Climate variability may not have been a primary driver of human and mammalian evolution, according to a new study from the University of Arizona.
The researchers compared environmental data and the fossil record of large mammals that have lived across Africa for the past four million years. The results contradict the long-held theory that climate change repeatedly caused evolutionary changes in early humans and other mammals.
The Plio-Pleistocene is a period in Earth’s history spanning the last five million years, including the last ice age about 20,000 years ago.
During this period, the researchers observed a long-term trend of increasing environmental variability across Africa. However, this variation did not correlate strongly with species origin or extinction rates, indicating that environmental variability and species turnover are not closely related.
According to Professor Andrew Cohen, first author of the study, the idea that long-term trends towards a wetter or drier climate may have been a driver of human evolution dates back to the time of Charles Darwin. In the late 1990s, a new theory was introduced – the influential variability selection hypothesis.
“The idea here is that it was not just the direction of climate change that was important as a driver of evolutionary novelty in the hominin lineage, but the variability of environmental and climatic conditions,” Prof Cohen explained. . “As our ancestors faced rapidly changing conditions, this hypothesis suggests that they must have been more resourceful and able to deal with many different eventualities, which, in turn, led to the emergence of new species while others have disappeared.”
While the study authors acknowledge that the variability selection hypothesis might still be correct but operating at different scales, they hope to encourage the scientific community to think about the variability selection hypothesis of a more critically – “rather than just accepting it as an underlying principle of how we look at the fossil record in Africa, and in particular the human fossil record,” Professor Cohen said.
“We’re not saying environmental variability isn’t important to human evolution, but the data we’ve currently compiled is highly inconsistent with that idea.”
“If environmental variability were as great as claimed, we would expect to see this long-term trend of increasing variability reflected in the evolutionary turnover of all kinds of species, including hominins, but we just don’t see that.”
The study is published in the journal Proceedings of the National Academy of Sciences
By Chrissy Sexon, Terre.com Personal editor