From 48 to 46 Chromosomes: Origin of Modern Man

Abstract

It is old-established that the chromosome number in the chimpanzee, gorilla and orangutan was 48 and not 46 as in man. However, cause and effect of such chromosome rearrangement is unknown. A hypothesis has been proposed that natural selection caused merger of two pairs of autosomes into one chromosome. In the changed climate of the East Africa individuals with less amount of chromosomal Q-heterochromatin regions (Q-HRs) in genome were the most adapted. Two pairs of acrocentrics in the genome the common ancestor, which merged into a single chromosome, apparently, carried on their short arms of Q-HRs with a very high frequency, preventing the birth of individuals with a low number Q-heterochromatin. With the merger of these two pairs of acrocentrics into one, the number of autosomes bearing the Q-HRs reduced from nine to seven pairs, as in the modern human. Such chromosome rearrangement resulted in two important consequences: а) chromosomal Q-HRs distributed into seven Q-polymorphic autosomes, so that it was possible to give birth to the individuals with different, including the low, number of Q-heterochromatin; b) in the population individuals with low number of Q-HRs appeared, able to adapt to new, harsher climatic conditions. With the lapse of time, these individuals formed a new population in the new territory, where individuals with a number of chromosomal Q-HRs like the modern natives of Africa, and with the number of 46 chromosomes in the genome began to dominate. Thus, the cause of the origin of the 46 chromosome karyotype from an ancestral 48 chromosome line was natural selection, and an effect was adaptation, i.e. individuals with different, including the low, number of Q-HRs, got the advantage to open up and to colonize new ecological zones of the East Africa.

Why only a man turned out to be the owner of mind?

“…In particular, we have shown that according to the distribution pattern of chromosomal Q-HRs on seven Q-polymorphic autosomes (3, 4, 13-15, 21 and 22), the populations surveyed by us from different regions of Eurasia and Africa do not differ significantly [50]. This may indicate that modern humans may have originated from a single ancestral population [13][14][15][16][17][18][19][20][21][22]. It would be desirable to repeat similar comparative cytogenetic studies on different populations living on other continents.…”

“…Here, the main harmful environmental factor turned out to be cold, which has been haunting and haunting man to this day, because Homo s. sapiens was and remained a single tropical biological species. This problem, as we believe, was solved at the genome level, in this case by changing the number of chromosomes (from 48 to 46), the amount and localization of their heterochromatin regions [22,23]. Some additional clarifications may be required here.…”

“…This new kind of variability armed man with a new adaptive means in his fight against the cold and hot. It turned out that in the new karyotype, chromosomal Q-HRs in individuals in the population are distributed in such a way that as a result of which it became possible to have children with different numbers of Q-HRs with all the consequences for the organism, especially when concerned the level of human BHC (for details see [22,23]).…”