Originally posted by rvsakhadeo
Many a times the defenders of Evolution use circular arguments. The essence of their defence is that this was the way the organism or its part has evolved automatically and this particular automatic stage of evolution has enabled the organism to survive/multiply better than its competitors lacking this particular stage of automatic evolution and hence th ...[text shortened]... shows that this bicameral division of brain which have specialised functions was an adaption.
Automatic evolution's been abandoned.
"Darwin knew that discontinuous variations or "sports" occurred, and that their effects were heritable, but he argued that such changes would not be important in evolution, which must occur gradually according to the doctrine of natura non facit salta (see gradualism). In Darwin's theory, infinitesimal hereditary variation arises automatically in response to the effect of "altered conditions of life" on "the sexual organs"; whenever conditions change, adaptation happens automatically (and by infinitesimal increments) as selection preserves fluctuations that fit the new conditions. That is, Darwin proposed a mechanism of automatic evolution, based on automatic variation that would always be present when needed.
However, genetics showed that the kind of variation that arises automatically in response to altered conditions is not genetic variation, but non-heritable environmental variation. Heritable variation, by contrast, arises spontaneously by events of "mutation". This is how the discovery of genetics forced a re-appraisal of the mechanism of evolution — a re-appraisal that led to the rise of "mutationism"."
"At the time of the Darwin centennial in Cambridge in 1909, Mutationism and Lamarckism were contrasted with Darwin's “Natural Selection” as competing ideas; 50 years later, at the University of Chicago centennial  of the publication of The Origin of Species, mutationism (like Lamarckism) was no longer seriously considered."