Evolution at different scales: micro to macro :
What is microevolution?
Microevolution is simply a change in gene frequency within a population. Evolution at
this scale can be observed over short periods of time for example, between one
generation and the next, the frequency of a gene for pesticide resistance in a population
of crop pests increases. Such a change might come about because natural selection favored
the gene, because the population received new immigrants carrying the gene, because some
nonresistant genes mutated to the resistant version, or because of random genetic drift
from one generation to the next.