If you were a prehistoric human, would you prefer to be able to sprint very fast for short distances or to jog comfortably for kilometres? That's one of the questions thrown up by the so-called "gene for speed," known as ACTN3.
One of the most intriguing genes discovered, ACTN3 encodes a protein
that governs metabolism in "fast twitch" muscle fibres, which generate
force at high speed.
Around 18 percent of the world's population has a truncated variant
of the gene which blocks this protein. The stubby variant, called
R577X, is common among successful endurance athletes, previous research
On the other hand, elite sprinters, who need explosive speed, are
likelier to have the reverse - a functioning variant of ACTN3.
How the study was conducted
The "knockout" mice and ordinary mice with a functioning ACTN3 gene
were put on a motorised treadmill, which spun ever faster until the
luckless rodents were exhausted.
Keen to find out more, researchers led by Kathryn North, a professor
at the Children's Hospital at Westmead, in Sydney, Australia, created a
batch of mice that had been engineered to lack ACTN3.
The easy winners in this endurance test were the knockout mice,
which were able to run on average a third further than their
The apparent reason for this: the loss of ACNT3's protein was
compensated for by a different protein, called alpha-actinin-2, which
shifted muscle metabolism towards a smoother, more efficient, aerobic
Contracted again and again
As a result, fast-twitch leg muscles could be contracted again and
again, without tiring.
North's team also looked through genetic profiles from individuals
of European and East Asian descent and found that there was remarkably
little sign of mutation in the wider stretch of genetic code in the
vicinity of R577X.
Such similarity is a tell-tale sign of what evolutionary experts call
positive selection. Genes which help the fight for survival get
lastingly incorporated in the human genome, whereas those that encumber
it get weeded out.
In other words, the ability to run longer distances became a
preferential trait that became incorporated into a wide swathe of Homo
If so, the incorporation happened recently in human evolutionary history.
According to North's calculations, R577X took root among populations
in central Europe around 15 000 years ago, and in East Asia around
33 000 years ago.
The variant has not been incorporated in all of us, either because
so little time has elapsed for this to happen, or it is being countered by
selective pressures in favour of other genes, they speculate.
The study was published on Sunday in the specialist journal Nature
Genetics. – (Sapa-AFP)
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