Sudden climatic changes may have been a significant driver of the extinction of early human species.
Pasquale Raia at the University of Naples Federico II in Italy and his colleagues have used climate modelling and fossil records to determine the effect climate change had on the survival of the species in our Homo genus.
The researchers used a database of 2754 archaeological records of the remains of several species alive over the past 2.5 million years, including Homo habilis, Homo ergaster, Homo erectus, Homo heidelbergensis, Homo neanderthalensis and Homo sapiens.
They cross-referenced these records with a climate emulator, which modelled temperature, rainfall and other weather data over the past 5 million years. The aim was to determine the climatic niche for each species – a range of conditions including temperature and precipitation that are optimal for survival – and how widely distributed the niche area was through time.
The team found that H. erectus, H. heidelbergensis and H. neanderthalensis all lost a significant portion of their climatic niche area just before they became extinct.
“Species are good at surviving when they have a large area at their disposal to live in,” says Raia. But when liveable areas decrease and the result is small patches that are geographically isolated from each other, species enter what is known as an extinction vortex.
The reductions in liveable area resulted from sudden climatic changes, the team found. H. erectus, for example, went extinct during the last glacial period, which began about 115,000 years ago. The researchers suggest this was the coldest period the species had ever experienced.
The team found that for the Neanderthals, competition with H. sapiens was also a factor, but that even without the presence of our species the effect of climate change alone may have been enough to lead to extinction. Even species with the ability to control their local environment – such as by wearing clothes or creating fires – were susceptible to the effects of climate change, says Raia.
But gaps in data may compromise the certainty of the conclusion that climate change was the primary extinction driver, say researchers who weren’t involved in the study.
Aside from Neanderthals, there is scarcely any fossil evidence for the other species studied, says Bernard Wood at George Washington University in Washington DC. “Individuals belonging to these taxa lived at times, and in places, not sampled by the existing fossil record,” he says.
“Plus, the first appearance date of a taxon almost certainly underestimates when a taxon appeared, and its last appearance date almost certainly underestimates when a taxon became extinct,” he says.
As species approach extinction, regardless of the cause – whether it be competition, being hunted or breeding problems – their range necessarily declines, says Corey Bradshaw at Flinders University in Australia. If a species’ range was already in decline, that could give the false impression that the climate niche area was also declining, he says.
“No species that we know of has ever gone extinct from a single mechanism. It’s always a combination,” says Bradshaw. “For example, in the case of many megafauna species in the late Pleistocene, it’s coming to light that there were a lot of interaction effects between human hunting and climate change.”
Journal reference: One Earth, DOI: 10.1016/j.oneear.2020.09.007
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Source: Humans - newscientist.com
