Are Humans Still Evolving?
The average person can hold their breath underwater
for, like, one to two minutes.
But every day on an archipelago in Southeast Asia,
the Bajau people dive down more than 60 meters deep
to catch fish, and they can hold their breath
for more than 10 minutes.
How? That's better.
This ability, it doesn't just come from years of training.
It's thanks to a genetic change in this population.
In other words, it's an example
of very recent human evolution
that makes a group of people better adapted
to their environment.
But what about the rest of us? Are we still evolving?
As humans live longer, die less,
and make more and more tools
to protect us from the dangerous world that we live in,
does that mean we've bypassed that great filter
of natural selection?
What is the future of human evolution?
(light orchestral music)
Hey smart people, Joe here.
The Bajau people sometimes spend five hours a day
holding their breath. I mean, that's more time underwater
than a sea otter. But what's even cooler is how they do it.
So the secret to their superhuman breath holding
is an actual physiological change.
Bajau spleens are up to 50% larger than yours or mine.
You know, the spleen is an under appreciated organ.
It acts like an oxygen reservoir by storing red blood cells,
the ones that carry oxygen.
So a supersized spleen means more oxygen
can get into your bloodstream between breaths.
Other highly adapted diving mammals like whales and seals,
well they have super spleens too.
Now, you and me, we can't just beef up our spleens
by diving a lot. That's not how evolution works.
Bajau divers have lived in a watery environment
for thousands of years.
Somewhere along the way, a genetic change happened
that gave some people there bigger spleens.
Those people ate more, they survived more,
and over many, many generations,
that adaptation became more common.
This is natural selection.
It's a gene becoming more common in a population over time,
because the individuals who carry that gene are more likely
to survive the pressures of their environment.
Since our species showed up,
we've spread to every environment on Earth.
Our ancestors faced countless environmental pressures.
Different foods, different climates,
and once we settled down in large groups,
domesticated plants and animals,
and started building civilizations,
we've had to face a lot of deadly germs.
Because civilization is filthy, y'all.
A lot of people died as a result of those new pressures,
but our ancestors survived,
often because of new and improved versions of genes
that they carried.
Like Himalayan populations whose lungs can breathe air
with 40% less oxygen than what most of us breathe.
Or people in parts of Africa who are more resistant
to the germ that causes Lassa fever.
Or how populations who migrated closer to the poles
developed lighter skin,
to make the most of less intense sunlight at high latitudes,
you know, since our bodies need sunlight to make vitamin D.
And speaking of vitamin D, let's talk dairy. Love the stuff.
Calcium in milk also aids in vitamin D production,
but most animals can't digest milk very well
after they grow up. Losers.
Luckily, for some of us, a genetic change allowed us to keep
our milk drinking ability switched on throughout our lives.
And because milk is a reliable source of protein
and calories, milk drinking evolved independently
in lots of different places.
Changes like these, and countless others
that helped shape our species,
they happened because of natural selection.
Genes becoming more common
because they make it easier to survive.
But today is different.
I mean, humans have invented so many tools.
We've got medicines, sanitation,
environmentally-controlled living pods,
more food than we literally know what to do with.
I mean, name the last time you thought you might be eaten
by a tiger on your way to get lunch, right?
People just don't die as much as they used to.
Human life expectancy has more than doubled
over the past 200 or so years.
And now that almost everyone is surviving past the age
where they can make babies, does that mean natural selection
doesn't apply to us anymore?
Is this the post-Darwin age of humanity?
Have we entered the hyper technological trans-human utopia?
Have we stopped evolving?
No. Because natural selection isn't the only way
evolution happens, folks.
Some genetic changes just become common by random chance.
Let me show you what I mean.
This jar is full of M&Ms;.
Every bag of M&Ms; has this population makeup.
But this population of M&Ms; has a very different makeup
from the original population,
and so will the future population.
And that happened because of a chance event,
when I grabbed a random handful.
Delicious.
I could do that again and again
and I'd get different results each time.
This can happen to genes too.
When random events decide what genes survive
and become more common, not the environment,
that's not natural selection, it's genetic drift.
Let's say a bunch of highly advanced lifeforms live here.
Until a meteor hits. Thanks to random chance,
these ones survive, and over time,
the population looks a lot different.
Or maybe through a series of unfortunate events,
a few of them end up on this island.
What this new population looks like
will depend on the individuals that founded it.
This kind of thing happens with humans too.
If you're from European ancestry, there's a 90% chance,
or more, you got wet, sticky earwax.
If you're Native American or from East Asia,
you've got about a 90% chance of having dry, flaky earwax.
This difference is caused by two different versions
of a single gene. But the type of earwax you have
doesn't exactly give you a survival advantage,
so which version became more common where
is probably just the result of which gene version
was carried by the first humans to migrate to those regions.
Catch my drift? Genetic drift.
But the chance effects of genetic drift are more likely
to be significant in small, isolated populations.
And humans are not that. I mean, we move around,
we share culture, and as we move around
and mix more than ever, genes are mixing too.
So that's decreased the genetic differences
between human populations overall.
And when rare versions of genes do arise,
it's more likely that they'll get diluted out by the mixing.
Humans living longer or dying less
thanks to our awesome inventions
may reduce the effect of natural selection.
Humans moving around, multiplying,
and mixing a lot may reduce the effect of genetic drift.
That means really wild new adaptations like the Bajau's
super spleens are probably going to be less common
in the future. When you put this all together, well,
a lot of people have claimed that as Darwin's ideas
lose their grip on us, and as humans move around
and mix ourselves up, we're going to start looking
more and more alike. But that's not how this stuff works.
Even things like skin color or eye color,
they involve a symphony of dozens of genes all interacting
in a ton of combinations.
I mean, just consider the variation in physical appearance
we already see today in people with mixed ancestry.
People will always be plenty different.
There is one more process, though, that can influence
our evolution apart from natural selection,
and it has to do with how babies happen.
Ask your parents.
Genes don't just randomly find each other.
Individuals have a choice in who they mate with.
If you're attracted to the largest,
fanciest antlers in a herd,
that will lead to fancier antlered babies,
even if fancy antler genes don't necessarily make you
better suited to your environment.
This is an example of sexual selection,
where the genes that survive are tied to who picks who
to do the mating thing.
How sexual selection will impact the future
of human evolution, that's up for debate.
Let's say the things we're attracted to today
are tied to intelligence, and many scientists think
at least some are. That might mean more future humans
that have traits tied to intelligence, like bigger brains,
or a genetic predisposition to watch this YouTube channel.
Again, this isn't genes that help us survive a germ
or our environment, it's genes that may just make us
more sexy. Now, this last part may feel a little bit icky
depending on how exactly you feel about things,
but thanks to our tools, the future of human evolution
may be, in part, something that we can control,
or at least try to. Our species already relies on machines
to survive and thrive, and we're only gonna continue
to rely more on those machines in the future.
Taking more and more power
out of the hands of natural selection along the way.
And we will increasingly not just depend on machines
for help, but one day we're gonna be physically
or neurally integrated with them.
And frankly, no one knows what that will do to our genes
or which ones become more or less common.
With genetic engineering, we now have the ability
to insert custom genetic sequences into living things,
even ourselves, perhaps even pick and choose the genes
that we want our offspring to have.
This is a form of evolution
that really no other species can do.
How big of an influence these future forces have
on our species is also up to us,
but it will almost certainly have some effect.
Evolution is just change.
And that's a process that never stops,
for our species or any other.
Natural selection happens to be just one way
that evolution happens, but there are many others.
So even if our big brains have made it so natural selection
doesn't determine our future as much as it used to,
change is a constant.
You know, it's pretty interesting to think
that we may be the only species on Earth with the power
to determine at least a little bit
of what our future change looks like,
and that is a power that comes with great responsibility.
And also hopefully comes with a cold glass of milk.
And an Oreo.
Stay curious.
Hey what's up guys.
I'm down here in Florida making our next episode.
But before you go, I wanna tell you something that's gonna
make the history buffs out there pretty excited.
PBS has just launched a brand new,
history focused YouTube channel. It's called PBS Origins.
It's gonna be home to a bunch of great new shows,
but right now, you can go check out Historian's Take,
which is a look at history through the lens of pop-culture,
What old cultures can teach us about our own,
and our future. You're gonna love it, there's a link
down in the description where you can go check them out,
and make sure and tell them that I sent you.
All right, we'll see you in the next video.
And as always, a huge thank you to everyone
who supports the show on Patreon. We could not do this
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find out what we're doing behind the scenes,
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before anyone else, click the link down in the description.
I'll see you in the next video.
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