310 I The Process of Evolution 



percepts that people easily agree on: the height of a column of mer- 

 cury, the number of rats in a litter, the length of a femur, etc. Per- 

 haps the best description of this idea of descent with modification is 

 that it is a theory that seems to be overwhelmingly supported by the 

 available evidence. To a lesser degree, the same statement can be 

 made for the broad outlines of the evolutionary process as cur- 

 rently understood. 



The strong urge to believe in present evolutionary theory, which 

 is so evident among workers in the field, seems to stem partly from 

 a very common human error, the idea that one of a number of cur- 

 rent explanations must be correct. One usually finds the theory of 

 evolution being contrasted with that of special creation, a one-sided 

 contest, to say the least. The demonstration that the idea of special 

 creation is scientifically meaningless does not, however, "prove" 

 that the theory of evolution is correct. Current faith in the theory 

 is reminiscent of many other ideas which at one time were thought 

 to be self-evidently true and supported by all available data— the 

 flat earth, the geocentric universe, the sum of the angles of a triangle 

 equaling 180 degrees. It is conceivable, even likely, that what might 

 facetiously be called a non-Euclidean theory of evolution will be 

 developed. Perpetuation of today's theory as dogma will not en- 

 courage progress toward more satisfactory explanations of observed 

 phenomena. As Hardin puts it: "There is always a considerable lag 

 in teaching. Many years ago it was remarked that the Military 

 Academy of St. Cyr in France trained its students splendidly to fight 

 the battles of the last war. So it is in science teaching; we too often 

 train our students to fight battles already won, or equip them with 

 weapons that no longer fire." 



Is our current explanation of evolutionary processes without flaws? 

 Hardly; even the most sanguine evolutionist would admit that there 

 is much to learn. The fine theoretical structure of population genetics 

 has not been thoroughly tested in natural populations. Indeed, it is 

 only recently that biologists have begun to realize that very large 

 selection coefficients may be the rule rather than the exception in 

 nature. ( One of the triumphs of theoretical population genetics was 

 to show that, in view of the long periods of time available, very small 

 selection coefficients could account for the observed diversity of 

 fife. ) Although the broad outlines of the splitting processes in evolu- 

 tion seem to be understood adequately, no general mathematical 

 treatment has been possible, and many of the details are obscure. 



For instance, the kinds of interactions that lead to patterns of dif- 

 ferentiation such as are shown by the Galapagos finches (Chap. 10) 

 have not been satisfactorily analyzed. To say that "competition be- 



