Since Darwin propounded his great theory on the Origin of Species in 1859, refinements have been proposed to our understanding of the operation of evolution.
Rather than selective pressures gradually pushing creatures into new paths that cause slight changes over long periods, many scholars argue that evolution takes place rather rapidly, in short concentrated bursts as a response to major climatic or environmental alterations. These also provide opportunities for creatures to develop new food preferences and habitats.
A crucial period for the development of hominids came around 20-15 million years ago (mya) when the Rift Valley developed in Africa. New ape and hominid species emerged in the millions of years that followed, each adapting to fill a new or newly vacant niche in the environment.
The Australopithecines (from around 5 mya) turned increasingly to ground living, each species eating different plant foods. Early Homo began to scavenge meat, broadening their opportunities for successful foraging.
The hominid brain responded to the demands of complex social interactions, and proved very flexible as an evolutionary tool, deficiencies of the body being compensated by cultural responses operating far more rapidly than would have been possible through biological evolution.
Thus hominids, and particularly Homo, were able to outsmart their competitors in the Struggle for Existence.
