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Infectious Diseases May Had a Role in the Long Process of Evolution

Infectious Diseases May Had a Role in the Long Process of Evolution

(epharmanews)- Mankind was on the verge of extinctions about a hundred thousand years ago. Living humans were reduced to about five thousands all residing in Africa. Modern day humans have all developed from these ancestors and spread around the world replacing the co-existing evolutionary cousins, such as the Neanderthals.

The reasons behind this critical times in which our ancestors’ numbers were reduced remain unknown. There have been many speculations and theories explaining this such as climate changes or volcanic eruptions. A recent study, however, found a rather different reason: humans at that time were victims of infectious diseases that claimed the lives of newborns and threatened the human race with extinction.

In this study, published on June 4th 2012 in the online Early Edition of The Proceedings of the National Academy of Science, an international team of researchers, led by researchers from the University of California, found that a genetic mutation saved our ancestors from extinction by protecting them against this infectious disease.

The study suggests that this genetic mutation inactivated two genes related to the immune system, which might have helped fighting the bacteria, such as Escherichia coli K1 and Group B Streptococci, which attacked humans and caused fatal infections such as sepsis and meningitis in human fetuses, newborns, and infants.

“In a small, restricted population, a single mutation can have a big effect, a rare allele can get to high frequency,” said senior author Ajit Varki, MD, professor of medicine and cellular and molecular medicine and co-director of the Center for Academic Research and Training in Anthropogeny at UC San Diego.

“We’ve found two genes that are non-functional in humans, but not in related primates, which could have been targets for bacterial pathogens particularly lethal to newborns and infants. Killing the very young can have a major impact upon reproductive fitness. Species survival can then depend upon either resisting the pathogen or on eliminating the target proteins it uses to gain the upper hand.” He added.

Researchers found that one gene was missing from modern day human’s genetic map, although it can be seen in chimpanzees, man’s closest cousin.  Researchers were also able to identify a gene that was active in humans but had undergone some modifications, limiting its role to producing a small amount of inactive proteins.  

In a novel experiment, the scientists “resurrected” these “molecular fossils” and found that the proteins were recognized by current pathogenic strains of E. coli and Group B Streptococci. “The modern bugs can still bind and could potentially have altered immune reactions,” Varki said.

“Genome sequencing can provide powerful insights into how organisms evolve, including humans,” said co-author Eric D. Green, MD, PhD, director of the National Human Genome Research Institute at the National Institutes of Health.

It might still be impossible to know exactly what happened during evolution, this study suggests that our ancestors were in grave danger due to infectious diseases more than a hundred thousand years ago, which lead to a significant reduction in their numbers. Only a lucky few survived, because of genetic mutations the most important of which were the above mentioned two genes that might have saved humankind from extinction. Hence, researchers suggest, infectious diseases played a major role in the process of evolution.

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Prepared by: Basel AlJunaidy

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