How does Charles Darwin's idea of natural selection work?
Individuals within a species show variation because of the differences in their genes. Some individuals are better adapted to their environment than others and these individuals will be more likely to survive and reproduce, passing on their characteristics to the next generation. Over generations, the useful characteristics (that lead to a better chance of survival) will become more common in the population. (N.B individuals in a species are naturally selected for but individuals cannot evolve - only a species as a whole can evolve)