There's a reason we're the only humans left on Earth.
Some 300,000 years ago, nine human species lived on Earth. Today, Homo sapiens are the only members of our genus left. What happened to the rest of the humans is a paleoanthropological cold case.
Of particular interest is the disappearance of our closest relatives — the Homo neanderthalensis, or Neanderthals, who went extinct 40,000 years ago.
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The first Neanderthal fossil was found in Belgium in 1829.
But it wasn't until 1858 that scientists realized they were dealing with a different type of human.
It all had to do with a skull.
Biologist Ernst Haeckel argued the species should be called Homo stupidus — the "stupid human."
While now there is evidence that they were actually a thinking, feeling people with material culture, that stereotype lives on.
1. Climate change
2. Inbreeding
Dennis Sandgathe, an archeology professor at Simon Fraser University, tells Inverse that the signs that they were regularly mating with closely related individuals “may well have had a direct connection to their disappearance.”
The reason for the inbreeding, Sandgathe reasons, may link to them being at the mercy of their environment.
Something caused their population decline, and this resulted in inbreeding and health issues.
3. A common ear infection
While ear infections didn’t kill off all Neanderthals, researchers think constant sickness puts them at an evolutionary disadvantage. When it came time to compete with Homo sapiens, maybe they didn’t have the energy.
“If you are not as fit, then you would be compromised and unable to sustain your group’s survival,” researcher Samuel Marquez tells Inverse. “It [extinction] was not a cataclysmic event, but a gradual one.”
4. They didn’t adapt
What makes us humans special, scientists argued in a 2018 study, is that we’re “generalist specialists,” a.k.a. we can adapt to ecological niches. And while Neanderthals and other ancient humans migrated far from Africa, they generally stayed in woodland and grassland areas. The study authors argue that fossil evidence indicates it was only Homo sapiens who ventured elsewhere. (Although other paleoanthropologists disagree.)
“We thought, why not turn to the most glaring fact of all?” researcher Patrick Roberts tells Inverse. “That our species is the only one to have colonized the entire globe and all of its environments.”
5. Population replacement
Scientists backed up this idea in a recent study. In their population dynamics simulation, they found that various elements would have driven Neanderthals to go extinct over time, even if they weren’t competing with Homo sapiens for resources.
They attributed their downfall to “random events, rather than to some external factors.”
The reasons for their demise remain controversial, and research is ongoing. Still, you have to question whether, while extinct, if Neanderthals are really gone.
After all, Neanderthal DNA lives on in people living today, the result of ancient trysts and some helpful genes.