Touching base with our rellos

Those who are not regular readers of Nature (no, not on the top shelf at your newsagents – the world’s leading science journal) may have missed the fact that, as of March, we have a pretty complete DNA sequence of the gorilla genome – to be precise, of a female western lowland gorilla named Kamilah. ‘Why?’ one or two might ask. The mountaineer George Mallory famously wanted to climb Mount Everest ‘because it’s there’. Had he been a scientist he’d have said ‘because we can’, for science is the art of the possible. The limit to advance at any time is what can be done with the available tools. One or two headstrong souls tried blood transfusions – with disastrous results – before we knew how to detect substances on the surface of red cells that define blood groups. Finding the order of bases in DNA had to wait for Fred Sanger’s insight but that has led over the last 20 years to one of the most incredible technical bursts in the history of science. When the project to sequence human DNA got going the cost estimate was $1 per base: the current figure is one millionth of that whilst the speed at which it can be done has gone up by 10 million!!

So the gorilla’s a bargain and the comforting news revealed in its DNA is that chimpanzees are still our nearest relatives: we separated from them, so to speak, 3.7 million years ago but we have to go back to nearly 6 million years to find gorillas going their own way. We’re an evolutionary happy family then, and I’m certainly happy because my ‘other half’ is one of the authors of the gorilla paper. But what has she and her pals unearthed that’s really new?

Two things – well, maybe one and a half at the moment. The first is a side-light on the complexity of evolution. It has indeed turned out that for 70% of the genome gorillas are more distant from us than chimps. Remarkably, the remaining 30% of the gorilla sequence is closer to either human or chimpanzee sequences than these two are to each other. One way this could happen is if there were two variants of an ancestral gene (A & B), either or both that could be transmitted to descendants. Suppose that species divergence occurs to give AA and AB, and subsequently AB separates again to give two species AA or BB. The AA sequence will now be closer to that of the species that diverged two branch points ago than it will be to BB, the result of the most recent speciation.

That’s a quite interesting quirk of molecular biology. But what about the half thing? That’s data that may be useful – but not yet. Every year nearly one million people die from malaria. We get it when mosquitoes inject us with a microorganism called Plasmodium – and so do chimpanzees and western lowland gorillas. Indeed it seems that the strain of the bug that does the damage first arose in Kamilah’s ancestors and since then the mossies have seen to it that the rest of us suffer too – well, almost all of us – because eastern lowland gorillas don’t get malaria. As their name suggests, they’re close relatives of Kamilah: the western branch lives in Central West African countries whilst eastern lowland gorillas prefer the Democratic Republic of the Congo. And we know they’re closely related because the Nature paper sequenced both and showed that the species diverged a bit less than two million years ago. So the key question is: when the detailed sequences are compared will any clues to malaria immunity be revealed? That will take a bit of time and it won’t fix malaria – but it may be one more small step towards being able to control a disease that kills more people than any other bar tuberculosis, AIDS, heart disease and, of course, cancer.