixed condition is found in a plant or animal in a generation following a cross, and it is altogether possible that they were created mixed.

For instance, a heterozygous black, rough-coated guinea pig mated with another having the same characteristics will produce guinea pigs of that type and also three other types: namely white, rough-coated; white, smooth-coated; and black smooth-coated.

If such characters do not arise from latent original genes we would say that they arose from mutation. But it seems to me this explanation does not fit so well for they do not carry the reduced vigor f ound in mutants, nor lack of any normal part.

In answer to the question, "Do species cross" ?, it seems that some which have been so classified do cross. producing fertile offspring. Any such crossing tends to increase the diversity in animate nature, by making new combinations of genes.

New genes arise by mutation. but such as would account for advanced characters have not been ob served. Diversity may be accounted for by also postulating that the original plants and animals were created heterozygous.

1. R. W. Hegner and K. A. Stiles; College Zoology, 6th ed., P. 79; MacMillan.
2. L. H. Snyder; Prin. of Heredity, 3rd ed., p. 306; Heath.
3. R. Hesse, W. C. Allee and K. P. Schmidt; Ecological Animal Geography, p. 75.
4. Snyder, op. cit. p. 17.
5. E. B. Babcock and R. E. Clausen; Genetics in Relation to Agr., fig. 150; McGraw-Hill, 1918.
6. Time Magazine, Nov. 11, 1946, p. 96.
7. Austin Clark; New Evolution, Zoogenesis, p. 218; Williams and Wilkins, 1930.
8. T. Dobzhansky; Genetics and the Origin of Species, p. 53; Columbia Univ. Press, 1941.
9. J. Huxley; Evolution the Modern Synthesis, p. 115; Harper & Bros., 1942.