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Sunday, September 25, 2022
Dr. Brown: Why did neanderthals disappear?

About 100,000 years ago, 36 stocky people walked along a beach in southern Spain leaving footprints behind in the sand which later fossilized.

Most were made by adults and a few by children whose irregular prints suggested they were playing, perhaps even dancing, leaving us to wonder what they might have been talking or even laughing about.

The scene of frolicking children and leisurely walking adults is common enough on almost any beach where families and friends gather together. But it would be another 60,000 years before modern humans set foot in western Europe. These prints were made by neanderthals.

Neanderthals were short, stocky, rugged people who lived in small communities scattered throughout much of Eurasia. They were closely related to modern humans, and another group, the denisovans who lived in East Asia. And with whom, both modern humans and neanderthals sired children and shared genes as did neanderthals with humans, traces of whose trysts may be found to this day in humans outside of Africa.

Until recently little was known about the appearance of denisovans except for a mandible in Nepal – until a skull was rediscovered in China. The large skull, at the upper range for modern humans, was named “Dragon Man” by the Chinese archeological team and dated between 309,000 and 138,000 years ago.

His face was broad, the orbits large and squarish and the overall shape of the skull was longitudinally flatter than the more globular shape characteristic of most modern humans. These and other features suggested to some scientists that this was our first look at a denisovan skull and face. So far, however, we know nothing about the life and culture of denisovans, unlike neanderthals.

For nearly a century after the first neanderthal skull was discovered in the Neander Valley in Germany, neanderthals were cartooned as dimwitted, based on their large brows and stocky appearance, which was considered brutish.

A different behavioural picture emerged in the last few decades. Studies revealed neanderthals buried their dead, created cave art decades before modern humans reached western Europe, fashioned jewelry and at least in one instance built a ceremonial site deep in a cave in the Aveyron valley in Southeast France, which was occupied by neanderthals as early as 174,000 years ago.

This and other evidence suggest neanderthals were capable of symbolic thinking and probably language, and possessed an imagination, which if not quite the equal of modern humans, was still impressive.

They were also survivors who managed to live through several major swings in environmental climate. Yet they, their denisovan close cousins and other contemporary home species in Africa, Indonesia and the Philippines, all disappeared from the historical record, leaving modern humans as the “Lone Survivor” as Chris Stringer so aptly put it in the title of his 2012 book. But why did the neanderthals disappear?

There’s no evidence that modern humans killed them off, at least in any systematic fashion or that humans outcompeted neanderthals for scarce food resources, although that’s a possibility. A recent genetic study from the Max Planck Institute, led by Svante Paabo, suggests another possibility: the number of fathering males may have been reduced to such a low level that there were too few to sustain genetic diversity and fend off the accumulation of harmful mutations, which might have threatened the health of the community.

In other words, neanderthals had become an endangered species for much the same reason in our time that mountain gorillas are endangered or woolly mammoth communities died out roughly t10,000 years ago – inbreeding triggered too many harmful mutations.

This fine genetic study from an excellent institute also suggested that males tended to remain in their natal communities whereas females dispersed to other communities, an arrangement that might have made matters worse if there were too few fathering males.

Of course, the obvious question is why so few fathering males? Or was the quality of their sperm in some fashion impaired? We don’t know, but at least this study suggests some first steps toward solving the puzzle for the neanderthals, leaving all those other now-extinct hominin species as mysteries to solve.

It would not surprise me if Svante Paabo receives a Nobel Prize for his highly original pioneering work in the field of paleolithic genetics as a vital tool for solving the mysteries of human origins.

Coupled with much more precise dating technologies, enhanced techniques such as satellite searches for locating likely sources for fossils and sophisticated methods such as CT scanning and AI for analyzing fossils, the field of paleoanthropology has transformed in the last few decades.

Look for a new series on human origins next year.

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the Infohealth series at the Niagara-on-the-Lake Public Library.