2011-05-24, 01:22 AM
Genetic variability in a population also comes from genes crossing over in meiosis and independent assortment of genes during meiosis. Combine that with possible, but rare, mutations and you can produce a number of different combinations. I think a single human pairing can produce 2^(23) x 2^(23) possible different combinations of gametes without mutations. Mutations can appear for a number of reasons, and Eos said the more common environmental ones. DNA may also be copied wrong (in gametes) and that mistake or mutation would be passed onto the offspring.
Evolution does not happen in an individual. Populations evolve. Over time, individuals who cannot survive are not as successful as individuals who have traits that let them survive and mate as a higher rate. Eventually these successful traits become prevalent in the population. It seems your confusion comes from a very limited knowledge on the subject; reading books about it or just reading articles online should clear up many of your questions, if you want to learn more.
Edit: You should read about the central dogma, too.
Evolution does not happen in an individual. Populations evolve. Over time, individuals who cannot survive are not as successful as individuals who have traits that let them survive and mate as a higher rate. Eventually these successful traits become prevalent in the population. It seems your confusion comes from a very limited knowledge on the subject; reading books about it or just reading articles online should clear up many of your questions, if you want to learn more.
Edit: You should read about the central dogma, too.