which theory says that populations change slowly over time?
Evolution is a scientific theory used by biologists. It explains how living things change over a long time, and how they have come to be the way they are. Earth is very old. By studying the layers of rock that make up Earth's crust, we can find out about its past. This kind of research is called historical geology.
Population Evolution Smallest Unit of Evolution One misconception is that organisms evolve during their lifetimes. Natural selection acts on individuals, but only populations evolve. Consider, for example, a population of medium ground finches on Daphne Major Island; Microevolution is a change in allele frequencies in a population over generations.