Human beings can run long distances because we carry multiple copies of a gene that helps supply our cells with energy, a new study suggests. That supports the idea that endurance running gave our human ancestors an evolutionary edge.
An analysis of DNA from 10 primate species reveals that, compared with the genome of chimpanzees and gorillas, our genome includes many more duplicates of a gene called aquaporin 7 (AQP7), which transports water and sugary compounds into cells. Humans appear to have five copies of this gene, whereas chimps have just two, and other primates carry only one copy.
Humans are believed to possess anywhere from 20,000 to 25,000 different genes. But in some cases, we carry multiple copies of the same gene. And the more duplicates of a gene that exist within a cell, the more protein from the gene that gets produced, according to James Sikela at the University of Colorado Health Sciences Center in Aurora, Colorado, US.
In some cases, though, having an extra copy of a gene can translate into a serious health problem. For example, a given cell normally has two copies of the gene for a brain protein called alpha-synuclein. But people born with a third copy of this gene are predisposed to developing Parkinson's disease.
Given the potential influence exerted by extra gene copies, Sikela and his colleagues wondered how humans might differ from other primate species in terms of the number of duplicates we carry. The team extracted DNA from blood samples taken from various primates including humans, along with chimpanzees, gorillas, baboons, lemurs and several others.
The researchers calculated how many copies of various genes each species carries with the help of DNA "micro-array" technology. If large quantities of the DNA from a given genome attached to certain parts of the micro-array chip, this indicated that it contained multiple copies of a specific gene.
After using this method to screen more than 20,000 genes, Sikela and his colleagues found 84 genes for which the copy number in the human genome differs from that of other primates.
The AQP7 gene in particular caught their attention. The protein made by the gene functions as an important channel in the cell membrane. Specifically, the channel allows water and a sugary compound called glycerol to enter the cell, where they are used to produce energy. This has the potential to make a difference in long bouts of exercise, when the body needs to mobilise energy molecules from fat stores.
Given its role in transporting glycerol, the AQP7 gene "would certainly be a good candidate to be involved in endurance running", says Sikela. He notes that recent studies have suggested endurance running perhaps gave our ancestors an advantage over other primates by enabling them to travel better across sweeping African savannahs.
Sikela hopes that closer examination of the data provided by his new DNA analysis will shed light on how other duplicate copies of other genes might make human development and physiology different from that of other primates.