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Welcome back to Our Human Story, New Scientist’s monthly newsletter all about human evolution and the origin of our species.

This month we’re thinking about how evolution is still changing us, and what that might mean for the future of our species.
ONGOING EVOLUTION

shoults / Alamy
We know that evolution shaped our ancestors and our relatives. It drove an increase in intelligence, a capacity for social cooperation and a talent for endurance running (which seems to have passed me by).

Is it still affecting us? Are we still evolving? And if so, what are we going to turn into in the coming millennia?

The question of whether we are still evolving is curious, because it’s both trivially simple and wildly difficult to answer – I’ll explain why in a moment.

It’s also politically tricky. Many people are wary of the idea that humans are still evolving, because it seems to support the idea that one group of people might be “more evolved” than another – with all the horrendous racism and eugenics that
notion has inspired.

To anyone who is wary of that, two points. First, we’re going to think our way through an example of recent human evolution, and it doesn’t map onto any sort of neat advanced/primitive dichotomy – it’s far more nuanced than that. Second, the sort
of horrible people who want to enforce racial hierarchies don’t care about facts, and freely make up their own if reality doesn’t fit their nasty little preconceptions.

With that out of the way, let’s see if we’re still evolving.

GENE VARIANTS
The short answer is that yes, we are. It isn’t controversial, it isn’t up for debate and, in fact, it’s pretty much impossible that we aren’t.

To understand this, we need to think about how biologists actually define evolutionary change. In a population of organisms, gene variants become more or less common over the generations. If one variant of a gene becomes more common than another, that’
s evolutionary change. It doesn’t matter if the genetic change has no effect on the animal’s body or its behaviour: evolution is a change in the frequency of genetic variants.

Iain Mathieson at the University of Pennsylvania put it another way, in a recent interview with me. “When you say ‘Are humans still evolving?’ to a population geneticist, that’s kind of a meaningless question,” he said. “Mutations are still
happening and the frequency of mutations is changing.”

This is the trivial bit. However, there’s a narrower version of the question that’s harder to answer. Is selection happening? That is, are some genetic variants being favoured by evolution, because they’re advantageous – as opposed to just
becoming more common at random?

SELECTION PRESSURE

Lennart Larsen/Nationalmuseet
Mathieson and his colleague Jonathan Terhorst at the University of Michigan used ancient DNA to demonstrate that selection was at work in Bronze Age Britain, within the past 4500 years. Seven regions of the genomes of British people showed clear signs of
selection, and they were all involved with vitamin D and calcium.

What was going on? Vitamin D helps us to absorb calcium, strengthening our bones. Famously, children deficient in vitamin D develop rickets: their bones are dangerously soft.

Helpfully, our bodies make vitamin D when our skin is exposed to sunlight. That was fine for our ancestors living in Africa. However, when people migrated to places like Britain, they found the sunlight was less intense, the days were shorter at certain
times of year and the skies were often cloudy.

This created a “selection pressure”. British people evolved to cope, for instance evolving lighter skin that let through more sunlight, and developing the ability to drink calcium-rich milk in adulthood.

But, and this is crucial, this didn’t happen immediately. Modern humans and other hominins lived in Britain for hundreds of thousands of years, yet this evolutionary shift only happened in the past few thousand. It isn’t certain why, but the earlier
inhabitants were hunter-gatherers who probably got plenty of vitamin D from fish. The evolutionary shift only happened when people took up farming, so they ate a lot of grains and not as much fish.

FUTURE EVOLUTION
This is one of the most spectacular and well-documented examples of evolution at work in recent human history. I think it ought to convince you that selection is still changing us. Even today, in Chile one population is evolving the ability to digest
milk. Similarly, Mathieson was involved in a genetic study back in 2020 that points to ongoing selection, and a recent Nature paper by another group presents further evidence.

What is going to happen next? Plenty of people have tried to predict the future of human evolution, and they’re all wrong, so you’re now going to get (to quote Tim Minchin) one of my rare but fun rants. Writing in The Conversation, dinosaur
specialist Nicholas Longrich recently offered the following:

“We will likely live longer and become taller, as well as more lightly built. We’ll probably be less aggressive and more agreeable, but have smaller brains. A bit like a golden retriever, we’ll be friendly and jolly, but maybe not that interesting.�
��

Palaeoanthropologists were less than thrilled with Longrich’s latest venture out of dinosaurs and into human evolution, as you can see from this Twitter thread, which starts with “Oh dear God. He’s at it again”.

You’ve probably seen similar speculations in the media from time to time, suggesting that our brains will get even bigger, or we’ll split into two species like in The Time Machine, or whatever.

To all this, I say: just, no. I think it might be possible to make intelligent predictions about how some species will evolve, but there are some that it just isn’t possible for, and humans are one of them.

That’s because humans, like many animals, have cultures: socially determined behaviours. Our future evolution will be shaped by a complex interplay between cultural choices, technological innovation and environmental change. All of those things are
pretty unpredictable, as anyone who has tried to forecast when we’ll have working nuclear fusion knows all too well. Plus, all three influence each other. That’s a recipe for surprises.

Go back to the Bronze Age Britons. They evolved lighter skin and the ability to drink milk as adults in response to the limited sunlight in Britain – but only when they also made a technological and cultural choice (farming) that made them more
vulnerable to those environmental conditions. With the benefit of hindsight and a good dose of biology, it all makes sense. But you could never have seen it coming.

Similar interplays between environment, technology and culture are probably at work in some human populations right now. But good luck trying to forecast which of the many, many competing factors will actually make a difference to our evolution, and
which will prove irrelevant.

In short, I’m pretty much convinced that evolution and selection are still shaping us – but forecasting the results is a fool’s game.

DON'T MISS THIS STORY

Simone Rotella
Lucy Cooke has written a thought-provoking essay about the way sexism has skewed our ideas about animal reproduction. The notion that females are coy, submissive and chaste comes to us largely from Victorian England, but it has proved surprisingly
persistent in zoology and in the study of human evolution. Cooke explains why it is wrong, or at least a wild oversimplification. There are many good evolutionary reasons for female animals to be promiscuous, and they frequently are – but, for decades,
most biologists missed the evidence. The responses to Cooke, and her book Bitch , have been fascinating. I’ve seen (male) biologists asserting that all her examples are unrepresentative oddities, which I guess could be true – but when you find this
many oddities, you have to wonder what the real normal is.

FROM THE ARCHIVE
In the past couple of weeks, there has been a flurry of stories reporting that the human genome has finally been completely sequenced, with hardly any remaining gaps. The study was published in Science at the end of March, but it may well be familiar to
you because I wrote about it almost a year ago, when it appeared as a series of preprints.

People are often surprised to learn that the human genome sequences published in 2001 weren’t actually complete. It’s because so much of the genome comprises repetitive sequences, which are difficult to reassemble if you can only sequence them in
small chunks: it’s like doing a jigsaw that’s all sky. These repetitive bits are sometimes called “junk DNA”, but they may well have been crucial to our evolution. It has taken 20 years of technological improvements to read them properly.

Despite the rafts of data we now possess, we still don’t really understand what a lot of the DNA is doing, or how all the disparate bits interact. That means any efforts to edit the genome should proceed with great caution, if they proceed at all. But
what really fascinates me is what a mishmash our DNA is: thanks to hybridisation, some of our genes come from other hominins like Neanderthals.

Meanwhile, the geneticists are still trying to get a better sequence. The next step is a “pangenome” that is not only end-to-end complete, but also contains information about which bits vary from person to person.

ESSENTIAL READING

Veera/Shutterstock Source: Shutterstock
My colleague Simon Ings has reviewed The Parrot in the Mirror , by zoologist Antone Martinho-Truswell. He says that, in many ways, humans resemble birds. Now, on a surface level we clearly don’t, or I would spend a lot more time airborne. But Martinho-
Truswell argues that there are deeper resemblances. Both humans and birds can live remarkably long lives, which may have created the evolutionary pressure for increased intelligence and complex communities. It’s an intriguing chain of thought, and it’
s certainly true that there are similarities between human language and birdsong. Those commonalities presumably evolved independently, since the last common ancestor we share with birds lived hundreds of millions of years ago.

2022_MAR_Q1_Email_600x400_Pursuit_Chem_Monthly (002).jpg
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1.
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2.
People living on Rapa Nui (Easter Island) relied on freshwater springs under the sea, which were only accessible at low tide.

3.
Unseen notes from one of the first palaeoanthropology excavations reveal the lifestyle and fate of Javanese Homo erectus.
If you’re making plans for May, you might want to leave space on your calendar for the next event in New Scientist’s Being Human series: an online event on Why We Love with evolutionary anthropologist Anna Machin, which will take place on 5 May. Find
out more here.

My new favourite historical figure is Han Yu (AD 768-824), a Chinese politician and poet. He wrote many notable texts, but one of the most unexpected is a proclamation against crocodiles, instructing a particularly dangerous group to leave or be killed.
Researchers have now named an extinct gharial – a close relative of crocodiles – after him.

Thanks for reading,


Michael Marshall

Email me at ourhumanstory@newscientist.com to get in touch
Follow me on Twitter @m_c_marshall and on Facebook @michael.marshall.writer View this email in your browser
This email has been sent to daud.deden@gmail.com

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