More than 500’000 years ago, Denisovan, Neanderthal and hominin ancestors not only coexisted but bred common offspring as DNA analyses on bones discovered in the Denisova caves have proven as well as the fact that Neanderthal DNA can be found to this day in humans living outside of Africa, albeit in minuscule amounts. But as evolution progressed, hominins gained an upper edge over the Denisovans and Neanderthals, the latter two became extinct and the hominins continued to survive and ultimately prosper.
Scientists now have an explanation as to why humans acquired a distinct advantage over their extinct cousins: a genetic mutation TKTL1.
In 2014, the sequence of a complete Neanderthal genome was published. Researchers discovered that 96 amino acids differ between modern humans and Neanderthals and initiated studies to investigate if these changes gave humans a definitive edge over the Neanderthals.
Pinson et al. have now reported that that expression of a variant of human transketolase-like protein 1 (TKTL1) increases the number of bRGs in modern humans and thereby the output of upper layer projection neurons.
Without this mutation, humans would have become extinct just like their Denisovan and Neanderthal cousins.
To quote from an article that has been published in Nature ( https://www.nature.com/articles/d41586-022-02895-2
utm_source=Nature+Briefing&utm_campaign=e25edaf388-briefing-dy-20220909&utm_medium=email&utm_term=0_c9dfd39373-e25edaf388-47096220):
“The neocortex, the outer region of the cerebral cortex, is an evolutionarily advanced brain structure that is responsible for cognitive abilities. It has expanded in size and function across the mammalian clade (1). The extraordinary cognitive abilities of humans are thought to rely on brain size (and thus the number of neurons) and the intricate cytoarchitecture of the neocortex. The expansion and folding of the neocortex have been partly attributed to the existence of basal radial glial cells (bRGs). These progenitors generate most cortical neurons, and their number increases in gyrencephalic mammals (which have neocortical folds), such as primates and ferrets. On page 1170 of this issue, Pinson et al. (2) report that expression of a variant of human transketolase-like protein 1 (TKTL1) increases the number of bRGs in modern humans and thereby the output of upper layer projection neurons. This genetic change could contribute to differences in cognition with extinct archaic humans”.
Source: Sara Reardon, Nature | Vol 609 | 22 September 2022 | 665
