Early humans

Climate change may have caused early human species to become extinct

By Donna Lu

Was Homo erectus extinct due to climate change?

The Natural History Museum / Alamy

Sudden climate changes could have been a major driver of the extinction of early human species.

Pasquale Raia of the University of Naples Federico II in Italy and his colleagues have used climate models and fossils to determine the effects of climate change on the survival of species in our homo genus.

The researchers used a database of 2,754 archaeological records of the remains of several species that lived over the past 2.5 million years, including Homo habilis, Homo ergaster, Homo erectus, Homo heidelbergensis, Homo neanderthalensis, and Homo sapiens.

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They compared these records to a climate emulator that modeled temperature, rainfall, and other weather data for the past 5 million years. The aim was to determine the climatic niche for each species – a range of conditions, including temperature and rainfall, that are optimal for survival – and how widely the niche area was distributed over time.

The team found that H. erectus, H. heidelbergensis, and H. neanderthalensis lost a significant part of their climatic niche area shortly before they became extinct.

"Species can survive well when they have a large area to live in," says Raia. However, when the living area decreases and small geographically isolated spots appear, species enter what is known as an extinction vortex.

The reduction in living space resulted from sudden climate changes, the team found. H. erectus, for example, died out in the last ice age, which began about 115,000 years ago. The researchers suspect that this was the coldest time the species had ever experienced.

The team found that competition with H. sapiens was also a factor for the Neanderthals, but that even without the presence of our species, the effects of climate change alone could have been enough to lead to extinction. Even species that are able to control their local environment – for example by wearing clothing or creating fire – are vulnerable to the effects of climate change, says Raia.

However, gaps in data can undermine certainty that climate change was the main driver of extinction, say researchers who were not involved in the study.

Aside from Neanderthals, there is little fossil evidence for the other species studied, says Bernard Wood of George Washington University in Washington DC. "People belonging to these taxa lived intermittently and in places that were not recorded by the existing fossil record," he says.

"Also, the first appearance date of a taxon almost certainly underestimates the appearance of a taxon and the last appearance date almost certainly underestimates the extinction of a taxon," he says.

As species near extinction, regardless of the cause – be it competition, hunting, or breeding problems – their range necessarily diminishes, says Corey Bradshaw of Flinders University in Australia. If the range of a species were already in decline, this could give the wrong impression that the climatic niche area is also decreasing, he says.

“No species we know has ever become extinct by a single mechanism. It's always a combination, ”says Bradshaw. "For example, in the case of many megafauna species in the late Pleistocene, there were many interactions between human hunting and climate change."

Journal reference: One Earth, DOI: 10.1016 / j.oneear.2020.09.007

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