A ---(1)--- is a group of individuals of the same species that mate and produce offspring. In each generation, new genotypes occur that express themselves as specific individual ---(2)---. Any factor that affects the ---(3)--- of a population can change the frequency of ---(4)---, resulting in evolution over time. Through the processes of variation and ---(5)---, new species can arise. A ---(6)--- is a population of physically similar, interbreeding organisms that do not interbreed with other such groups.