Explain the role of mutations, differential reproduction, and gene recombination in changing the gen

It is a common mis-perception that natural selection only works on inherited traits (genotypes). In actuality, natural selection only works on displayed traits (phenotypes). Stay with me, this is technical... (in fact, if this is for some school project, this answer is probably not what you want - alot of college students can't make this distinction).

It's true that for EVOLUTION to take place a change in the frequency of a genotype within a population must occur, which is why people often say natural selection acts on the genotype (or inherited traits). This is impossible; nature cannot percieve an organisms genotypes, only their phenotypes. Natural selection acts on the phenotype. It just so happens that statistically the phenotype has a high degree of correlation with the genotype, so though selection acts on the former, the latter is influenced as well.

Here's an example. Let's say a lion has the best possible genes in a population for speed, and strength. Typically, one would expect that lion to be selected for. What if this particular lion lives in an area that undergoes a severe drought? Or catches a virus that makes it ill? Although it still has the best genes, it will be weaker and slower than other lions, and thus natural selection will select against these strong genes. In the long run, however, strong genes will win out more often than weak genes, but as you can see natural selection acts on displayed traits, not inherited traits.

Oh, and of course displayed traits (phenotypes) aren't passed to the next generation, only the underlying genes (genotypes). So if a lion with weak genes works out alot and gets really buff, it's offspring will still have weak genes.

The incorrect belief that traits developed over an organism's lifetime can be passed to their offspring is Lamarckian evolution.

Any change to the organism that affects only the somatoplasm (does not affect the germ cells) cannnot be passed along to the offspring. It can, however, be selected against; it just won't make any difference in the next generation.

Would like to add that because inherited traits require reproduction to be passed on. Natural selection requires deaths in a population due to certain "weak" traits. Therefore, natural selection only acts on inherited traits as it prevents these traits from being passed on via reproduction through deaths in the population