Darwin Revisited

December 3, 2009 | Leave a Comment

Category: Biology

Exploring some of the original sources of the ideas I play with in this blog, I’m revisiting Darwin’s The Variation of Animals and Plants under Domestication.  In this two-volume presentation of Darwin’s Lamarckian hypothesis, published in 1868, after his 1859 On the Origin of Species, Darwin does not associate himself with Lamarck.  Lamarck is rarely mentioned.  Then, as now, evolutionary theories focusing on use and disuse of organs and environmental effects were controversial.  Some sample excerpts….

“…selection does nothing without variability, and this depends in some manner on the action of the surrounding circumstances on the organism.”  V1, p. 7

Describing the transformation of several English dog breeds when raised in India, Darwin states, “It would appear that climate to a certain extent directly modifies the forms of dogs.  We have lately seen that several of our English breeds cannot live in India, and it is positively asserted that when bred there for a few generations they degenerate not only in their mental faculties, but in form….This remarkable tendency to rapid deterioration in European dogs subjected to the climate of India and Africa, may be largely accounted for by reversion to a primordial condition which many animals exhibit, as we shall hereafter see, when their constitutions are in any way disturbed.”  V1 pp. 39-40

Regarding dogs, “We may, however, readily admit that abundant and rich food supplied during many generations would give an inherited tendency to increased size of body, and that from disuse, the limbs would become finer and shorter.”  V1 p. 76

Particularly relevant to the hypothesis promoted in this blog is Darwin’s assertion that both selective process, in this case human selection of specific pigeon features, and environmental effects combine to compel species change.  “Each slight change in the length or shortness of the beak, in the length of leg, &c., has no doubt been indirectly and remotely caused by some change in the conditions to which the bird has been subjected, but we must attribute the final result, as is manifest in those cases of which we have any historical record, to the continued selection and accumulation of many slight successive variations.”  V1 p. 225

Darwin was a pluralist.  He believed that several selective processes working together effect change.  He said this of chickens, “Thus from occasional appearance of abnormal characters, though at first only slight in degree; from the effects of use and disuse of parts; possibly from the direct effects of changed climate and food; from correlation of growth; from occasional reversions to old and long-lost characters; from the crossing of breeds, when more than one had been formed; but, above all, from unconscious selection carried on during many generations, there is no insuperable difficulty, to the best of my judgment, in believing that all [chicken] breeds have descended from some one parent source.”  V1 p. 245

“…the act of crossing often leads to the reappearance or reversion of long-lost characters; and in most cases it would be impossible to distinguish between the reappearance of ancient characters and the first appearance of absolutely new characters.  Practically, whether new or old, they would be new to the breed in which they appeared.”  V2 p. 252

Did Darwin ever consider that humans having difficulty speaking might be evidencing the reappearance of long-lost characters?

“The causes which induce variability act on the mature organism, on the embryo, and, probably, on the sexual elements before impregnation has been effected.”  V2 p. 259

Darwin was a radical evolutionary developmental biologist offering ideas not even in evidence today.

There were principles that Darwin embraced that were not included in the synthesis of the 1930s and 1940s.  The importance of early development and embryo studies to an understanding of the power of the environment to inform structure and behavior has only recently begun an integration into established orthodoxy with the recognition of evo devo.  Darwin placed a heavy emphasis in his post-Origin works on the influence of the environment on variation.  As noted by Gould, this has been perhaps the longest, most controversial issue wrestled with by biologists for 150 years.  For Neo-Darwinians, it seems to have philosophical, even religious, ramifications.

It has been the case for over a century that evolutionary theorists pull excerpts from Darwin that support their particular point of view, ignoring what Darwin said that goes in other directions.  Darwin’s complete works reveal a vast collection of examples of evolution impacted by a variety of selective processes.  Contemporary theorists would do well to read all three of this great man’s great works.


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