Explain why individuals cannot evolve?

Answer 1

Individuals die. Only the progeny of individuals carry on the genetic variation that is in populations. Selection works on this variation in populations by working on variation passed along by the sex cells. Somatic cells of the individual can have any mutation, but can not pass it on to progeny. Sex cell, having mutation which allow selection to choose among variation, lead to evolutionary processes.

Answer 2

An individual can evolve in a way - in their thinking or way of looking at life. The other kind of evolution in a physical sense, takes many generations for even a tiny change to happen.

Added:

Because individual die and all changes to their somatic genomes die with them. Only mutations, or regular recombination events, in the germ line can be passed on to progeny which can then change the allele frequency in the populations gene pool.

Evolution is the change in allele frequency over time in a population of organisms.