Meet The Humans We Shared the Planet With

Back in January, after I relaunched this newsletter, I got a reply from a new reader. Chloe Troub wrote in about a rabbit hole she'd fallen — Neanderthals. ““Did you know we are the 9th Homosapien and existed with Neanderthals and one other Homosapien for a couple thousand years?,” she wrote. Her curiosity sparked mine, and I spent weeks digging through research to learn about our ancient cousins.

What I learned challenges everything I thought I knew about them. Forty thousand years ago, Homo sapiens weren't alone in Europe — we shared the continent with Neanderthals. But this relationship varied dramatically by region. In some areas, we coexisted for millennia; in others, Neanderthals vanished before we even arrived. And it turns out, our histories are quite entwined.

Beyond the Brutish Sterotype

Forget the grunting, club-wielding "caveman" of popular culture. Relatively recent archaeological evidence reveals Neanderthals as sophisticated beings with complex social structures and impressive technological skills. They crafted specialized tools requiring planning and precision. They controlled fire and cooked their food. Recent discoveries even suggest they created art and jewelry — activities once thought exclusive to Homo sapiens.

There’s even evidence they shared emotional connections and rituals similar to our own with the discovery of Neanderthal burial practices at sites like Shanidar Cave in Iraq.

Their brains were slightly larger than ours, though organized differently. According to research from the University of Rochester, Neanderthals' cognitive abilities were highly developed, though with different strengths than our ancestors. The differences in skull shape between the two species had cognitive implications, including the Neanderthals' smaller parietal lobes and cerebellum, areas implicated in tool use, visuospatial integration, numeracy, creativity, and higher-order conceptualization.

The Great Mystery: What Happened to the Neanderthals?

Around 40,000 years ago, Neanderthals vanished from the fossil record. This disappearance coincides roughly with the expansion of Homo sapiens throughout Eurasia, leading to several competing theories:

The Interbreeding Hypothesis

Recent research from the University of Rochester found that "most Neanderthal DNA in modern humans can be traced to a single major period of gene flow, which occurred about 47,000 years ago and lasted approximately 7,000 years."

Professor Chris Stringer of London's Natural History Museum proposes that interbreeding itself may have contributed to Neanderthal extinction: "... this behaviour could have led to the Neanderthals' extinction if they were regularly breeding with Homo sapiens, which could have eroded their population until they disappeared."

The Disease Transmission Theory

In a 2019 study published in Nature Communications, Stanford researchers suggest that diseases carried by modern humans may have devastated Neanderthal populations.

"Our research suggests that diseases may have played a more important role in the extinction of the Neanderthals than previously thought,” said Gili Greenbaum, postdoctoral researcher at Stanford University. “They may even be the main reason why modern humans are now the only human group left on the planet.”

Climate Change and Environmental Pressures

The period of Neanderthal disappearance coincided with severe climate fluctuations. Although they were cold-adapted, rapid environmental changes may have stressed their adaptive capabilities beyond the breaking point.

The Inbreeding Problem

Small, isolated Neanderthal populations may have experienced detrimental inbreeding. Analysis of DNA from remains at El Sidrón in Spain revealed evidence of "pairings between half-siblings and/or uncle/aunt and niece/nephew," potentially weakening their resilience to other challenges.

The reality of their extinction likely involves a complex combination of all these factors — a perfect storm that Neanderthals couldn't overcome.

The Neanderthal Within Us All

If you’re not wowed yet, just wait: The most remarkable part of this story? Neanderthals never completely disappeared. They live on in many of us.

The percentage of Neanderthal DNA in modern humans is "about 1 to 2 percent in people of European or Asian background," while it's "zero or close to zero in people from African populations."

Some of these genetic contributions helped our ancestors adapt to new environments. Neanderthal genes have been linked to:

• Immune system responses

• Skin and hair characteristics adapted to northern climates

• Fat metabolism

• Pain sensitivity

• Adaptations to high altitude

Not all Neanderthal genes were beneficial, however. Some have been associated with increased risk of certain health conditions — including a higher likelihood of developing a nicotine addiction — reminders of the complex legacy of our evolutionary past.

What Does it Mean to Be Human?

The Neanderthal story forces us to reconsider fundamental questions about human uniqueness. If another human species with complex culture, technology, and emotional lives once shared our world — and our DNA — what does that mean for how we define humanity?

Perhaps the most profound lesson from Neanderthals is that human evolution isn't a straight line leading inevitably to us. It's a complex, branching bush with multiple human experiments, of which we are just the last one standing.

As we face global challenges — climate change, resource competition, and cultural conflicts — something is humbling about remembering that another human species once faced similar existential threats and did not survive them.

Next Week’s Curiosity

From falling pods that can shatter skulls to concentrated radioactivity, meet the common ingredient in trail mixes — no, not cashews — that remain one of the world's last truly wild foods.

Thanks for Reading Feed Your Curiosity!

I’m Bryan M. Vance, your guide to the world’s most fascinating stories that make you say, 'Wait, really?' Every week, I dive into mind-bending discoveries and bizarre historical tales that spark your imagination.

Have a curious story to share? Hit reply — I’d love to hear about the rabbit holes you’ve explored!

Stay curious!