Following his return to England, Darwin did, indeed, study plant and animal breeding, because he saw in it the same processes of variation and development he had witnessed in his analysis of species on his travels. Yet, those variations had arisen without such conscious intervention, and Darwin sought, in his study, of plant and animal breeding to identify what those processes were, and how Nature might itself have brought them about.
The process has two components – variation and heredity. We now know, as a result of the science of genetics, that the characteristics of all organisms are determined by their genes, and these genes are inherited from their parents. Large numbers of new organisms come into existence and they all differ one from another, because they all have a different sequencing of their genes, as we now further understand as a result of the decoding of these genomes, which computer technology made possible, 20 years ago.
As a result of these minor differences in the genes, of any given species, they will have different characteristics. Depending upon the material conditions, in which the given species exists, some characteristics will be more beneficial than others. A plant whose characteristics mean that it tends to be even slightly taller than others may poke its head higher, obtain more sunlight and grow stronger. It will be more likely to survive, and so will pass on its characteristics to the plants that grow from its seed. The plant, of course, did not consciously grow taller to achieve that advantage, it was simply better adapted to those conditions. In other conditions it might have been a disadvantage.
“However great Darwin's blunder in accepting the Malthusian theory so naively and uncritically, anyone can see at the first glance that no Malthusian spectacles are required to perceive the struggle for existence in nature — the contradiction between the countless host of embryonic germs nature so lavishly produces and the small number of those which can ever reach maturity, a contradiction which in fact finds its solution for the most part in a struggle for existence — often of extreme cruelty.” (p 86)
Yet, Duhring could not see any possibility of a struggle for existence amongst unconscious plants or plant eaters, restricting it only to “the brutes”, and, having done so, then, moralistically, rails at the brutality of this process. He accuses Darwin of producing “its transformations and differences out of nothing” (p 87) But, this is not true, as set out above. The transformations occur as a result of the inheritance of advantageous characteristics.
“It is true that, when considering natural selection, Darwin leaves out of account the causes which have produced the variations in separate individuals, and deals in the first place with the way in which such individual deviations gradually become the characteristics of a race, variety or species. To Darwin it was of less immediate importance to discover these causes — which up to the present are in part completely unknown, and in part can only be stated in quite general terms — than to find a rational form in which their effects become fixed, acquire permanent significance.” (p 87-8)
But, we do know, now, the causes of these variations, which reside in the genetic make-up of the different individuals of a given species. We also know that other causes play a part, such as arising from mutation, as well as, more recently, becoming aware of the role of epigenetics in the way that certain genes within the genome of an individual may be turned on or off.
“It is true that in doing this Darwin attributed to his discovery too wide a field of action, made it the sole agent in the alteration of species and neglected the causes of the repeated individual variations, for the form in which these variations become general; but this is the kind of mistake which he shares with most other people who make any real advance.” (p 88)
This is quite correct, as not only does mutation play a role, but, also, there is the role of mass extinctions, which, for example, wiped out the dinosaurs, except for the birds, and which suddenly created conditions where other species may prosper.
No comments:
Post a Comment