* Individuals do not evolve. Evolution is a change in the genetic makeup of a population over generations. While an individual might experience changes during their lifetime, these changes are not passed down to their offspring, and therefore, do not contribute to evolution.

* Species are a broader category than populations. While species evolve, the process happens through changes in the genetic makeup of the populations that make up the species.

* Populations are groups of individuals of the same species living in a particular area. They are the unit of evolution because:

* Genetic variation: Populations have genetic variation, meaning there are differences in the genes of individuals within the population.

* Natural selection: Natural selection acts on this variation, favoring traits that increase survival and reproduction.

* Inheritance: Individuals with favorable traits pass those traits down to their offspring. Over time, this leads to changes in the overall genetic makeup of the population, which is the definition of evolution.

In summary: Evolution is a change in the genetic makeup of a population over time. Individuals do not evolve, but the changes in the population's genetic makeup are what drives the evolution of species.