What`s an example of microevolution?

Microevolution is defined as a change in gene frequency in a population. Because of the short timescale of this sort of evolutionary change, we can often directly observe it happening. We have observed numerous cases of natural selection in the wild, as exemplified by the three shown here.

The Size of the Sparrow

House sparrows were introduced to North America in 1852. Since that time the sparrows have evolved different characteristics in different locations. Sparrow populations in the north are larger-bodied than sparrow populations in the south. This divergence in populations is probably at least partly a result of natural selection: larger-bodied birds can often survive lower temperatures than smaller-bodied birds can. Colder weather in the north may select for larger-bodied birds.

The persistence of lactase, the enzyme which digests milk sugar, into adulthood in white people. They live in areas where sunlight is weak, making it hard for the skin to synthesise vitamin D, although it has become fair to help that too. Therefore, they eat dairy. If they couldn't digest dairy as adults, it would be harder for them to get hold of dietary vitamin D. It's microevolution because it hasn't involved us becoming a different species or taxon - we can still interbreed with other races who can't digest dairy as adults.