Climate change likely played a major role in driving early human species to extinction, according to a modelling study published on Friday which researchers said serves a "thunderous warning message" to humans today.
Of the six or more different species of early humans, all belonging to the genus Homo, only Homo sapiens have managed to survive.
The study, published in the journal One Earth, combined climate modelling and fossil record to search for clues to what led to all those earlier extinctions of our ancient ancestors.
"Our findings show that... past Homo species could not survive intense climate change," said Pasquale Raia of Universita di Napoli Federico II in Italy.
This is despite technological innovations including the use of fire and refined stone tools, the formation of complex social networks, and -- in the case of Neanderthals -- the production of glued spear points, fitted clothes, and a good amount of cultural and genetic exchange with Homo sapiens, Raia explained.
"They tried hard; they made for the warmest places in reach as the climate got cold, but at the end of the day, that wasn't enough," he said.
The finding may serve as a kind of warning to humans today as we face unprecedented changes in the climate, the researchers said.
To shed light on past extinctions of Homo species including H. habilis, H. ergaster, H. erectus, H. heidelbergensis, H. neanderthalensis, and H. sapiens, they relied on a high-resolution past climate emulator, which provides temperature, rainfall, and other data over the last 5 million years.
The team also analysed an extensive fossil database spanning over 2,750 archaeological records to model the evolution of Homo species' climatic niche over time.
Their findings offer robust evidence that three Homo species -- H. erectus, H. heidelbergensis, and H. neanderthalensis -- lost a significant portion of their climatic niche just before going extinct.
This reduction coincided with sharp, unfavourable changes in the global climate, the researchers said.
In the case of Neanderthals, things were likely made even worse by competition with H. sapiens, they said.
"We were surprised by the regularity of the effect of climate change," Raia said.
"It was crystal clear, for the extinct species and for them only, that climatic conditions were just too extreme just before extinction and only in that particular moment," he added.
The researchers noted that it is worrisome to discover that our ancestors, which were no less impressive in terms of mental power as compared to any other species on Earth, could not resist climate change.
"And we found that just when our own species is sawing the branch we're sitting on by causing climate change. I personally take this as a thunderous warning message.