Scientists have a bold new hypothesis for why we’re the only humans left on Earth

Forget language, or smarts, or even our flair for art. Our species represents the last of its kind simply because we’ve pushed into environments others never dared to tread.

Two archaeologists suggest the global domination of a single species of hominin isn’t incidental – Homo sapien’s ability to flourish in extreme conditions was a key factor in our ability to outlast others in the genus.

Patrick Roberts from the Max Planck Institute for the Science of Human History and Brian Stewart from the University of Michigan describe a knack for being “generalist specialists” as the primary reason for our species’ success.

“A traditional ecological dichotomy exists between ‘generalists’, who can make use of a variety of different resources and inhabit a variety of environmental conditions, and ‘specialists’, who have a limited diet and narrow environmental tolerance,” says Roberts.

“However, Homo sapiens furnish evidence for ‘specialist’ populations, such as mountain rainforest foragers or palaeoarctic mammoth hunters, existing within what is traditionally defined as a ‘generalist’ species.”

With around 7.5 billion of us living in just about every ecosystem on Earth’s surface – and a handful high above it – you could mistake us for being a diverse mob.

As far as animals go, however, we’re pretty bland. Our genetic diversity isn’t all that great, and we don’t even have other species in our genus to sympathise with.

That wasn’t always the case. Depending on who you ask, we’ve shared the Homo genus with six other species across the millennia. And those are just the ones we know about.

One by one they’ve all vanished. Around 30,000 years ago, the last of the Neanderthals disappeared, leaving us all on our lonesome.

Exactly why our species persisted when others didn’t is still a complete mystery.

Brain power has traditionally been the simplest explanation, what with our clever tongues, aptitude for symbolic art, and command of technology.

But we’re quickly learning that Neanderthals weren’t exactly the bone-skulled troglodytes we might like to imagine.

They made art. Cooked with fire. They had a rather effective system of social healthcare. What gives?

There’s good reason to suspect their populations simply faded out as our own species streamed out of Africa, replenishing populations as pockets of Neanderthals slowly disappeared.

Roberts and Stewart don’t contest any of that. They think we also need to look closely at the elephant in the room – our modern expanse away from rolling green acres.

“While we often get excited by the discovery of new fossils or genomes, perhaps we need to think about the behavioural implications of these discoveries in more detail, and pay more attention to what these new finds tell us about new the passing of ecological thresholds,” says Stewart.

The researchers support their claim through a review of archaeological studies on human remains and the environments they’re found in, covering a period reaching back some 300,000 years until about 12,000 years ago.

Species of hominins have been making their way out of Africa for hundreds of thousands of years, reaching far and wide around the globe. So the distances we’ve marched aren’t what set us apart.

Evidence of any of our relatives settling far from the ecological niches of warm forests or relatively fertile grasslands is strangely absent, however. Even the robust Neanderthals tended to stick to woodlands and pastures at the edges of colder regions.

As recently as about 45,000 years ago, Homo sapiens were pushing into some pretty inhospitable environments that could once have been described as remarkably dry, hot, or cold.

While that doesn’t prove that other human species couldn’t have lived in deserts or on mountaintops, it is a possibility.

We’re still far from a complete answer explaining why we’ve stayed the course while other hominins went extinct. And the story probably is unlikely to be simple. 

Numerous recent discoveries have forced us to rethink what it means to be human. We no longer think of our origins in a simple cradle of humanity, but rather understand humans are the product of many thousands of years of interactions stretching across the African continent.

Similarly, our past as a generalist specialist might not have a straight-forward origin story, arising out of an accumulation of socially cohesive traits that helped us push further and further out of our comfort zones.

“As with other definitions of human origins, problems of preservation also make it difficult to pinpoint the origins of humans as an ecological pioneer,” says Roberts.

“However, an ecological perspective on the origins and nature of our species potentially illuminates the unique path of Homo sapiens as it rapidly came to dominate the Earth’s diverse continents and environments.”

This research was published in Nature Human Behaviour.

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