Following the theory of punctuated equilibrium, many argued that major developments in mammalian (including human) evolution in Africa were timed with large and sudden changes to Earth’s climate. Others have provided evidence suggesting the contrary, that human and faunal evolution were gradual and continuously changing. Now, a new large and in-depth analysis of the eastern African fossil record by Faysal Bibi (Museum für Naturkunde Berlin) and Wolfgang Kiessling (Museum für Naturkunde Berlin and University of Erlangen-Nürnberg, Germany) provides support for the gradualistic view.
The new study examined the rate of species originations and extinctions, as well as faunal compositions, species durations, and body mass in eastern Africa between about four and one million years ago (the late Pliocene and early Pleistocene). The authors found that in all these aspects – turnover, faunas, and body mass – changes were constantly taking place. This means that evolution was not restricted to short intervals, nor were sudden global climatic changes the main cause of species extinction in the past. Rather, major changes in evolution (including human features such as brain enlargement, walking upright, or using tools) were part of long-term and continuous evolutionary changes, and not overly influenced by sudden climatic changes. Global climate certainly influenced evolution during this time, but on the long-term, million-year timescale. Local environmental changes (like tectonic) and species interactions (like competition) were probably far more important for determining patterns of species change on shorter, 100,000 year, time scales.
Bibi, F. and W. Kiessling 2015. Continuous Evolutionary Change in Plio-Pleistocene Mammals of Eastern Africa. – PNAS 1504538112
URL: www.pnas.org/lookup/suppl/doi:10.1073/pnas.1504538112/-/DCSupplemental.