In this week’s Sunday Science, lots of stories of genes and evolution: how genes determine very little of the rainbow spectrum of human sexuality, how Britain has a rather worryingly high proportion of people born as a result of extreme inbreeding, how we changed dog brains, and a remarkable fossil of an ancient human relative.
First up, a story that made quite a lot of the news outlets: there is no such thing as a “gay gene”. Now, we pretty much knew this already – for a start, it’s a stretch to have one gene responsible for a complex trait. Even how genes code for the colour of your eyes is more complex than it first appears. For another thing, if sexual orientation were an obviously inherited trait, there would be a more obvious pattern of inheritance running through families. As it turns out, only about 8-25% of sexual behaviour, as an upper limit, can be explained by genetics. It’s not enough to ever be able to pinpoint someone’s sexual orientation from their genes (which is probably just as well, given the societal discrimination LGBT people still suffer). There were some other intriguing tidbits from the study: for example, the heritable component is even less for women than for men. The other is that, in confirmation with what LGBT advocates have said for a long time, there is a clear spectrum of human sexuality. What does influence orientation then? Well, hormone levels in the womb are a likely candidate, amongst other environmental influences. There’s a more detailed perspective piece on the study in Science here, and an excellent website set up by the authors with LGBT and science advocacy groups which explains the study really well. The original research paper is published in Science here, and is open access. Whilst interesting from a scientific point of view, however, it would be nice for human societies to get to the point of accepting the normal variation of human sexuality such that this sort of news isn’t really news anymore.
On to a rather more concerning genetic study now: thousands of people in the UK appear to have been born as a result of “extreme” inbreeding between close relatives, i.e. between first or second degree relatives. (A first degree relative would be a parent or a child, with whom you share half your DNA; a second degree would be those who share a quarter of your DNA, so uncles, grandparents etc.). From a database of 450,000 people, researchers found 125 whose genes suggested they were the offspring of this extreme inbreeding. I know that doesn’t sound like that much, but it would suggest at least 13,000 people across England and Wales if you scale it up (and the researchers argue that they may have underestimated the frequency, due to the nature of the database). I’m trying to resist making those jokes about people from East Anglia and, for this Kentish lass, the Romney Marsh here. Jokes and societal taboos aside, close inbreeding is bad for your health, because it risks the offspring inheriting multiple copies of detrimental gene mutations. It’s associated with stunted growth, cognitive impairment and reduced fertility. Original rather technical study in Nature Communications here (open access).
On the subject of breeding, one of the most remarkable examples of the power of artificial selection (AKA selective breeding: biological traits selected for by humans, as opposed to natural selection) is the extraordinary variety of domestic dogs. They have all been derived from an ancestral wolf population in a mere 15,000 years or so. Amongst other things, this makes them a hugely useful and interesting case study for geneticists. Now, a fascinating study has revealed that, in the course of the generation of different breeds of dogs, we actually altered their brain anatomy.
MRI scans of dog brains revealed significant differences across breeds. Not only that, but changes in brain structure were correlated with behavioural characteristics: six areas of brain networks were linked to traits they were bred for. So for example scent-based hunting dog breeds showed differences in areas of the brain associated with smell, and also communication (for alerting humans). Original study in the Journal of Neuroscience here.
Back to ancient human relatives now, and the study of human evolution, which seems to have a new discovery almost every week, has hit another jackpot: an extraordinary 3.8 million year old skull belonging to an ancient human relative (featured image). The skull belongs to a species called Australopithecus anamensis, which was previously known, but only by bits of jaws and teeth (it usually is teeth with ancient humans: enamel is hard stuff). This species is thought to be the ancestor of Australopithecus afarensis, such as the famous “Lucy” skeleton, a species that is thought to have potentially given rise to our own lineage of Homo. What’s striking is these two species of Australopithecus seemed to have co-existed for a long time before Lucy and her kin took over. It’s also an important finding because it bridges a long gap between the earliest ancestral hominid species, around 6 million years ago, and Lucy, around 2-3 million years ago. The skull has an intriguing mix of more primitive and derived features. You can see a reconstruction of the face here. Two original research papers are published in Nature here and here (paywalled).
And finally, a beautiful video of lightning flashes in Hurricane Dorian, which belies the devastating destruction it has so far visited upon the Bahamas. Dorian is both hugely strong (a category 5 when it hit the Abacos Islands) but, after it hit the Bahamas, it stalled and became very slow-moving, which meant that communities dealt with sustained torrential rainfall and catastrophic destruction. Hurricanes are not only showing an increasing trend towards becoming stronger (thanks to climate change), but, curiously, they are tending to slow down as well, as research published earlier this year found. (News summary of this trend may be found here).
The 3.8 million-year-old cranium of Australopithecus anamensis. © Dale Omori, Cleveland Museum of Natural History, via https://www.mpg.de/13828990/a-face-for-lucy-s-ancestor