Biology / The Student

DNA piece found for human evolutionary puzzle

Originally published in the Student, November 2012.

Christmas DNA

Photo credit: Kevin Dooley

Human evolutionary history has received a missing link in the discovery of a gene unique to humans.

This gene, called miR-941, is thought to have emerged between six and one million years ago, after human and ape evolution emerged.

A team of researchers from the University of Edinburgh compared the human genome, using publicly available data, to that of eleven other species of mammal, including great apes (chimpanzee, gorilla, orang-utan) as well as more common mammals (rat, dog, opossum) to study the differences between them.

As human and chimpanzee DNA show 94 per cent similarity, it has so far been challenging for researchers to find genes that are only found within our species. Most of the 6 per cent difference is within non-coding or ‘junk’ DNA, the functions of which are quite obscure, though they are thought to act as switches for other genes.

miR-941 is the first gene unique to humans that has been shown to have a function, and studying these functions gives scientists an insight into what makes humans so different to the rest of the animal kingdom.

The gene is expressed in many regions of the human body, including the liver, womb and prostrate, but of the most importance is its expression in the brain.

It is highly expressed in the cerebellum (which is involved with motor control eg. Coordination as well as possibly attention, language and fear/pleasure responses) and prefrontal cortex (which affects complex behaviour, personality expression and decision making).

Researcher Dr Martin Taylor, who led the study at the Institute of Genetics and Molecular Medicine at the University of Edinburgh, said “As a species, humans are wonderfully inventive – we are socially and technologically evolving all the time. But this research shows that we are innovating at a genetic level too.

“This new molecule sprang from nowhere at a time when our species was undergoing dramatic changes: living longer, walking upright, learning how to use tools and how to communicate. We’re now hopeful that we will find more new genes that help show what makes us human.”

The effect of this gene’s expression has not been determined yet, but it is thought to be responsible for the differences in brain developmental growth seen between humans and other primates. Future studies involving intelligence and personality could be used to determine the effect of this gene on higher brain functions.

Although one to six million years is a long period of time compared with the human lifespan, scientists say that this is a startlingly brief interval of evolutionary time for this gene to emerge and become active.

According to Dr Martin Taylor, the gene emerged from an area dubbed as ‘evolutionarily volatile’ where mutations that speed up evolution are more likely. However, he told The Student that “The mutation was a role of the dice. But on top of that, the ancestral hominin species that it occurred in was the right environment for miR-941 to provide some form of competitive advantage.

“It clearly wasn’t all good though when it arose, as some genes appear to have responded to miR-941’s birth by changing their sequence so they can avoid regulation by the new gene. Whatever competitive advantage it provided then probably outweighed those deleterious consequences of its emergence.”

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