Darwin's Gradualism

Abstract

We protest the inaccurate accusation made against us by Penny (1983) in his recent comment on Darwin, gradualism and punctuated equilibrium. He cited a quotation from Darwin as we rendered it (Eldredge and Gould, 1972:87), saying that we apparently took it from the first edition of the Origin, then claiming: However, not a verbatim extract. As evidence, he reproduced a passage from the sixth edition of the Origin, in which the words cited by us are interspersed amidst a variety of other sentences that supposedly alter their meaning. Contrary to Penny's charge, the quotation as given by us an accurate verbatim extract from the first edition of the Origin (1859:342), except that the words is and this fact, which we interpolated, should have been given in brackefs, but were not (by typographical error) in our original paper (1972:87). Penny argued that, because Darwin acknowledged in several places the potentially highly variable character of evolutionary rates, he was not a committed gradualist and, if not actually the father of punctuated equilibrium, he at least veered sufficiently close to it to deprive us of any marked originality. One simply cannot do history by searching for footnotes and incidental statements, particularly in later editions that compromise original statements. As with the Bible, most anything can be found somewhere in Darwin. General tenor, not occasional commentary, must be the criterion for judging a scientist's basic conceptions. Darwin historians agree on a single point (for example, see Gruber [1974] and Mayr [1982]), it the importance and pervasiveness of Darwin's gradualism-a commitment far stronger than his allegiance to natural selection as an evolutionary mechanism. After a brief and early flirtation with saltation in his 1837 notebooks, Darwin never wavered in his support of gradualism (of course, with the possibility of marked variation in rate). He wrote in the section on geology from the 1842 sketch of the Origin (Darwin, 1909: 23): Our theory requires a very gradual introduction of new forms, and extermination of the old .... The extermination of old may sometimes be rapid, but never the introduction. In the groups descended from common parent, our theory requires a perfect gradation not differing more than breeds of cattle, or potatoes, or cabbages in forms. This commitment to gradualism underlies the most striking imaginery of the Origin itself, particularly the famous passage (Darwin, 1859:84): It may be said that natural selection daily and hourly scrutinising, throughout the world, every variation even the slightest; rejecting that which bad, preserving and adding up all that good; silently and insensibly working .... We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages. Most striking Darwin's continual conflation of gradualism with natural selection, the very point that inspired Huxley's major criticism: You load yourself with an unnecessary difficulty in adopting Natura non facit saltum so unreservedly. Darwin (1859:189) wrote, for example, making his usual conflation: If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. To deny Darwin's strict