In 1994, the bones of a family of Neanderthals
were discovered in El Sidrón cave, in northwest Spain. They date to around 49,000 years ago, not
long before the final days of the Neandertals. And times must have been tough when this family
lived, because their remains show signs of starvation and nutritional stress throughout
their lives. But their bones also give us other clues that
food might’ve been hard to find… Because, it looks like these 13 Neanderthals
were probably cannibalized. And only a few thousand years after their
deaths, Neanderthal remains no longer appear in the archaeological record - these human
cousins became extinct. So what happened to them? These relatives of ours lived in Eurasia for
more than 300,000 years. They were expert tool makers, using materials
like stone, wood, and animal bone. They were also skilled hunters and foragers,
and may even have created cave art. So what caused the decline and disappearance
of their population? Well, in a way...it could’ve been us. But maybe not in the way you might’ve heard. Our species, Homo sapiens, first arrived in
Europe around 45,000 years ago. And we’re very similar to Neanderthals,
similar enough, even, to interbreed with them. Which we know we did from the small amounts
of Neanderthal DNA that still exist in the human genome today. But only a few thousand years after humans
entered Europe, the Neanderthal population became smaller and smaller before disappearing
altogether. So what happened between us? You might picture epic scenes of our ancient
relatives battling it out for survival - and for good reason. This has been a popular hypothesis for a long
time. It comes up a lot in debates about Neanderthal extinction and has been used to fuel arguments about human nature. But there’s actually very little physical
evidence for direct conflict between these populations. Instead, according to some anthropologists,
the reason for Neanderthal extinction and our survival may come down to a very small difference, based on the humble calorie. Now, a calorie is a unit of energy that your
body takes from the food you eat and uses to power all of the bits and pieces that make
you a living, breathing person. The baseline number of calories you burn in
a day just to keep your body functioning is called your basal metabolic rate. It’s difficult to accurately estimate the
number of calories a person uses each day, but it depends in part on how much muscle
mass that person has and how active they are. The more muscle you have, and the harder you
use it, the more energy your body needs, and the more calories you burn. And this matters because there are a few key
differences between the Neanderthal body and ours. Overall, Neanderthals were a bit shorter than
the average Homo sapiens and they were also probably stockier. Their bones are shorter, thicker, and chunkier
than ours, which indicates that they likely had very dense muscles. The average Neanderthal was probably more
muscular than the average human at the time - or the average human now!. And while both groups lived as hunter-gatherers,
there’s evidence from Neanderthal skeletons that they had a really active daily life,
often doing strenuous activities. For example, the bones of Neanderthal legs
and feet suggest that they were adapted to powerful sprinting rather than long-distance
running. Their two lower leg bones, the tibia and fibula,
are shorter in proportion to their thigh bone than in Homo sapiens. This creates leverage against the ground that
is great for speed, but not as efficient for long jogs. Even their DNA suggests that Neanderthals
were built to be muscular. The Neanderthal genome contains many genetic
variants that, in humans today, are linked to high-level performance in power sports
like weight lifting or shot put. And with those big muscles, Neanderthals probably
burned through a lot of energy. Researchers studying the remains of both Neanderthals
and early Homo sapiens have used their skeletons to estimate how much muscle each would’ve
had on average. And their results suggest that Neanderthals
overall probably had more muscle tissue. This means they’d start off with a higher
basal metabolic rate than Homo sapiens would. So, even if both Neanderthals
and Homo sapiens did the same tasks every day, Neanderthals would still use up more
calories. In fact, according to one study, a Neanderthal
would need to eat a couple hundred more calories per day than the average human - around the
equivalent of an extra hamburger per person per day. Which might not seem like a lot, but think
about it over the course of a year. If ten Neanderthals and ten ancient humans
each ate only hamburgers for a year, the Neanderthal population would need 10 extra burgers per
day, for 365 days--that’s 3,650 extra burgers. In short, a population of Neanderthals needs
more food resources than a human population of the same size to survive, reproduce, and
keep their population numbers up. So picture the scene when groups of Homo sapiens
first make their way into Eurasia. Over the next few centuries, you’ve got
both Neanderthals and Homo sapiens living in the same areas, who need very similar resources
to survive. One group needs more food than the other,
and there’s no grocery store in town. Each group has to hunt and gather for themselves. What’s going to happen? Well, if Neanderthal groups faced competition
for prey or other foods from Homo sapiens, they would be at a disadvantage because of
their need for more calories. And if a population can’t get enough food
to sustain everyone, members of the group will die, and reproduction will happen more
slowly. So, based on this model, when Homo sapiens
populations reached the same areas of Europe where Neanderthals lived, a couple of different
scenarios might have happened. Either the modern humans gradually pushed
the Neanderthals farther and farther south, or groups of Neanderthals and Homo sapiens
mingled together, interbreeding and spreading out further and further over time. And it’s likely that a mix of these scenarios
is actually what happened. We know that Neanderthal DNA entered the Homo
sapiens genome at several points throughout our shared history. Over time and multiple generations, the two
genomes would have blended more and more. And as there were fewer and fewer Neanderthals
around, their genetic contributions to the shared gene pool would have faded into the
background. We also know that sometimes, both Neanderthal
and Homo sapiens populations experienced very difficult conditions, with scarce resources. A major climate shift right after Homo sapiens
migrated into Europe caused long periods of cold, dry climate with severe winters. Those conditions would’ve made it pretty
difficult to be a hunter-gatherer, no matter which group you were from! So if another population of a different kind
of human joined you on the landscape, and was competing for the same resources that
you needed, it would have made it even harder to survive. Neanderthals lived through several other periods
of cold, dry temperatures during the 300,000 or so years before humans arrived, but it’s
possible that their populations just couldn’t survive the combination of cold and competition. We can see evidence of how hard it was for
Neanderthals to survive in glacial periods without competition by looking back at that
family from El Sidrón Cave. They lived about 5,000 years before that big
climate shift, even before Homo sapiens arrived on the scene. And most of the members of that family had
signs in their teeth and skeletons that they had lived a life of pretty constant nutritional
stress. For example, there were defects in the enamel
of their teeth that come from dental development being interrupted by things like malnutrition. Their diet was likely made up of local plants
and animals that they could hunt or scavenge. During colder seasons, food would have been
even more scarce, and they may have endured long periods of near-starvation. This also seems to have been the case for
other groups in the area, because the bones of the El Sidrón Neanderthals have cut marks
and breaks on them that indicate that their bodies were butchered with stone tools. And the only types of stone tools present
are a kind typically made by Neanderthals. Archaeological evidence for Homo sapiens in
that region of Spain doesn’t show up until later in time. So it was probably a different Neanderthal
group, desperate for food, that at least partially consumed the El Sidrón family. And it’s not the only site with evidence
for Neanderthal cannibalism either - this wasn’t an isolated incident. We’ve also found cutmarked Neanderthal bones at sites in France and Belgium. But the fossils from that cave in Spain capture
a particular moment in time - a snapshot of what life might’ve been like for one of
our human relatives. And while this does sound horrifying, it tells us that this local population was probably struggling to survive. The ultimate cause of the disappearance of
the Neandertals is still an open question - and several different causes probably all
contributed. But there’s no doubt that they thrived in
their environments for hundreds of thousands of years. And archaeological evidence shows that they
were making similar tool technologies and behaving in similar ways to ancient humans for a lot of time that the two groups both lived in Europe. So it’s possible that one big difference
between the survival of the two groups might have just been a small unit of energy.
To learn more about what genes our Neanderthal relatives passed down to us, check out our episode, “When We Met Other Human Species”. Become an eonite at Remember, if you're traveling to Bactria, Hump Day is Tuesday and Thursday. And if you need help with this joke, like I did think of a Bactrian camel, that has two humps, not just one And as always thank you for joining me in the Konstantin Haase studio. Subscribe at youtube.com/eons for more journeys through deep time.
