Evolution often seems like something that happened in the past. Yet traits have evolved recently as well, like lactose tolerance in farming populations (within the last 10,000 years). But even that can seem like the distant past from our perspective. Few of us have probably seen the remains left behind by the first farmers, after all.
A lot more of us are probably more familiar with Roman remains. Although still several generations old, these seem much recent from our point of view. Too recent for any evolution to have happened since they were created? No! Using an innovative new technique, researchers have managed to identify a suite of adaptations that have evolved in the last 2,000 years.
This evolution has influenced a range of characteristics, from how tall people are, to our immune systems, and all sorts in between. But what's perhaps most interesting is the technique used to find these developments.
Singletons tell us about evolution
The trick behind this new study revolves around singletons. No, not the person whose "just waiting for the one" but their genetic equivalent. Mutations which have no mate. They're the only version of that mutation in the gene pool. Or at least, the only one in the data set you've got your hands on. They haven't tested everyone to figure out how rare these variants actually are . . . yet.
They're significant because they take time to accumulate.
Imagine a new mutation of a gene arises. At first it might just be one of dozens (or hundreds) other mutations for that gene. Some are more common, others might be singletons like our new mutation initially is. Now, imagine our new gene (lets call him Larry) confers a benefit to his human. That human will are better, making them able to have more children. So over time Larry will become more and more common. If Larry helps his humans enough, he might become the dominant allele in that population (a process known as fixation). Then singleton mutations would start to occur of him.
In other words, evolution and fixation effectively "reset the clock" on how many singleton mutations there are for a gene.
An international group of scientists realised this and began looking at genetic data to find genes with few singleton mutations. These would be the ones that had undergone evolved relatively recently, so wouldn't have had time to accumulate many such mutations. The first phase of this was to conduct a series of simulations and figure out just how "recent" is "recent". After all, as interesting as this technique is it wouldn't be much use if it told us all about the evolution of lactose tolerance in early farmers. We already know about that.
As I gave away at the beginning, these simulations revealed that the length of time it takes a gene to accumulate a typical number of singleton mutations is around 75 generations. Or 2,000 years. Or since the Romans were knocking about. Thus genes which had fewer such alleles (and thus their clock was reset) must have undergone some evolution within these 2,000 years.
What evolved
Looking at the variation in the number of singleton mutations for each gene (quantified as "singleton diversity score") can tell us about very recent developments in our evolution.
But thus far it's only been applied to British people, so it's hopefully relevant to a good chunk of readers since British people have managed to get their genes all over the place. This dataset was chosen because there's a lot of information available about British genomes thanks to the UK10K project. It aims to gather the genomes of 10,000 people in the UK, as the name suggests (scientists aren't the most creative at naming). This same process could be applied to any large dataset, so if you don't have some UK in you just hold on for further research.
Qualifiers aside, what evolution has happened in British genetics since the Romans left?
- There's been increasing prevalence of lactose tolerance. It turns out farmers were becoming better at eating the products of farming. Who'd a thunk it?
- Selection for lighter pigmentation, which ultimately gave rise to the prevalence of blonde hair and blue eyes. Some genes linked to these characteristics were inherited from the Neanderthals. It looks like we were tinkering them with at least another few tens of thousands of year afterwards.
- Many mutations linked to the immune system were spreading throughout the population, likely as British people adapted to their "new" environment. Ancient DNA from other parts of Europe suggests this was going on elsewhere. The entire continent was still adapting the fact it wasn't Africa, thousands of years after we initially arrived.
- A lot of different genes influence height. And a lot of them have been evolving in Britain. Specifically, people have been getting taller.
- Selection for several genes that we don't know the function of. Although they have been implicated in lupus.
In short, British people have evolved to be (more commonly) taller, fairer skinned, healthier (in the UK environment) and with a greater ability to eat milk and cheese. As a British person myself, I'm rather happy with these developments. As a pizza fan, particularly the last one.
The future for singletons
This technique could be applied to pretty much any data set that's large enough to give you an accurate sampling of singleton diversity. Perhaps soon we'll be learning about what recently evolved in other parts of the world too.
At least, assuming this technique is reliable. The key issue is that this paper hasn't actually gone through peer review yet (at the time of writing). It's freely accessible on the biology preprint server. Here's a link for the curious. Without peer review there's some chance a major flaw undermines all their conclusions.
Yet the preprint version has been vetted by many different institutions, including people who know a lot more about it than me. Like Nature. They seem to be pretty good at the whole "science" thing. Whilst they have identified some flaws (many of which were highlighted by the initial authors themselves) the ultimate conclusions seem sound.
So whilst the location this data is coming from might prompt some skepticism, I don't think that pinch of salt is needed. It would be put to much better use making a glass chocolate milk taste better. Which, thanks to evolution, I can digest super well.
Summary
The frequency of mutations has revealed what evolved recently in British people. It turns out they've been getting taller, fairer skinned, and developed more of a fondness for cheese.
References
Field, Y., Boyle, E.A., Telis, N., Gao, Z., Gaulton, K.J., Golan, D., Yengo, L., Rocheleau, G., Froguel, P., McCarthy, M.I. and Pritchard, J.K., 2016. Detection of human adaptation during the past 2,000 years. bioRxiv, p.052084.
