The Future Of Human Evolution Essay Research — страница 3
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small number of offspring, then even in the absence of all selective forces, the frequency of a gene will not be exactly reproduced in the next generation because of sampling error. If in a population of 1000 individuals the frequency of “a” is 0.5 in one generation, then it may by chance be 0.493 or 0.0505 in the next generation because of the chance production of a few more or less progeny of each genotype. In the second generation, there is another sampling error based on the new gene frequency, so the frequency of “a” may go from 0.0505 to 0.501 or back to 0.498. This process of random fluctuation continues generation after generation, with no force pushing the frequency back to its initial state because the population has no “genetic memory” of its state many generations ago. Each generation is an independent event. The final result of this random change in allele frequency is that the population eventually drifts to p=1 or p=0. After this point, no further change is possible; the population has become homozygous. A different population, isolat ed from the first, also undergoes this random genetic drift, but it may become homozygous for allele “A”, whereas the first population has become homozygous for allele “a”. As time goes on, isolated populations diverge from each other, each losing heterozygosity. The variation originally present within populations now appears as variation between populations (Suzuki 704). The evolution of man can be broken up into three basic stages. The first, lasting millions of years, slowly shaped human nature from Homo erectus to Home sapiens. Natural selection provided the means for countless random mutations resulting in the appearance of such human characteristics as hands and feet. The second stage, after the full development of the human body and mind, saw humans moving from wild foragers to an agriculture based society. Natural selection received a helping hand as man took advantage of random mutations in nature and bred more productive species of plants and animals. The most bountiful wheats were collected and re-planted, and the fastest horses were bred with equally faster horses. Even in our recent history the strongest black male slaves were mated with the hardest working female slaves.