Chapter The Spectre of Lamarck of The Origin of Species - Study Guide by Charles Darwin

The Spectre of Lamarck

Unfortunately, the preponderance of sex in the natural world presented Darwin with not only a boost to his theories, but also a problem: whilst sex increases the levels of variation over the generations, and hence the level of raw material for selection, it also presented the question of how that variation is maintained. Before the discoveries of Gregor Mendel (see 'Missing Links') became widely known and understood, it was widely believed that an organism produced by sexual reproduction received a 'blend' of its characteristics from its parents. However, such a blending inheritance would have the effect of ironing out the discrete traits that are the handles for natural selection to grasp hold of: a favourable variation would soon disperse itself as the favoured individual interbred with 'normal' members of the population. That this didn't appear to be the case proved no little headache for Darwin and evolutionary theory in general, until the reconciliation of Mendelian genetics with Darwinian Natural Selection. In fact, combined with an erroneous estimation of the age of the earth by the physicist Lord William Kelvin (1824-1907) that was insufficiently great to allow the pace of evolutionary change that natural selection requires, the blending objection undermined Darwin's faith in his initial theories. So much so that he found himself arguing himself back into the corner of Lamarkianism. He had already left room for some change through use and misuse in the First edition of Origin, but by the Sixth he concluded that natural selection is "aided in an important manner by the inherited effects of the use and disuse of parts; and in an unimportant manner, that is in relation to adaptive structures, whether past or present, by the direct action of external conditions… It appears that I formerly underrated the frequency and value of these latter forms of variation, as leading to permanent modifications of structure independently of natural selection." He even went as far as proposing a mechanism through which Lamarckian evolution could proceed. This theory, which Darwin called Pangenesis, had its roots in the ideas of the Ancient Greek philosopher Democritus (c.460 - c.370 B.C.), described by Juvenal as a man perpetually amused by the follies of man. Darwin hypothesised that the germ cells (sperm and eggs) of an individual gradually accumulated a set of representative particles, or 'gemmules', derived from all the organs and tissues of the body. Therefore characteristics acquired before reproduction had a route through which they could be transferred to the next generation. Though it is unfortunate that Darwin succumbed to his critics in his own lifetime, and Lamarckianism remains one of the most consistent misunderstandings of how evolution operates, Darwin's original ideas have been largely vindicated by posterity.