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 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 .
Our hominoid line, humans, gorillas, chimpanzees and lesser apes, is one among the superfamily Hominoidea.
See the taxonomic table of primates for two comparative classification shcemes.
At the onset of the 20th century, most scientists had accepted the great antiquity of the earth, the theory of evolution and that humanity had evolved from an ape ancestor, but by 1908 the fossil evidence of early man was scarce.
Biologists included principles from genetics in evolutionary theory during the 1920s and 1930s.
Living orders of placental mammals , be it bats, humanity, whales or camels, have as their common ancestor a small insectivore creature that went through a major phase of adaptive radiation during the Early Cenozoic Era .
There are thus two aspects of the human personality, the physical constitution and the spiritual constitution.Social forces appear to have directed much of the evolution of humanity but we are still subject to natural selection.Primate taxonomy (see books: phylogeny, taxonomy, systematics) is in a state of flux due to the discoveries made in primate genetics.( 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.