They dead.

5 theories on why Neanderthals went extinct

There's a reason we're the only humans left on Earth.

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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.

So what killed off the Neanderthals? It's possible that it was one thing, but more likely a combination of many. Here are 5 theories:

1. Climate change

A 2018 study argues that climate change played a role in their extinction. Analysis of stalagmites revealed that between 44,000 and 40,000 years ago, there was a series of extremely cold and dry spells. When compared to archeological records, there was an absence of Neanderthal tools dating to those harsh weather periods. This suggests that the European Neanderthal population was much smaller during cold periods, and could explain why they eventually died off.

2. Inbreeding

A common thread through extinction theories is that Neanderthal populations were small. This drove close relatives to mate. Significant homozygosity — getting the same version of a gene from mom and dad — has been found in a number of DNA, as well as skeletal abnormalities.

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

In 2019, scientists hypothesized that a reason why the Neanderthals died out is an ear infection common in children. Modern-day kids get ear infections because their inner ear tubes are short and shallow — the sort of environment harmful bacteria loves. Most kids grow out of ear infections after the age of 5. However, it looks like Neanderthal ear tubes never matured.

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.”

"It was not a cataclysmic event, but a gradual one."

Samuel Marquez, associate professor, SUNY Downstate Health Sciences University.

4. They didn’t adapt

It’s known that Neanderthals were capable of cultural expression and community care-taking. Because we Homo sapiens are capable as well, that indicates that these capabilities can’t be the reason we survived and Neanderthals did not.

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

The most recent theory as to why Neanderthals went extinct goes like this: They were doomed from the start.

Computer modeling indicates that the continuous migration of modern humans from Africa to Eurasia meant they were always going to replace Neanderthals, regardless of the other factors that certainly didn’t help them survive. It was a numbers game, and the numbers weren’t there for the Neanderthals.

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.

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