[Kabal]

(08-14-2013 10:13 PM)Caveman Wrote:  

During the evolution of a species the number of chromosomes also changes due to some random mutation.

But these beneficial random mutations that change the species for the better happen very rarely, and for every one mutation that brings positive character traits there are like a million mutations that bring negative ones.

This is a good rule of thumb.

Evolution finds local optimums, both in a mathematical and geographical sense.

Thus, any random deviances (mutations) will be much more likely to be deleterious than beneficial.

However, random positive mutations can indeed sweep through a human population very quickly.

Much more quickly than laymen, even ones cursorily familiar with evolutionary concepts, might realize.

In The 10,000 Year Explosion, Cochran and Harpending note that a 7% initial selective advantage could result in most of a population having that trait after 6,000 years (page 135), in reflecting upon the ApoA-IM mutation, which went from 1 copy to 43 in ten generations in Italy.