Creationists long ago gave up on their original idea of fixity of species. One reason is because simple calculation can show that Noah's Ark could not possibly have held pairs from each of some two to five million species (there would be less than one-half cubic foot per pair), nor could Noah and his family have possibly taken care of them all. A second reason is that the evidence for adaptive change and species formation is overwhelming. Therefore, they had to develop another concept.
Original Created Kinds
The current creation science stand on this matter is very nicely summed up by Dennis Wagner, editor of Students for Origins Research, in his answer to a letter by Dr. C. A. Zimmerman of Aurora College. Zimmerman asked whether or not creationists are "opposed to any and all evolution for any and all cases." Wagner defined three levels of evolution and stated that creationists object only to the third level-macroevolution-which leads to the formation of higher taxonomic categories such as genus, family, order, and so forth. He then said:
The main thrust of the creationist belief is that there is a set of originally created kinds that were designed with a vast but limited potentiality for variation. This variation was gradually released through the degenerative process of inbreeding in which the offspring species never again reach the hereditary variability of the parent.
He proposed that the term genus should apply to the original created kind and finished with:
Is the creationist opposed to macroevolution then? Well according to the definition of macroevolution, sometimes yes, sometimes no. If by macroevolution it is meant descent with modification of the coyote, wolf,
dingo, pampa fox, asiatic jackal, and domestic dog from the originally created Canid kind, then the answer is no, the creationist is not opposed to macroevolution. If, however, the definition of macroevolution means the descent with modification of the bird kind from the reptilian kind, then the answer is yes, the creationist is opposed to macroevolution.
Creationists do not have an exact definition of the original created kind for the same reasons that taxonomists cannot precisely define species: every imaginable gradation between species exists. Gish, a leading creation scientist, says that a basic animal or plant kind would include all species that have truly shared a common gene pool (1978). Furthermore, although no new kinds have arisen since the original creation, "the concept of special creation does not exclude the origin of varieties and species from an original created kind" (p. 40). In an article that first appeared in Creation Research Society Quarterly in 1971, F. L. Marsh says:
The descriptions of kinds in Genesis I give us ground for hypothesizing that the individuals of any particular Genesis kind would have chemistries sufficiently alike to make them fertile inter se, but sufficiently different to make them incompatible with individuals of every other kind. If this hypothesis is valid, then ability to cross would demonstrate membership in the same basic type.
He then lists examples of plant and animal kinds, based upon "true fertilization." that is, whether or not "both reduced parental sets of chromosomes join and participate in the first division of the fertilized egg." In cases such as horses and asses, or dogs, coyotes, and wolves, the genus is the kind (or the baramin, as creationists call it). If members of different families within an order can be crossed, that order is the created kind, and so on. He admits that in some cases mutation and chromosomal rearrangements may have occurred that prevent interbreeding, but membership in a kind can be determined from external appearance as in fruit flies.As biologists have recognized for over half a century, this is an objective and testable approach to the question of origins. An enormous amount of experimental hybridization has been done and is being done to help taxonomists assess relatedness in classifying many plant and animal species. Evolutionists interpret the results as strongly supporting the theory of descent with modification. Although creationists also appear to agree, within the limits stated by Wagner (1980) and Marsh (1971), they reject or ignore a large body of straightforward evidence that relates directly to the question of common descent and hybridization. Evidence is accepted by creationists only when it does not conflict with their beliefs.
Determining Genetic Relationship
An overwhelming body of experimental evidence clearly shows that the ability to
form hybrids is strongly tied to the amount of genetic relatedness between species. Genetic relatedness can be directly measured by a number of techniques (Dobzhansky, et al., 1977). Members of a local population exchange genes freely and are genetically very similar. On a scale of zero to one, their "genetic similarity" (one measure of the proportion of shared genes coding for essentially identical proteins) is 0.90 or higher. Some barriers to hybridization may exist between subspecies whose genetic similarity is about 0.8. Full species have genetic similarities ranging from 0.8 to about 0.3 and usually have substantial, if not complete, barriers to hybridization, and so on (Ayala, 1975).
Numerous studies show that chromosomal similarity is also a good measure of genetic relatedness. The fine structure of the gene-bearing chromosomes is an extremely complex pattern of bands and lines. The probability that two different chromosomes would independently arrive at identical banding patterns is essentially zero. Wallace details the evidence that identical chromosomes in two different species prove common ancestry just as surely as identical scratch patterns on two bullets prove both came from the same gun (1966). Even so, related species do not always have highly similar chromosome numbers or banding patterns because extensive chromosome rearrangements sometimes occur during speciation (White, 1978). Chromosome differences, when great enough, can cause the hybrids to be sterile, as in mules (Kaminsky, 1979), or to die as embryos. as in the cross between the domestic dog and the red fox (Chiarelli, 1975). If the differences are too great, the sperm will not even penetrate the egg. Conversely. the more similar the chromosomes of a sperm and an egg, the more likely their combination will result in Marsh's "true fertilization."
Evolutionists and creationists alike realize that all living species of a "kind" have inherited their genes from the same original ancestral species. Therefore, their body forms, chemistry, physiology, chromosomes, and genes are very similar. Conversely, the more similar any pair of species is for any and all of these features, the more likely it is they are descended from a close common ancestor and the more likely it is they can hybridize. If two species appear similar and are known to share most of their genes, creationists are usually perfectly willing to accept them as one "kind." If they are all interfertile, they are certainly one "kind." For example, asses, horses, zebras, and onagers all look rather similar. Their habits, behavior, diets, digestive systems, the proteins in their bodies, and the genes that manufacture those proteins are also similar. Moreover, the species in these four groups differ almost equally from other animals, such as rhinos. They form an obvious "natural group": the family Equidae. The final proof of their close relationship is that all are more or less interfertile, in spite of some differences in chromosome numbers (Ryder, et al., 1978).
The general rule is that the higher the genetic similarity and/or the more similar the chromosomes of two species are in number and structure, the higher the probability that they can hybridize (Dobzhansky, et al., 1977; Gray, 1971).
Thus, even in cases where hybridization experiments have not yet been conducted, the likelihood of successful hybridization can be objectively predicted.These objective criteria, for example, can be used to determine the relatedness of two ape species-the gibbon and the siamang-and, thus, how likely they are to be one "kind." They are easily distinguished, and taxonomists have placed them in different genera of the same family. These two species live together in Southeast Asia, but are not known to interact. The gibbon has twentytwo pairs of chromosomes, the siamang has twenty-five pairs. Their chromosome banding patterns have been so extensively rearranged that only one chromosome still bears a recognizably similar banding pattern in both species (Myers and Shafer, 1979).-Their genetic identity, another measure of the proportion of their genes coding for essentially identical proteins, is 0.76 (Bruce and Ayala, 1979). No natural hybrids have ever been reported. Their separation into different genera seems morphologically and behaviorally justified. However, they are genetically as closely related as most rodent species belonging to one genus (Ayala, 1975). They appear, chromosomely, to be at least as closely related as horses (thirty-two chromosome pairs) and onagers (twenty-seven to twenty-eight pairs) (Ryder, et al., 1978) or domestic dogs (thirty-nine chromosome pairs) and the red fox (eighteen to twenty pairs) (Chiarelli, 1975): Scientists view these observations as strong evidence for close evolutionary relationship. Since 1975, two hybrids have been born in the Atlanta, Georgia, Zoo (Myers and Shafer, 1979). Gibbons and siamangs unquestionably are highly modified descendants of a recent common ancestor, according to both evolutionist and creationist criteria.
Let us now apply these principles to another pair of mammal species. Their genetic identity is 0.70, about equal to the gibbon and siamang. Unlike the gibbon and siamang, their chromosomes are virtually identical even though one species has one pair of chromosomes more than the other. It is remarkable that 99 percent of the chromosome banding sequences of one species are clearly discernible in the chromosomes of the other species. The banding sequences are mostly in the same locations in the two chromosome sets, but in one species nine short segments are inverted, eighteen chromosomes have other minor changes, and one long chromosome has split to form two short ones, accounting for the different number of chromosomes. No hybrids have been found in nature, and no one has reported producing them in the laboratory. Nevertheless, if the proven criteria for genetic relatedness are objectively applied, these two species are merely one more example of close common descent or "variation within a created kind."
Few—whether evolutionist or creationist—would object to this interpretation if the species in question were fruit flies, horses, dogs, or even- monkeys; but the two species involved are actually humans and chimpanzees (Bruce and Ayala, 1979; Miller, 1977; King and Wilson, 1975; Yunis, et al., 1970). Evolutionists are not surprised, because these observations simply agree with previous fossil, anatomical, and embryological evidence. The picture suddenly changes for scientific
creationists, however, because they are irrevocably committed to the tenet that humans are unique. All members of the Institute for Creation Research (ICR) must sign a statement of faith affirming their belief that humans were separately and specially created. The statement that humans did not evolve from an animal ancestor is ICR tenet number 4 and is incorporated in the ICR bylaws (Morris, 1980). This belief forces them to deny that all this evidence, which would be compelling proof of close relationship for almost any other species pair, has any relevance at all. A typical creationist reply might be that, at most, they show a common designer.
A Double Standard
The important question here is whether or not changing the meaning of evidence in cases where it conflicts with a belief is scientifically legitimate or intellectually honest. Accepting that a body of evidence infers common ancestry for flies, horses, cats, or dogs, but claiming that exactly analogous evidence infers nothing about human-ape ancestry is not sound scientific reasoning. It is blind prejudice. Creationists clearly reject evolution in this case not because there is scientific evidence against it but because it conflicts with a cherished belief.
When creationists finally acquiesced to the voluminous evidence that species had not remained absolutely fixed and unchanged since creation, they lost their war against the concept of evolution. Because the direct evidence for species divergence (that is, speciation) is so abundant and straightforward, "scientific" creationists had to accept it or appear as irrational as those who use the Bible to argue that the earth is flat. Creationists now argue that new species may arise within kinds, but that no species may change into a new kind. The question is: what limits divergence? Sheep and goats can hybridize. If one "kind" can diverge this far, why not as far as sheep and cattle or sheep and camels? If that far, why not further? Gene products and the genes themselves show no boundaries between kinds. All available evidence suggests that, as long as they reproduce, as long as their genes mutate, and as long as they are subjected to selection, species will continue to diverge, essentially without limit.
I suggest that creationists made a tactical error when they began to pay attention, albeit selectively, to scientific evidence. This is because that evidence actually contradicts their most sacred belief: the belief that humans are uniquely created. Even if "true fertilization" between human and ape were reported, would scientific creationists reject special creation and accept the evolutionary relationship of humans and apes? If they were rational practitioners of science they would.