Human Evolution: Overview

Abstract

We interpret human evolution as the changes that took place between 8–5 million years ago and the present within the twig of the Tree of Life (TOL) that connects modern humans with the ancestor we share with chimpanzees and bonobos. Except for the past few hundred thousand years, the evidence in that twig consists of mostly fragmentary fossilised remains, which are samples of the taxa (aka hominins) that existed at the time. For most of the past 4.5 million years our twig of the TOL has contained more than one species, and sometimes several, so in addition to ancestors we also have extinct nonancestral close relatives. But at present, and probably for the past few tens of thousands of years, we have only recovered fossil evidence of one hominin species – modern humans. Key Concepts The tribe Hominini, members of which are called hominins, includes modern humans and their fossil relatives. Human evolution is not envisioned like a ladder, with one species evolving into the next, but like a bush with many branches. Fossils, DNA and, to a lesser extent, stone tools are used to identify fossil hominin species. Early hominins are known from sites in eastern, southern and central Africa. Homo erectus is the first hominin known to have migrated out of Africa, reaching eastern Asia and Indonesia. Modern humans evolved within the past 300 ka and migrated out of Africa by at least 100 ka. Modern human populations outside of Africa include small amounts of DNA from Neanderthals and Denisovans.