Barb,
I am glad you mentioned Gould's book. It jogged my memory so I got it down from my bookshelf and found this interesting passage that has recently been confirmed by evo-devo research. Some here have criticized my viewpoint that there needed to be only a relatively few animals on the Ark in order to repopulate the world so rapidly with the vast variety we see today. The article hints at how this could be, although Gould obviously still held the "long ages" concept. Once again, evolutionists (and cosmologists) have come close, but no cigar, probably because they refuse to give God the glory.
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180 HEN’S TEETH AND HORSE’S TOES
O. C. Marsh, a founder of vertebrate paleontology in America, took a special interest in these aberrant animals and published a long article on “Recent polydactyle horses” in April 1892. Marsh had two major claims upon fame, one dubious – his acrimonious battles with E. D. Cope in collecting and describing vertebrate fossils from the American West – and one unambiguous – his success in deciphering the evolution of horses, the first adequate demonstration of descent provided by the fossil record of vertebrates, and an important support in Darwin’s early battles.
Marsh was puzzled and fascinated by these aberrant horses with extra toes. In most cases, the additional toe is merely a duplicate copy of the functional third digit. But Marsh found that many two- and three-toed horses had harkened back to their ancestors by developing either or both of the side splints into functional (or nearly functional) hoofed toes. (A later, and particularly thorough, German monograph of 1918 concluded that about two-thirds of horses with extra toes had simply duplicated the functional third digit, while about one-third had resuscitated an ancestral feature by developing the vestigial splints of their second or fourth toe into complete, hoofed digits.) These apparent reversions to previous evolutionary states are called atavisms, after the Latin atavus: literally, greatgreat-great-grandfather more generally, simply ancestor. The biological literature is studded with examples of the genre, but they have generally been treated anecdotally as mere curiosities bearing no important evolutionary message. If anything, they are surrounded with the odor of slight embarrassment, as if the progressive process of evolution did not care to be reminded so palpably of its previous imperfections. The synonyms of European colleagues express this feeling directly—’ ‘throwback” in England, pas-enarnère (“backward step”) in France, and Rückschlag (“set-back”) in Germany. When granted any general significance, atavisms have been treated as marks of constraint, as indications that an organism’s past lurks just below its present surface and can hold back its future advance.
I would suggest an opposite view—that atavisms teach an important lesson about potential results of small genetic changes, and that they suggest an unconventional approach to the problem of major transitions in evolution. In the traditional view, major transitions are a summation of the small changes that adapt populations ever more finely to their local environments. Several evolutionists, myself included,
HEN’S TEETH AND HORSE’S TOES 181
have become dissatisfied with this vision of smooth extrapolation. Must one group always evolve from another through an insensibly graded series of intermediate forms? Must evolution proceed gene by gene, each tiny change producing a correspondingly small alteration of external appearance? The fossil record rarely records smooth transitions, and it is often difficult even to imagine a function for all hypothetical intermediates between ancestors and their highly modified descendants.
One promising solution to this dilemma recognizes that of certain kinds of small genetic changes may have major, discontinuous effects upon morphology. We can make no one-to-one translation between extent of genetic change and degree of alteration in external form. Genes are not attached to independent bits of the body, each responsible for building one small item. Genetic systems are arranged hierarchically; controllers and master switches often activate large blocks of genes. Small changes in the timing of action for these controllers often translate into major and discontinuous alterations of external form. Most dramatic are the so-called homeotic mutants discussed in the following essay.
The current challenge to traditional gradualistic accounts of evolutionary transitions will take root only if genetic systems contain extensive, hidden capacities for expressing small changes as large effects. Atavisms provide the most striking demonstration of this principle that I know. If genetic systems were beanbags of independent items, each responsible for building a single part of the body, then evolutionary change could only occur piece by piece. But genetic systems are integrated products of an organism’s history, and they retain extensive, latent capacities that can often be released by small changes. Horses have never lost the genetic information for producing side toes even though their ancestors settled on a single toe several million years ago. What else might their genetic system maintain, normally unexpressed, but able to serve, if activated, as a possible focus for major and rapid evolutionary change? Atavisms reflect the enormous, latent capacity of genetic systems, not primarily the constraints and limitations imposed by an organism’s past.
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Extrapolating even further backwards in time the problem must eventually be faced: HOW DID SUCH SOPHISTICATED CAPABILITIES FIRST ARISE?
Our God is great. :first:
