Gorillas in the mix for genetics
Then, the line that led to the chimps and us separated from with the one which produced the gorillas. A million years later, the great-ape family tree split again; the chimp branch parted company from the one which would lead to humans. Hominid species have come and gone over the millennia since then. The Neanderthals and Denisovans survived until very recently as did Flores Man, a much more distant cousin. Now, we are the only humans still standing. Our nearest living relatives are the two species of chimpanzee. About a quarter of million pairs of forebears separate us from them.
The ‘bonobo’, only recognised as a distinct species in 1929, is said to be gentler and more civilised than the common chimpanzee. It uses sex and love, rather than brute force and violence, to resolve disputes. We like to think, therefore, that it’s the closer of our two cousins. However, the bonobo line had yet to evolve in the days when our ancestors and theirs parted company, so both chimp species are equally related to us.
The gorilla, being further away on the great-ape family tree, should share fewer genetic traits with us. However, in a paper just published on line in the journal Genome Research, scientists argue that men are closer to male gorillas than was previously thought.
The Y chromosome is found only in males; indeed it is responsible for their maleness. This tiny chromosome is difficult to study, but Kateryna Makova and a team at Pensilvania State University have developed a faster, more efficient, way to unlock its secrets. It’s important to do so if male infertility problems are to be addressed.
The Y carries less than 2% of a man’s genetic material. Unlike all the other chromosomes, it does not undergo genetic shuffling with DNA from the other parent when new chromosomes are being created. Instead, it is passed on unchanged from father to son. All men alive today have the same Y chromosome. Copying errors occur, however, and the extent of these is an indication of the number of generations which separate any two individuals.
Makova’s team examined the Y chromosomes of gorillas chimps and humans. Since humans and chimps have a more recent common ancestor, the Y chromosome of chimps should resemble the human one most closely. The test results showed, however, that it doesn’t. The researchers found that, ‘in many ways, the gorilla Y chromosome is more similar to the human Y chromosome than either is to the chimpanzee Y chromosome’. The chimp’s Y has undergone more changes down through the millennia, and has more repetitive elements in it, than either the human or the gorilla Ys. Men, it seems, are closer to gorillas than we thought.
These findings don’t mean, however, that our nearest and dearest are the gorillas or that our current version of the great-ape family tree is wrong. In 2008, scientists sampled the DNA of a western lowland gorilla in San Diego Zoo and published the species’ genome four years later. Around 70% of our DNA was found to be closer to that of the chimpanzee, while 15% was more gorilla-like. The chimp Y underwent many changes during the seven million years since their line diverged from ours, but the human Y and the gorilla Y did not change as much. Markova suggests that our similarity to the gorilla may ‘be driven by similar mating patterns’. Like humans, female gorillas tend to bestow their favours on only one male, whereas female chimps have multiple partners.
The finding is an important one. If the Y chromosome genes are, at least partly, responsible for infertility, the sources of this condition may predate the split between humans and gorillas all those millions of years ago. Dublin Zoo has gorillas and chimps. The new gorilla island there has become famous worldwide. Why not pay you cousins a visit?
