Evolution is the change of trait frequencies in a population. This change is the result of interactions between the abiotic, biotic and social environments, behaviors, bodies, brains, technologies, cultures, and genes of organisms. These interactions cause populations to change over time, as new features arise, some features become more common and others become more rare. These interactions therefore shape the evolution and development of our traits and our world.

Different scientists define and study evolution in different ways. Some are primarily interested in the change of genotypes and gene frequencies in a population. Others also look at change in many other things (phenotypes, e.g. behaviors, brains, bodies, social organisation, technologies, culture, and environmental features) in a population (see comparison table in Cultural Evolution). Depending on what we look at, there can be different ways that traits get inherited, transmitted or retained in a population – for example, through the inheritance of genes to offspring, or through imitation of behaviors. There can also be different ways how new variations of traits appear in the population, and different ways through which some traits become more common and others less common in a population.

If we want to understand the evolution of human behaviors and cultures, it makes sense to look at many different phenotypes and their interactions, and consider all of the possible mechanisms of their variation, selection, and inheritance.