Which is a requirement for natural selection to occur? heritable variations for some traits the ability of an organism to improve a trait during its lifetime equal probability of survival for all offspring fewer offspring than the environment can support

The answer would be A. Heritable variations for some traits

Variation in traits and characteristics is what drives natural selection. Organisms are naturally selected because of their phenotypes(physical characteristics) and some that have more suitable phenotypes are favored(they get to live longer and reproduce). If these variations didn’t exist no one would be favored and there’d be no natural selection or evolution basically:)

An example would be different fur colors for wolves that live in a mountain/polar ecosystem. One has white fur one has gray fur for example. The one with white fur would of course be naturally selected by the environment.

Hope this helps clear up this concept:)

Homologous chromosomes with heterozygous alleles d) heterozygous chromosomes with homozygous alleles