Name: 4 Ways Humans Are Still Evolving
Uploaded: 2020-04-13T17:27:28.000Z
Duration: 11 min 47 s
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Adverbs of manner

When we think about evolution, we typically think about big changes that happened long

ago: single-celled organisms becoming multicellular, aquatic animals taking their first steps onto

But we often forget that we humans are still evolving.

If you're thinking you don't feel any different, that's because evolution isn't

defined as changes that affect individuals.

Instead, evolution is the process of change in a population across generations.

Now, our anatomy and behavior haven't changed much in at least the past 65,000 years.

If you met someone from back then, you would probably find them recognizably… human.

But we can still spot some things that have changed in ourselves.

And they've helped us live in harsher environments, avoid disease, and even just… get taller.

We've talked before about how drinking milk is pretty new.

Here are four more ways humans have changed recently — or are still changing today.

To most of us, evolution looks like changing physical traits — like a population gaining

But strictly speaking, evolution is defined as changes in the frequency of certain gene

variants in a population over time — the genes that control those traits.

We're actually going to be talking a lot about gene variants in this episode, so for

Except in specific cases, humans all have the same number of chromosomes and the same

basic set of genes, but the exact sequence of our DNA varies from person to person.

That's what we mean when we refer to variants.

Different variants of a gene are referred to as alleles of that gene.

Those alleles create the variation that make us different from one another.

And if one individual survives to reproduce, those alleles can be passed on down to the

next generation, causing their frequency to increase over time.

Since evolution is basically a change in gene frequencies, one way to tell if a population

has adapted to harsh conditions is to look for an increase in the frequency of alleles

that help you deal with those conditions.

In a 2014 paper, researchers showed that Aboriginal Australians have adapted to living in some

of the world's hottest climates over the course of the last 65,000 years or so.

The deserts of Australia can be really hot — like 45 degrees plus hot!

But humans have lived there successfully for a long time.

In response to increasing temperatures, your body will typically release more of a hormone

And thyroxine has a ton of jobs in your body, like increasing your metabolic rate, helping

regulate your digestive system, and helping to keep your heart functioning.

But too much of it can actually be dangerous if you're in a super hot environment.

However, this study showed that 40% of Aboriginal Australians have a pair of changes in th in

that gene that codes for a protein that normally holds onto thyroxine and releases it when

These variants are associated with lower total thyroxine levels, and lower levels of the

In laboratory studies, this variant cut the temperature-associated release of thyroxine

This might be helping these populations keep their cool in warmer climates.

If something nasty is present in the environment, a population might adapt over time to resist

So one way we can look for evidence for human evolution is by checking for genetic changes

that accompany some environmental variable.

At this point, we should stop and explain why that sentence is phrased like that: the

See, not all gene variants actually do anything.

A gene variant can be something as small as a single nucleotide.

If that single-nucleotide change is in the right place, it changes the instructions in

that gene slightly, and makes the protein it codes for do something a little different.

But if it's somewhere else, either within a gene or nearby, it may not do anything.

We can spot those variants when we sequence DNA.

But a sequence alone doesn't tell you if it's one of those functional variants, or

In the Andes mountains, some indigenous populations are routinely exposed to naturally-occurring

And arsenic is very bad for you, causing issues from skin lesions to cancer.

But people who live in this area seem to process arsenic a bit differently.

If someone's exposed to arsenic, their body will try to deal with it, producing a chemical

called monomethylarsonic acid in their urine.

But people from these Andean populations have less of it than you'd expect.

This suggests that they might have some kind of adaptation that protects them from arsenic

So in 2015, researchers from Sweden looked at these populations in a type of study called

a Genome Wide Association Study, or GWAS for short.

This is a widely-used study design that separates groups of people based on some characteristic

And it combs through their DNA, looking at millions of specific places to see if certain

gene variants show up more often in one group compared to another.

If so, it could be evidence that those variants are tied to the trait in some way.

They don't say anything about whether the variants cause the trait, though.

Basically, there's definitely something going on — but while the study tells you

that a gene variant occurs more often in that group, it doesn't tell you for sure what

The researchers found that these Andean people were much more likely to have specific variants

associated with a gene involved in arsenic processing, called AS3MT.

It's likely that specific alleles of the AS3MT gene help people tolerate arsenic in

The study doesn't tell us how, but it points us there.

And since evolution is a simple change in the genetic makeup of a population, this population

seems to have evolved better arsenic tolerance.

It's likely that a few of the early settlers in this region had this allele, and it allowed

them to be healthier and have more children in a region where the water's mildly poisonous.

So that gene would have spread through the population.

What's more, this would have happened within the last 11,000 years — not that long ago

If an allele is being strongly selected for in a population, it might bring its whole