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Thursday, March 30, 2023
Dr. Brown: Differences between Neanderthal and human brains
As one might expect, evidence suggests Neanderthal brains were not as capable as those of modern humans. PIXABAY

Neanderthals lived between 30,000 and 400,000 years ago and then, throughout their wide Eurasian range, disappeared for mysterious reasons.

Genetic studies suggest they probably lived in small, widely scattered groups.

That mode of living would have fostered inbreeding, progressive loss of genetic diversity, the accumulation of faulty genes – and eventually, their demise.

Neanderthals mated with their close cousins, the denisovans, as well as modern humans, leaving traces of their DNA in present day Europeans but not those living in Africa.

The DNA of the denisovans is found in peoples of East and Southeast Asia, including Australian aboriginals.

From the beginning, Neanderthals were cartooned as brutish crude characters because of their thick bones and heavy eyebrow bones. And for a long time, they were thought to be incapable of symbolic oral language and creating art.

The latter turns out to be wrong because there is evidence that Neanderthals living in Europe created decorative art and left their handprints and some figurative art on cave walls thousands of years before modern humans reached Western Europe.

Even so, Neanderthals left nothing like the wealth of figurative art found in many caves throughout Europe depicting the animals modern humans encountered between 10,000 and 40,000 years ago. This leaves some to wonder if the Neanderthal brain was as cognitively capable as that of modern humans.

The shape of the skull hints of what the shape and possibly functional capacities of the underlying brain might be. The volume of the average Neanderthal brain is roughly 100 to 200 cc larger than the human brain. But the shape of the human and Neanderthal skulls, and hence the underlying brains, are very different.

The Neanderthal skull is flattened longitudinally, the forehead slopes back and there is a noticeable enlargement at the back of the skull, the occipital bun, not found in the human skull.

The orbits and the canal for the optic nerves are also larger in the Neanderthals than modern humans.

The latter three, the larger orbits and optic nerve canal and occipital bun, suggest a larger visual system, but the sloping forehead and longitudinal shape compared to the far more globular shape of the human skull, and the upright forehead suggests the human neocortex in the frontal and temporal regions may be significantly larger than Neanderthals’.

What be to see whether there are any significant differences in the development of the Neanderthal and human brains. Development of the normal brain from progenitor cells is a highly choreographed, precisely timed, and complex affair leading to the creation of the neocortex, all under exquisitely timed genetic control.

Great strides have been made in tracking the genetic and cellular developmental process in the human brain by the creation of human mini-brains and gene editing.

Adult skin cells may be reverse-engineered to create stem cells and then re-engineered to create the earliest progenitor cells which in turn, create brain cells and guide them to their destination. Within a matter of a few days, these tiny several millimetre-sized minibrains develop layered neocortex similar to that found in a normal human brain at an early developmental stage.

Investigators found one protein encoding gene called TKTL1, which plays a key role in the development of the fetal brain. Neanderthals and modern humans share this gene, with a difference.

The protein product of the gene differs between the two species by a single amino acid.

If the Neanderthal version of the gene is substituted for the human version of the gene in normal human minibrains, fewer nerve cells and connections are made. Or if the human version of the gene is introduced into Neanderthal minibrains, more nerve cells and connections are created.

That’s a startling result for one gene and suggests the brains of Neanderthals were not as capable as those of modern humans.

And it reminds us that small changes in single genes can have profound consequences for the brain’s development and potential.

This year the Nobel Prize in medicine or physiology was won by Svante Paabo for his pioneering work on ancient DNA, beginning with mitochondrial DNA and later nuclear DNA from Neanderthals.

He showed how their genomes differ from ours and from a species, the denisovans, that he was the first to identify, using DNA salvaged from a finger bone, which showed they were close cousins of the Neanderthals.

The technology has been used to explore the relatedness of other species and track the evolution and migrations of our own species.

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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