The variation of a single protein in the brains of modern humans could be responsible for their superior cognitive abilities compared to Neanderthals, a new study suggests.
The researchers evaluated the effect of a change in a single block of amino acids that is linked to increased production of nerve cells in the frontal lobe of the brain.
“Modern humans differ from monkeys and Neanderthals in this single amino acid change,” say scientists, including those from the Max Planck Institute of Molecular Cell Biology and Genetics in Germany, in the study published Thursday in the journal Science.
The protein, known as transketolase-like 1 (TKTL1), is involved in the production of the brain’s basal radial glia, the workhorses that generate the frontal lobe during brain development, a crucial part of the brain for many cognitive abilities.
While Neanderthals and modern humans have brains of similar size, the researchers say “very little is known” about whether the brains of the two species differ in terms of neuron production during development.
Specifically, they claim that both modern humans and Neanderthals feature brains with a similarly sized neocortex, a brain region known to play a significant role in sensory perception, emotions, and cognition. It is unclear whether this indicates a similar number of nerve cells in the neocortex.
While previous studies have found a small number of proteins that differ between modern humans and our extinct relatives – the Neanderthals and Denisovans – scientists say the significance of these differences for modern human brain development is also unknown. .
In the research, the scientists analyzed one of these proteins – TKTL1 – which exhibits a single amino acid change in essentially all modern humans compared to Neanderthals.
This protein is found in the progenitor cells of the fetus from which all neurons for the most advanced cerebral regions of the cortex derive. Notably, the level of TKTL1 is highest in the frontal lobe progenitor cells of the developing brain.
In modern humans, TKTL1 contains the amino acid arginine in one sequence position, while in Neanderthal TKTL1 it is the related amino acid lysine in this position.
When scientists introduced the modern human or Neanderthal variant of TKTL1 into the neocortex of mouse embryos, they found that a type of progenitor cell believed to be the driving force for a larger brain increased with the modern human variant of TKTL1.
This effect was not observed with the Neanderthal variant of the protein.
As a result, the researchers say, the brain of mouse embryos with modern human TKTL1 contained more neurons.
Scientists conducted another experiment using laboratory-grown human and Neanderthal mini-brains, where they replaced the amino acid arginine in modern human TKTL1 with the characteristic Neanderthal lysine TKTL1.
“We found that with the Neanderthal-type amino acid in TKTL1, fewer basal radial glial cells were produced than the modern human type and, as a result, fewer neurons,” said study co-author Anneline Pinson.
“This shows us that although we don’t know how many neurons the Neanderthal brain had, we can assume that modern humans have more neurons in the frontal lobe of the brain, where TKTL1 activity is higher than that of Neanderthals,” said the Dr. Pinson.
Researchers suspect that modern human TKTL1 increases the synthesis of certain membrane molecules needed to increase the production of neurons in the frontal lobe.
“This study implies that neuronal production in the neocortex during fetal development is greater in modern humans than in Neanderthals, particularly in the frontal lobe. It is tempting to speculate that this promoted modern human cognitive abilities associated with the frontal lobe, ”said Wieland Huttner, another author of the study.