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Thursday, February 29, 2024
Dr. Brown: Following in the footsteps of our ancestors
Dr. William Brown. File Photo

To claim that footprints are far more interesting than skulls might seem odd coming from a neurologist who spent a career dealing with diseases affecting the brain and nervous system, with little attention to feet.

The size and shape of the skull tell us much about the evolution of the brain, especially for those regions associated with speech and higher cognitive functions.

By dating what remains of the skull, sedimentary layers surrounding the skull, analysis of whatever other skeletal elements were found, and perhaps analysis of what DNA might be salvageable from within the bones of the inner ear, it’s possible to draw a reasonable picture of where the owner fits in the story of human origins.

Footprints make their producer’s story personal. They speak to where the person was headed, at what speed, whether he or she was alone or in the company of others of their kind and whether they might have encountered other creatures along the way.

Perhaps the most famous footprints were left by an australopith, named Lucy by her discoverers, Donald Johanson, Maurice Taieb, and Yves Coppens. These footprints were dated to 3.2 million years ago.

Several years ago, fossilized footprints were found on a beach on the south coast of Spain dating back 110,000 years, consisting of 20 or so adults walking at a leisurely pace and several children whose footprints suggested they were playing with one another.

Given the date of the prints, they must have been neanderthals and in my imagination, the adults were talking to one another and the children were playing much as we might do in the same place today.

Perhaps the most compelling footprints to me were those of an adult human, probably carrying a child on one hip, found in New Mexico that date back 8,000 years.

The trail of prints suggests the child might have wiggled from time to time or her mother was tired, and the child was allowed to walk on his or her own for short stretches before being picked up and carried in the same fashion again and again.

Adding interest were intersecting prints: one set was probably produced by a woolly mammoth and the other, at another point in the trail, by a giant sloth.

Who were the mother and child? Where were they headed? What became of them? Those are only three of the many questions those prints prompted in me.

Sometimes footprints speak to a larger story, such as those recently discovered in White Sands National Park in New Mexico, which date to 21,000 to 23,000 years ago using radiocarbon dating.

Precise dating is critical here because, until this recent finding, the evidence strongly suggested that migration to the Americas occurred much later – 16,000 to 14,000 years ago, long after the Last Glacial Maximum 20,000 years ago.

By that time, the climate was warmer and a land bridge of sorts would have made migration from Asia to Alaska less challenging than at the peak of this glacial period 20,000 years ago when so much water was tied up in thick ice and the mean sea level was 125 metres lower than today.

The original study was heavily criticized on technical grounds because of the possibility that the samples used to date the footprints using radiocarbon might have been contaminated by sediment and aquatic plants that were thousands of years older.

Hence the recent update study in which a host of precautions were taken to exclude contamination of new samples for radiocarbon dating and optically stimulated luminescence was used to independently date the footprints.

Using both methods, the dates were almost identical to those revealed in the first study.

The significance of this new finding is that modern humans left Asia for the Americas several thousand years earlier than was hitherto thought and smack dab at the peak time for the Last Glacial Maximum when thick ice covered much of Canada, the northern United States, northern Asia and what is now Alaska.

It’s hard to imagine travelling under those conditions, whether across vast icefields, sea or some combination of the two.

That some made it to become North America’s earliest ancestors is a testament to their toughness and intelligence. Probably most travelled in small groups and their food would have come from the sea as it does today in Antarctica.

Even before the advent of modern humans, neanderthals and later versions of homo erectus covered vast continents, sometimes in appalling conditions, in a series of generational steps, and only the hardiest and luckiest groups survived.

Perhaps you understand why I’m so interested in ancient footsteps. Each tells compelling stories, most of which we can only imagine.

And isn’t imagination what makes life worthwhile, whether we’re physicists, artists of all kinds, or just plain curious about the natural world and mind?

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.

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