Climate change may have driven early human species to extinction

 Sudden climatic changes may are a major 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 modeling and fossil records to see the effect global 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, Heidelberg man, Homo neanderthalensis, and human being.

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 work out the climatic niche for every species – a variety of conditions including temperature and precipitation that are optimal for survival – and the way cosmopolitan the niche area was through time.

The team found that H. Erectus, H. heidelbergensis and H. neanderthalensis all lost a major portion of their climatic niche area just before they became extinct.

“Species are good at surviving once they have an outsized area at their disposal to measure in,” says Raia. But when liveable areas decrease and also the result's small patches that are geographically isolated from one another, species enter what's referred to as an extinction vortex.

The reductions in the liveable area resulted from sudden climatic changes, the team found. H. Erectus, as an example, went extinct during the last glacial epoch, 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 an element, but that even without the presence of our species the effect of temperature change alone may are enough to guide to extinction. Even species with the power to manage their local environment – like wearing clothes or creating fires – were liable to the consequences of global climate change, says Raia.

But gaps in data may compromise the knowledge of the conclusion that temperature change was the first extinction driver, say researchers who weren’t involved in the study.

Aside from Neanderthals, there's scarcely any fossil evidence for the opposite species studied, says Bernard Wood at Washington University in Washington DC. “Individuals belonging to those taxa lived occasionally, and in places, not sampled by the prevailing fossil record,” he says.

“Plus, the primary 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, no matter the cause – whether or not it's 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 might give the confusion that the climate niche area was also declining, he says.

“No species that we all know of has ever gone extinct from one mechanism. It’s always a mixture,” says Bradshaw. “For example, within the case of the many megafauna species within the late Pleistocene, it’s coming to light that there have been lots of interaction effects between human hunting and temperature change.”