Modern humans generate more neurons during brain development than the Neanderthals, which could have given them an advantage over them, contributing to the underlying cognitive differences between the two.
That increased neurogenesis responds to a single genomic change in a single amino acid in the TKTL1 protein of modern humans, according to a study by researchers at the Max Planck Institute and the University of Dresden, Germany, published this week Science.
The increase in brain size and the production of neurons during brain development are considered important factors for the increase in cognitive abilities that occurred during evolution.
Although modern humans and Neanderthals developed similarly sized brains, little is known whether neuron production during development might have been different, an aspect the study authors explored.
The team found that the modern human variant of TKTL1 protein differs in one amino acid from Neanderthal, which increases a type of brain progenitor cells called basal radial glia, responsible for generating most neurons in the developing neocortex.
Cognitive abilities
The outer region of the cerebral cortex – the neocortex— is an evolutionarily advanced structure responsible for the Cognitive abilitieswhich is clearly large and complex in humans, which is believed to endow our species with unique cognitive abilities.
As TKTL1 activity is especially elevated in the frontal lobe of the human fetal brain, the researchers conclude that this single amino acid substitution underlies the increased production of neurons in the frontal lobe of the developing neocortex in modern humans.
The team, led by Anneline Pinson of the Max Planck Institute, introduced the modern human or Neanderthal variant of TKTL1 into the neocortex of mouse embryos and found that the basal radial glial cells enlarged with the modern human and therefore contained more neurons.
He then explored the relevance of these effects to brain development. In modern humans, TKTL1 contains arginine, while in Neanderthals it is the related amino acid lysine.
The researchers replaced lysine with arginine in human brain organoidswhich are miniature organ-like structures that can be grown from stem cells in the laboratory and mimic aspects of early human brain development.
We found that the Neanderthal-like amino acid in TKTL1 produced fewer basal radial glial cells than the modern human type and, as a consequence, also fewer neurons.
“We found that the Neanderthal-like amino acid in TKTL1 produced fewer basal radial glial cells than the modern human type and, consequently, fewer neurons,” explains Pinson.
“Although we don’t know how many neurons the neanderthal brainl, we can assume that modern humans have more neurons in the frontal lobe of the brain, where TKTL1 activity is higher than in Neanderthals.”
The study implies that neuron production in the neocortex during fetal development is greater in modern humans than in Neanderthals, especially in the frontal lobe, so the researcher considers that “it is tempting to speculate that this promoted modern human cognitive abilities associated with the frontal lobe.” .”
As indicated in a supplementary article in Science“These observations pave the way for discovering evolutionary changes specific factors that shaped the modern human brain and may also help us predict the next steps in its evolution.”
Reference:
Anneline Pinson et al. “Human TKTL1 implies greater neurogenesis in the frontal neocortex of modern humans than Neanderthals”. Science (September 2022)