Human bodies shaped by ancient viruses millions of years ago: Study

Millions of years ago, vertebrates were infected by an ancient virus which then played an important role in the evolution of human beings' advanced brains and large bodies, according to a new study.

The research, which was published in the journal Cell, studied the origins of myelin which is an insulating layer of fatty tissue that gets formed around nerves and permits electrical impulses to travel at a faster speed.

As per the authors, a gene sequence which was taken from retroviruses, that invades the DNA of their host, is important for myelin production, and that code has now been discovered in modern mammals, amphibians and fish.

"The thing I find the most remarkable is that all of the diversity of modern vertebrates that we know of, and the size they've achieved: elephants, giraffes, anacondas, bullfrogs, condors wouldn't have happened," said senior author and neuroscientist Robin Franklin of Altos Labs-Cambridge Institute of Science while speaking to AFP.

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A team, headed by computational biologist and geneticist in Franklin's lab Tanay Ghosh, went through genome databases in an attempt to find genetics that were most probably associated with the cells which produce myelin.

However, he was interested in exploring mysterious "noncoding regions" regarding the genome which have no obvious function and were earlier dismissed as junk, however, they are now seen as having evolutionary importance.

The research by Ghosh helped him reach a particular sequence which was derived from an endogenous retrovirus, called "RetroMyelin". This has been lurking in our genes for a long duration.

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Faster reactions led to bigger bodies

The researchers then searched for RetroMyelin-like sequences which are present in the genomes of other species and discovered similar codes in jawed vertebrates like mammals, birds, fish, reptiles and amphibians. However, they were missing in invertebrates or jawless vertebrates.

The researchers further concluded that the sequence appeared in the tree of life at the same time as jaws, which came into existence around 360 million years ago in the Devonian period, which is also known as the Age of Fishes.

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"There's always been an evolutionary pressure to make nerve fibres conduct electrical impulses quicker. If they do that quicker, then you can act quicker," said Franklin, adding that is useful for both prey trying to flee and predators trying to catch things.

Myelin also allows rapid impulse conduction without increasing the diameter of nerve cells, because of which they are packed closer together. It also extends structural support which means nerves are free to grow longer, eventually leading to longer limbs.

(With inputs from agencies)