Scientists have pointed out three genes that may have played a crucial role in an important landmark in human evolution: the noticeable increase in brain size that aided cognitive advances and helped to define the meaning of human beings actually.

These genes, found only in people, appeared between three and four million years ago, exactly before the period when the fossil record shows a dramatic brain enlargement in early familial species in the human clan, researchers said on Thursday.

The three almost similar genes, and also a fourth inoperable one, are called NOTCH2NL genes, emerging from a gene family dating back hundreds of millions of years and greatly associated with the development of an embryo.

The NOTCH2NL genes are specifically active in the neural stem cells reservoir of the cerebral cortex, the outer layer of the brain that is responsible for the highest mental functions like cognition, language, memory, reasoning and consciousness. The genes were found to defer development of cortical stem cells into neurons in the embryo,
leading to the production of a more number of mature nerve cells in this brain region.

“The cerebral cortex defines to a large extent what we are as a species and who we are as individuals. Understanding how it emerged in evolution is a fascinating question, touching at the basic origins of mankind,” said developmental neurobiologist Pierre Vanderhaeghen of Université Libre de Bruxelles and VIB/KULeuven in Belgium.

“It is the ultimate evolutionary question and it is thrilling to work in this area of research,” added biomolecular engineer David Haussler, scientific director of the University of California, Santa Cruz Genomics Institute and a Howard Hughes Medical Institute investigator.

The species Australopithecus afarensis, that is a fusion of ape-like and human-like traits and incorporated the renowned fossil named “Lucy,” lived in Africa at about the time these genes are set to have appeared.

“It would be great if we could sequence Lucy’s genome,” said UC-Santa Cruz biomolecular engineering research scientist Sofie Salama, while recording the unlikelihood of doing that.

The genes are not present in human’s nearest genetic kinfolk since none were found in monkeys or orangutans. An inoperable relative of these genes was found in gorillas and chimpanzees. But the researchers detected the genes in two extinct species in the human clan, Neanderthals and Denisovans.

NOTCH2NL gene abnormalities were found to be connected with neurological conditions containing autism, schizophrenia and both abnormally large and small size head respectively.

The discoveries on the NOTCH2NL genes were given in details in two studies published in the journal Cell.

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