( Adaptive radiation is the evolution from an unspecialised ancestral stock of many different species that adapt to a variety of ecological roles (see books)).Mammals and subsequently humanity may not have become dominant on earth had it not been for the global catastrophe that led to the extinction of the dinosaurs 65 million years ago. Natural selection, gene flow and random genetic drift (the random change in gene combinations with each generation) drive evolution, resulting in a change in gene frequencies within populations . Adaptation is genetically based and so leads to phenotypic changes that accumulate over time;  Speciation (species formation) evolves through reproductive isolation and (genetic) divergence of populations;  Genetic changes through natural selection lead to new species and eventually new taxa .This environment has a living (other animals) and non-living component (e.g. Widgets A unique adaptation usually precedes the entry into a new niche .Tool use by our early ancestors is one such adaptation.Evolution & Ecology " (see its HOME PAGE .) The result is that some areas, such as the glossary are shared.Widgets Human evolution from an ancestral primate species is not a vague hypothesis, but a historical fact.
We humans are first animals, then mammals, then primates.Social forces appear to have directed much of the evolution of humanity but we are still subject to natural selection.