I see evolution as a mechanism whereby some aspect of individuals in the parent population is copied to individuals in the offspring population. Specifically I am interested in how skills are copied forward. I do not use evolution to refer to the historical record, since skills are in the brain and do not calcify or petrify to leave a historical record. We can make conjectures about the skilled behaviours of dinosaurs, we can make inferences about their skills, but we cannot run experiments on them in the lab or even observe them in the wild.
If one individual in the parent population copies to more individuals in the offspring population than another individual in the parent population, then the first individual is more successful, i.e. has greater fitness, than the second individual. Success depends on more than just skills, but having better skills helps, so skills contribute to fitness.
The first function, often called 'natural selection', is biased to reduce variance by selecting in favour of more successful skills, i.e. skill variants that make a more positive contribution to fitness. The result of the biased copying to the offspring population may result in a change of the characteristics of skills across the population. The change, when observed over several generations, may result in a drift, a bifurcation, or a multifurcation of the characteristics of the skill. A bifurcation of skill sets may be illustrated when nomadic hunter-gatheres either continued as nomads or became sedentary with agriculture. Multifurcation may be illustrated by the development of speech, resulting in many different languages.
The second function, sometimes called 'mutation', increases variance so that future populations can exhibit skill variants that were not exhibited by the parent population. This process of inventing and creating new skill variants is important for allowing evolution to come up with better solutions to natural challenges, skill variants that were not present in the root population.
The third function, copying the skill from individuals in the parent generation to individuals in the offspring generation has two parts, both regarding an information-processing capability representing the skill. The first is that the skill is more or less permanently installed in the brain, ready to produce skilled behaviour. The second outcome is that the individual has the capacity to pass the skill to the next generation.