The genetic makeup of a population changes over time. This change happens through the processes of:

* Mutation: Random changes in DNA sequences introduce new genetic variations.

* Natural Selection: Individuals with traits that make them better suited to their environment are more likely to survive and reproduce, passing on those advantageous traits.

* Genetic Drift: Random fluctuations in allele frequencies, particularly in small populations.

* Gene Flow: The movement of genes between populations, which can introduce new variations or alter existing ones.

This continuous evolution leads to:

* Adaptation: Populations becoming better suited to their environment over time.

* Speciation: The formation of new species through the accumulation of genetic differences.

* Diversity: The wide variety of life on Earth, resulting from millions of years of evolution.

It's important to understand that evolution is a gradual process. It doesn't happen overnight, and it doesn't always mean that a population becomes "better" or "more complex." It simply means that the genetic composition of a population is constantly changing in response to its environment.