Lamarck vs Darwin

According to Lamarck, evolution occurs because organisms can inherit traits which have been acquired by their ancestors. For example, giraffes find themselves in a changing environment in which they can only survive by eating leaves high up on trees. So, they stretch their necks to reach the leaves and this stretching and the desire to stretch gets passed on to later generations. As a result, a species of animal which originally had short necks evolved into a species with long necks.

Natural selection explains the long necks of the giraffes as a result of the workings of nature which allowed the species to feed off of the leaves which grow high on trees rather than graze as short-legged, short necked animals are prone to do. There was no purposive behavior which was a response to the environment which was then passed on to later generations. There was simply an environment which included trees with leaves up high and that was a favorable food source to long-legged, long-necked animals such as the giraffe. In fact, according to natural selection, if that were the only food source available, only animals with long- necks, or animals which can climb or fly, would survive. All others would become extinct. There is no plan here, divine or otherwise, according to natural selection. Furthermore, there is nothing special signified by the fact that a species has survived. Survival of the fittest means only that those who have survived were fit to survive. It doesn't mean that those who survive are superior to those species which don't. They've survived because they were fit to adapt to their environment, e.g., they had long necks when there was a good supply of food readily available high up in the trees and there were no other catastrophic disadvantages to their height. For example, if a species got so tall that it became impossible to mate, it would become extinct. Or, if the only food source on high happened to have a substance in it which rendered giraffes sterile, there would be no more giraffes, no matter how hard they tried to will themselves potent.