Neanderthal bones: Signs of their sex lives

Inbreeding leads to a problematically small gene pool.

What Neanderthal bones can tell us about their sex lives
PIERRE ANDRIEU/AFP via Getty Images
In a cave tucked into the limestone hills of the Asturias region of Spain, there lie the remains of a group of 13 Neanderthals that date to between 50,600 and 47,300 years ago.

The site is infamous among anthropologists who study the Paleolithic period for the evidence of what appears to be the massacre and possible cannibalization of a family: Their bones seem to have been hacked at by stone tools and hammers, probably by another group of Neanderthals, to remove their flesh and marrow.

But more importantly, for this story, those bones also reveal something of the sex life of the cave's inhabitants. Anomalies and deformations, along with the DNA buried within their bones, suggest that the members of this group (and their parents) were mating with their close kin.

Lately, much news from the field of paleoarchaeology and anthropology has centered on Neanderthal bedfellows. You would be forgiven for thinking that paleoanthropologists think about little other than paleo-sex. Within the past several years, genetic evidence has emerged that Neanderthals interbred on more than one occasion with both anatomically modern humans and our newfound ancient relative, the Denisovans. One finger bone fragment from Denisova Cave in Siberia is now famous for belonging to a teenage girl who had a Neanderthal mother and a Denisovan father.

But evidence also shows that while some Neanderthals were apparently breeding well outside of the family group, some were also finding mates much closer to home.

In the remains from El Sidrón Cave, paleoanthropologist Luis Ríos and colleagues found 17 examples of congenital anomalies—structural malformations of various body parts that occur while an individual is developing in the womb.

One young El Sidrón individual, for example, had an oddly shaped patella, the bone that forms the kneecap: It had three lobes rather than just one. This Neanderthal probably had a limp. An adult male in the same cave had a markedly narrow nasal passage and a "retained deciduous mandibular canine," writes Ríos and his co-authors—this adult Neanderthal never lost one of his lower canine baby teeth. That tooth developed a painful cyst, which left its mark on the bone of his jaw. Microscopic striations on the tooth itself suggest that he coped with the pain by avoiding chewing on that side of his mouth.

One possible explanation for these skeletal abnormalities is that they resulted from extremely stressful environmental conditions, such as brutally cold weather and scarce food. A pregnant mother experiencing a lot of physical stress and nutritional deprivation might give birth to an infant with some of the same conditions seen at El Sidrón.

Inbreeding leads to a problematically small gene pool

But DNA tests from these bones indicate that inbreeding and a small population size were likely factors contributing to the physical peculiarities in this family. The 13 El Sidrón Neanderthals share much longer segments of their DNA than would be expected if they were the offspring of non-relatives.

Genetically, the three adult males in the group were closely related enough to be brothers, cousins, or uncles, while the four adult females in the group came from three distinct genetic lines. While all individuals were likely distantly related to one another (think third or fourth cousins), it is likely that the males exchanged females with another local, slightly less closely related group.

Today inbreeding carries connotations of "kissing cousins" or intimacy between even closer familial relations. But the term simply means mating between relatives, which increases the number of common ancestors in a family tree and the likelihood of inheriting deleterious genes from those common ancestors. Even third or fourth cousins are genetically similar enough for issues to arise.

The younger El Sidrón individuals (ranging in age from 5 to 15 years of age, along with one infant) were likely the offspring of at least some of the adults. At least one of these children, the young male mentioned above, possessed skeletal malformations that were likely passed down from parents who were fairly closely related.

The tangled familial ties of the El Sidrón Neanderthals are not a unique situation; DNA evidence from other Neanderthals elsewhere in Eurasia also shows elevated instances of shared DNA segments around this time, suggesting that mating between individuals who shared recent ancestors was fairly frequent, and possibly unavoidable, if local populations were small.

In general, inbreeding leads to a problematically small gene pool. Rare harmful traits that might disappear in larger populations tend to be amplified if close kin interbreed. Yet inbreeding has happened throughout human history, especially in the royal families of different cultures. Just look at the Habsburg family line in Spain or the royal families of Ancient Egypt to see the effects of keeping family bloodlines "pure."

Neanderthals were not the only ancient hominins to mate with their close relatives. Anatomically modern humans have also been found with skeletal evidence of inbreeding, such as abnormally bowed thigh bones, deformed arm bones, and even a case of a toddler with a swollen brain case consistent with hydrocephalus.

At the time that these congenital malformations appear, between 100,000 and 50,000 years ago, modern humans were traveling out of Africa. They fanned out across vast geographical regions, and, at times, were quite isolated from one another. Populations might have been separated by hundreds of kilometers at a time, only rarely encountering one another. This might be a simple reason why inbreeding occurred: Pickings were slim.

During the time that the El Sidrón Neanderthal family occupied their cave, it is likely that they were also fairly isolated. Their mating patterns probably had much more to do with small population size and low population density than any sort of cultural practice. There is no way to know if cultural taboos against mating with close relatives existed back then.

Interestingly, most of the individuals in the El Sidrón family group lived well past infancy despite physical conditions that, in some cases, would have made it difficult for them to get around and perform their day-to-day tasks. This family cared for one another, sharing physical burdens and helping each other to survive. Their relations, and their care, are recorded in their bones.

This column is part of an ongoing series about the Neanderthal body: a head-to-toe tour. See our interactive graphic.

This work first appeared on SAPIENS under a CC BY-ND 4.0 license. Read the original here.

A landslide is imminent and so is its tsunami

An open letter predicts that a massive wall of rock is about to plunge into Barry Arm Fjord in Alaska.

Image source: Christian Zimmerman/USGS/Big Think
Surprising Science
  • A remote area visited by tourists and cruises, and home to fishing villages, is about to be visited by a devastating tsunami.
  • A wall of rock exposed by a receding glacier is about crash into the waters below.
  • Glaciers hold such areas together — and when they're gone, bad stuff can be left behind.

The Barry Glacier gives its name to Alaska's Barry Arm Fjord, and a new open letter forecasts trouble ahead.

Thanks to global warming, the glacier has been retreating, so far removing two-thirds of its support for a steep mile-long slope, or scarp, containing perhaps 500 million cubic meters of material. (Think the Hoover Dam times several hundred.) The slope has been moving slowly since 1957, but scientists say it's become an avalanche waiting to happen, maybe within the next year, and likely within 20. When it does come crashing down into the fjord, it could set in motion a frightening tsunami overwhelming the fjord's normally peaceful waters .

"It could happen anytime, but the risk just goes way up as this glacier recedes," says hydrologist Anna Liljedahl of Woods Hole, one of the signatories to the letter.

The Barry Arm Fjord

Camping on the fjord's Black Sand Beach

Image source: Matt Zimmerman

The Barry Arm Fjord is a stretch of water between the Harriman Fjord and the Port Wills Fjord, located at the northwest corner of the well-known Prince William Sound. It's a beautiful area, home to a few hundred people supporting the local fishing industry, and it's also a popular destination for tourists — its Black Sand Beach is one of Alaska's most scenic — and cruise ships.

Not Alaska’s first watery rodeo, but likely the biggest

Image source: whrc.org

There have been at least two similar events in the state's recent history, though not on such a massive scale. On July 9, 1958, an earthquake nearby caused 40 million cubic yards of rock to suddenly slide 2,000 feet down into Lituya Bay, producing a tsunami whose peak waves reportedly reached 1,720 feet in height. By the time the wall of water reached the mouth of the bay, it was still 75 feet high. At Taan Fjord in 2015, a landslide caused a tsunami that crested at 600 feet. Both of these events thankfully occurred in sparsely populated areas, so few fatalities occurred.

The Barry Arm event will be larger than either of these by far.

"This is an enormous slope — the mass that could fail weighs over a billion tonnes," said geologist Dave Petley, speaking to Earther. "The internal structure of that rock mass, which will determine whether it collapses, is very complex. At the moment we don't know enough about it to be able to forecast its future behavior."

Outside of Alaska, on the west coast of Greenland, a landslide-produced tsunami towered 300 feet high, obliterating a fishing village in its path.

What the letter predicts for Barry Arm Fjord

Moving slowly at first...

Image source: whrc.org

"The effects would be especially severe near where the landslide enters the water at the head of Barry Arm. Additionally, areas of shallow water, or low-lying land near the shore, would be in danger even further from the source. A minor failure may not produce significant impacts beyond the inner parts of the fiord, while a complete failure could be destructive throughout Barry Arm, Harriman Fiord, and parts of Port Wells. Our initial results show complex impacts further from the landslide than Barry Arm, with over 30 foot waves in some distant bays, including Whittier."

The discovery of the impeding landslide began with an observation by the sister of geologist Hig Higman of Ground Truth, an organization in Seldovia, Alaska. Artist Valisa Higman was vacationing in the area and sent her brother some photos of worrying fractures she noticed in the slope, taken while she was on a boat cruising the fjord.

Higman confirmed his sister's hunch via available satellite imagery and, digging deeper, found that between 2009 and 2015 the slope had moved 600 feet downhill, leaving a prominent scar.

Ohio State's Chunli Dai unearthed a connection between the movement and the receding of the Barry Glacier. Comparison of the Barry Arm slope with other similar areas, combined with computer modeling of the possible resulting tsunamis, led to the publication of the group's letter.

While the full group of signatories from 14 organizations and institutions has only been working on the situation for a month, the implications were immediately clear. The signers include experts from Ohio State University, the University of Southern California, and the Anchorage and Fairbanks campuses of the University of Alaska.

Once informed of the open letter's contents, the Alaska's Department of Natural Resources immediately released a warning that "an increasingly likely landslide could generate a wave with devastating effects on fishermen and recreationalists."

How do you prepare for something like this?

Image source: whrc.org

The obvious question is what can be done to prepare for the landslide and tsunami? For one thing, there's more to understand about the upcoming event, and the researchers lay out their plan in the letter:

"To inform and refine hazard mitigation efforts, we would like to pursue several lines of investigation: Detect changes in the slope that might forewarn of a landslide, better understand what could trigger a landslide, and refine tsunami model projections. By mapping the landslide and nearby terrain, both above and below sea level, we can more accurately determine the basic physical dimensions of the landslide. This can be paired with GPS and seismic measurements made over time to see how the slope responds to changes in the glacier and to events like rainstorms and earthquakes. Field and satellite data can support near-real time hazard monitoring, while computer models of landslide and tsunami scenarios can help identify specific places that are most at risk."

In the letter, the authors reached out to those living in and visiting the area, asking, "What specific questions are most important to you?" and "What could be done to reduce the danger to people who want to visit or work in Barry Arm?" They also invited locals to let them know about any changes, including even small rock-falls and landslides.

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