Are We Still Evolving? Horizon

Of all the questions that science can ask,

I'm fascinated by one that goes to the very heart of who we are.

It's a question about what's happening to us, as a species,

right now.

The question is, are we still evolving?

We've learned an enormous amount about how we evolved in the past

and became human.

But has the process that made us now stopped?

Or are we still changing?

Across the world, scientists are looking for clues.

And I'm going to join them.

I want to find out what we can learn

from breakthroughs in human genetics...

It's very exciting because we are starting to piece together bits of

information to get this sort of coherent picture of human evolution.

I want to see if extreme environments might have forced us to change.

And I want to find out about a technology that

might change our species forever.

-Do you think this is a good idea?

-I'm not sure if it's a good idea.

But I think trying to remove it as part of

our future evolution is just a task that's not going to be accomplished.

It's here, it's not going away.

We know that evolution made us who we are.

But are we still evolving?

I'm Alice Roberts.

I've studied how we've evolved in the past but now, I want to

know if we're still changing.

To find out, we need to understand how we got here in the first place.

Our story, and the story of all life on earth,

began an unimaginably long time ago.

We can draw this as a massive tree of life, starting around 3.5

billion years ago, and branching and branching and branching.

Now, the vast majority of these branches are going to be

single-celled organisms, many of them bacteria,

and 600 million years ago, animals appear.

So on this tiny bit of this tree of life we're going to have to fit

all of the species of animals that have ever existed on this planet.

And then seven million years ago, our own little part of this tree,

hominins, us and our ancestors, appears.

Our species, appearing about 200,000 years ago,

is the only remaining twig.

On an evolutionary timescale, humans have only just emerged.

So is it possible that we've continued to evolve

since our species first appeared?

Given that it took 3.5 billion years for our species to evolve,

200,000 years is just the blink of an eye.

To find out if we've changed in that time, I want to understand

how quickly evolution can happen.

Evolution is an amazing phenomenon, it explains the huge diversity of

life on this planet, past and present, and without

it none of us would be here.

No humans, no living things, none of this that's around me right now,

apart from the rocks.

And I'm going to see evolution in action.

Tucked away in the rolling, green hills of the Devon countryside

lies a derelict mine.

The surrounding earth has been poisoned.

But the mine has left a surprising legacy,

and Professor Mark Hodson has discovered something that would've

got Charles Darwin very excited.

So, Mark, what is so special about this place?

Well, this is Devon Great Consols.

It used to be a copper mine and then evolved to become an arsenic mine.

And at its peak, they produced so much that when it was stored on

the docks, they used to say that there was enough arsenic

to poison the planet.

So, is it still poisonous today?

In this area and all around we've

measured the arsenic levels and we're talking three orders

of magnitude more arsenic than would be considered safe.

So that's a massive amount of arsenic in the soil.

Oh, yeah, the soil's ooching with it.

And yet despite that apparently lethal level of arsenic, Mark has

found earthworms living in the soil.

But they're not ordinary earthworms.

If you take an earthworm from your garden and put it in this soil,

that earthworm would die very rapidly.

But the worms here have evolved to cope with the poisonous soil.

And we're going to hunt for one.

And you reckon this is a good spot to start?

Yeah, it's moist, there's organic matter,

-there's definitely some soil there so have a spade.

-Thank you very much.

It's not rocket science, this bit.

-Ooh, ooh, ooh, I think I've found one.

-Yeah.

-Look.

-Look, look, look.

-Oh, yeah.

You see if you can get him out.

Quite small, he's a bit anaemic looking.

Yeah, he's quite pale down this end.

Yeah, yeah, almost yellowish.

And that's characteristic of a lot of the worms we find in this area.

But it's not just their colour that's changed.

Mark believes these worms have evolved into a new species.

And it's all thanks to natural selection,

the process that drives evolution, and the process that made us who we are.

So this isn't just

a bog standard earthworm that's managing to survive in this soil?

Well, we've done the genetics on these earthworms

and what we've found is there's a distinct genetic difference.

These earthworms are more distinct from the earthworms in your garden than we are, compared to mice.

That's wonderful.

And what's really surprising is that it only took 170 years for

the worms to change so much.

Well, if you're looking for

evolutionarily advantageous traits, here being able to deal with arsenic

has got to put you at a distinct advantage.

I think so, it doesn't get more clear cut than that.

It is amazing to see an example of evolution happening.

Right, after you...

It's a classic illustration of natural selection in action.

As the levels of arsenic rose in the soil around here,

any worm that was lucky enough to have what was originally a chance mutation

that allowed them to survive,

would do so, and worms without that new adaptation would die.

It's simple, brutal, and effective.

It's also exactly the same process that made us.

And if natural selection can change these worms so quickly,

perhaps it's changed us, since our species first appeared.

But there is something that makes us

very different from any other animals.

Our species emerged some 200,000 years ago.

About 60,000 years ago, we spread out from Africa.

And since then, we've moved to every corner of the planet.

But on the course of that journey, something incredible happened,

something that means the normal rules of evolution

may no longer apply to us.

Tens of thousands of years ago,

our ancestors began to protect themselves from the environment

in a way that no other creatures have managed to do.

They invented things to make life easier...

shelters, tools and other simple technologies that didn't exist

anywhere else in the natural world.

-May I have a hot chocolate, please?

-Certainly, madam.

-Thank you.

So while polar bears evolved thick coats of blubber to cope with

the cold, our ancestors made fires, and wrapped themselves in clothes.

By helping us adapt to new environments,

did our inventions stop us evolving?

Humans are clearly

a product of natural selection, but thousands of years ago

we began to place barriers and buffers between ourselves and the elements

to protect ourselves from the slings and arrows of the natural world.

And that does beg a question: has all our technology sheltered us

not only from nature,

but from natural selection itself?

It's a question that scientists have wondered about

ever since Darwin's time.

Has our culture, our technology, stopped us evolving?

Are we the same as the people that emerged in Africa 200,000 years ago?

It's an incredibly difficult question to answer.

The trouble is, how do we find out if we've changed?

I've come to Oxford,

where there's an ancient clue that might help to unravel the mystery.

Tucked away in the university's Natural History Museum

are the oldest bones of a modern human ever found in the UK.

They were discovered by the Reverend William Buckland, 180 years ago.

It seems that Buckland thought that

these could be the bones of a witch from Roman times

and they're stained with ochre, they have this reddish appearance,

so she became known as the Red Lady of Paviland and the name has stuck.

But we now know that these are not the bones of a 2,000-year-old woman

and I can see very clearly that this pelvis is male.

These are the bones of a man who lived 33,000 years ago.

33,000 years ago was before the peak of the last Ice Age.

When he was alive, the Red Lady of Paviland shared

the planet with Neanderthals, and woolly mammoths still roamed the earth.

So are these bones the same as mine?

Because if they are, perhaps we have stopped evolving.

Now, I'm a physical anthropologist, I've looked at hundreds of skeletons,

but if I didn't know how old these bones were, that they'd been radio

carbon dated to 33,000 years ago,

I'd believe you if you told me they were a few hundred years old.

Of course, there's variation in skeletons, there's variation in

our bodies, each of us will have a different skeleton,

but these bones fit within that modern range of variation.

There's nothing in this skeleton to suggest we've changed

over millennia.

So perhaps our use of technology

and culture really has put us out of reach of natural selection

and halted our evolution.

But if we haven't evolved in thousands of years,

then that would mean that we're all fundamentally the same.

But it's clearly not as simple as that.

You don't need to look around for long to realise that we have all

changed and in a very obvious way.

In the past, we were all dark-skinned.

Now, we're not.

It's a way in which we've evolved apart from each other

since our species emerged.

But it's also long been dismissed as a superficial difference,

no more than skin deep.

The key question is whether we've evolved in more fundamental ways,

beneath the surface.

To find out if we've changed, we need to look in extreme

environments, at people who might have faced natural selection

at its most brutal.

Dr Cynthia Beall believes she's found the perfect place to look

for signs of human evolution -

high in the Himalayan mountains, home of the Nepalese Sherpas.

She's spent much of her life trying to work out

whether they're fundamentally different to the rest of us.

Every time we do a research project here in Nepal or in Tibet, scientists

get excited because we find unusual features of their biology, and that

suggests there is something very interesting and exciting going on.

There's something about this environment

that's potentially lethal, and that's the thin mountain air.

At this altitude it contains dangerously low levels of oxygen.

What makes altitude harder is that every breath full of air has only

about 60% of the oxygen molecules than at sea level.

Now that is an enormous

stress physiologically because every cell in our body needs to get oxygen

regularly in order to generate the energy it needs to sustain life.

So when the Sherpas moved to the moutains thousands of years ago,

did they begin to evolve apart from the rest of us?

Cynthia has come to Namche Bazaar, a small village in Nepal.

At an altitude of 3,500 metres,

it's known as the Last Town Before Everest.

In just the past two days, two foreigners have died nearby

due to altitude sickness.

But the Sherpas, who have been living up here for 10,000 years,

don't struggle with the low oxygen levels.

After decades of research, Cynthia has been the first person in

the world to work out why no locals die from the effects of high altitude.

The first thing she wanted to look at was their blood, because the way

that most of us cope with low oxygen is to raise the numbers of red blood

cells and therefore the haemoglobin

level in our blood, to help draw more oxygen from the thin air.

But those extra cells aren't the perfect solution

to a lack of oxygen.

By thickening our blood they can cause blood clots and even death.

So did the Sherpas' ability to survive at high altitude

have something to do with their haemoglobin?

Someone from low altitude, let's say a young man who had been trekking for

a month out here, would probably have

17.8, 18.5 grams of haemoglobin.

OK, now let's see what Pembola's haemoglobin concentration is.

And he's 16.4.

With these haemoglobin levels, the Sherpas don't suffer

the problems that many of us face when we come to high altitude.

But how could they be getting enough oxygen without

raising their haemoglobin levels?

Once we had established that Tibetans and Sherpas don't have

very high haemoglobin levels, that led us to think about what

are they doing in order to get enough oxygen to their cells,

and we decided that it was time that we took a good look at blood flow.

Using a video microscope, Cynthia was able to look inside the Sherpas'

upper lip to investigate their network of capillaries.

Oh, it looks gorgeous.

Big thick,

it's like a meandering river with lots and lots of little tributaries.

There's a big density that we would not see

if we tested my blood vessels, however.

We wouldn't see so much twisting and turning,

we wouldn't see such wide blood vessels.

Cynthia had made a breakthrough.

The Sherpas have evolved to be different from the rest of us.

Their unique blood circulation delivers them the oxygen they need

without the potentially fatal risks of high haemoglobin levels.

There have been hints for a couple of decades now that something

exciting was happening among high-altitude Tibetans and Sherpas.

The work that we've done gives evidence of evolution by natural selection,

and it has been very satisfying to be able to finally say that.

The Sherpas of Nepal provide clear evidence that some of us, at least,

are different from our ancestors.

There have been changes to the structure and function of our bodies

that are much more than just skin deep.

Although we may have sheltered ourselves from the natural world,

in some extreme environments at least,

humans didn't stop evolving.

And that begs the question, what about the rest of us?

Have we all continued to evolve?

It's a question that technological developments have been able

to shed extraordinary new light on.

I've come to The Broad Institute in Massachusetts,

one of the world's leading genome research centres.

I've studied the effects of evolution in a really traditional way,

by looking at the differences in structure of the human body.

But I don't think it's going too far to say that this place

has totally revolutionised research into human evolution.

Unravelling the human genome was a scientific breakthrough

that many hope will change the future of medicine.

But for Pardis Sabeti, it's done something very different.

It's opened up a window onto our past.

Our genomes contain a wealth of information

about the genetic changes that have happened in our history.

That means Pardis can scan the genome to look for signs of recent evolution,

like the Sherpas' ability to survive at high altitude.

So you're analysing the DNA of people living today,

but you're actually able to detect when changes in their DNA occurred,

going back tens of thousands of years?

Yeah, that's the thing that sometimes

is hard to kind of understand,

but it's essentially that we are living records of our past,

and so we can look at DNA of individuals from today

and get a sense of how they all came to be this way.

By comparing the DNA of thousands of people, Pardis is able to find

examples of genetic mutations that have become common

in just the last few thousand years.

Ultimately we're looking for that rare mutation that somehow is

so beneficial it didn't get lost, and not only did it not get lost,

it started spreading very quickly through the population.

And she's found much more evidence of natural selection than scientists expected.

Now we basically have scanned the genome

and found a lot of places where interesting things are going on.

In this recent study that we did, we had 250 new

regions of the genome that we've identified to be under selection.

And we can start looking at what those parts of the genome are

and what they do, and really get a global view of human evolution.

With 250 areas of our genomes that have undergone recent natural selection,

it's clear that we've evolved away from our ancestors

far more than anyone had ever anticipated.

And the changes to the way our bodies work

tell the story of how our world has changed since our species appeared.

Is there any evidence of adaptation

to different environments as people spread throughout the world?

Yeah, absolutely. So as these populations migrate outside of Africa and went north,

in Europe and Asia you see lots of mutations for pigmentation,

changing your skin colour as you go to climates that have less light.

What's interesting is you see all these different pigmentation mutations

but they're different ones that occurred in Europe and Asia,

and all different populations trying to drive to that.

-And presumably there are lots more?

-Yeah, you see lots of metabolisms,

so changing to diets in all populations.

You see them all over the place. Then we have all sorts of new ones

that we're interested in. In Asia you see hair and sweat,

so something to do with maybe thermoregulation.

And you can see that in very, very recent time,

there's been mutations to high altitude.

And Pardis has found that one of the greatest drivers of our evolution

has been disease.

One of the classic examples is the sickle cell mutation

that protects from malaria

that emerged in Africa sometime within the last 10,000 years.

What is the impact of genetic research like this on our understanding of human evolution?

It's absolutely revolutionised it.

The ability to mine these large data sets and start looking at

many, many people throughout their genomes -

we're at a place now where we can create so many different

hypotheses as to what's driving evolution and get down to

the single unit that changed and then be able to explore that.

Our genomes have given us a phenomenal new source of information

about how the world has changed us.

The major events of our past are written into our genes.

But our genetic history contains a lot of surprises.

There's one development in our history that fascinates me more than almost any other,

and it set us on course for the modern world.

There are few more pivotal moments in our past than when we started farming some 10,000 years ago.

It was to be a defining point in our history.

It would transform our diets, our cultures,

and provide the foundations of our civilisations.

But did its impact run even deeper than that?

We used to believe that our cultural and technological developments like farming would stop us evolving.

By giving us a stable food supply that could keep even the weakest members of society fed

throughout the year, it would distance us from natural selection.

But did farming stop us evolving, or did it just change how we evolved?

To answer that we need to understand

how farming might have affected us 10,000 years ago.

Mark Thomas is a geneticist who's trying to do exactly that.

To do it he's got some volunteers and several pints of milk.

Right, so what we're going to be doing is we're going to be testing

your ability to digest the sugar in milk. The sugar's called lactose.

All babies produce an enzyme in their gut

called lactase which breaks it down.

But about 65% of people in the world,

after the weaning period is over, they can't digest the sugar in milk.

It may give you a bit of diarrhoea, it may give you, sort of,

a lot of flatulence, a lot of farts.

So if you're happy with this and you're happy to go ahead, then, gentlemen, just drink your milk.

If milk can't be digested properly, a lot of hydrogen is produced...

OK, so, deep breath then breathe out nice and slowly.

..allowing Mark to test someone's lactose tolerance

by measuring the amount of hydrogen in their breath.

We've got 31 parts per million.

The higher the reading, the more hydrogen and the less lactose tolerant they are.

Right, so how are you feeling?

There's like a battle going on between God knows who down there.

Other than that...

All right. Do you feel any need to visit the gents?

-If I was to make a guess, I'd say midnight.

-That's good going.

Before we started farming,

every adult on the planet would have had the same reaction.

Ok, so Prav is 200. That's pretty impressive, that is pretty impressive,

those are classic results.

Beautiful results.

Are you sure you don't want to...?

No, I stand by my word about midnight.

I wouldn't make those kind of promises if I was you.

Most of them, they're more or less at the same level as their baseline

before they drunk the milk and they stay at that baseline throughout the whole experiment.

Prav, however, has just sky rocketed, so he's gone from

a relatively low baseline, to something really, really high.

These are absolutely clear cut and typical results for somebody who's a non digester.

For someone healthy, like Prav, lactose intolerance is a discomfort, rather than a serious problem.

But Mark's research shows that for our ancestors,

whether or not you could digest milk into adulthood could be a matter of life and death.

And the lucky few who could, were the evolutionary winners.

It's probably the most advantageous characteristic

that Europeans have evolved in the last 30,000 years.

But milk is only ever going to be a component of somebody's diet,

so why would drinking milk into adulthood be so strongly selected for?

Milk has got lots of energy in it, it's very nutrient-dense, it's got lots of other goodies

like you know, various vitamins and calcium, and so on and so on.

Also it's a relatively clean fluid, so it's much better than drinking

stream water or river water or well water or something like that.

Another advantage is that if you're growing crops

you have a boom and bust in terms of the food supply,

so you have one growth season a year and you have lots, then nothing.

So if you're looking at a population under pressure

where people are struggling to get adequate nutrition,

anybody who CAN drink milk into adulthood will be better off.

Right. The advantage that's been measured is just incredible,

absolutely incredible, how big an advantage it was

for these early farmers in Europe.

The core of Mark's research has been trying to understand

how what happened thousands of years ago,

has determined the genes of people alive today.

And how does the origin of lactase persistence

and its spread throughout these populations relate to farming?

Incredibly well.

Where wee see it we see the people have a tradition of dairying.

It's very common in Europe and particularly in North Western Europe,

so especially in places like Southern Scandinavia, Britain

and probably most, most dramatically in Ireland

where virtually everybody is lactase persistent.

You can see it's very, very low, almost absent in South East Asia.

I think research like this is incredibly elegant and gives us such an insight into our past.

Absolutely. It's basically a hidden world of information.

And that hidden world of information has revealed that rather than

sheltering us from the effects of natural selection,

farming actually drove our evolution.

It appears that changes that we made to our world had as much power

to transform our genes as anything that nature itself could throw at us.

But something fundamental has changed in the last 200 years,

something that might have finally allowed us to escape the pressure of natural selection.

Today, in the developed world, our way of life has changed completely.

If you can't digest milk, you just drink something else.

With our plentiful supplies of food,

our medicine and sanitation, almost everyone,

irrespective of their genetic make-up, can survive long enough to pass on their genes.

So can we really still be evolving today?

I've come to a place where there are clues about our current evolution.

And I'm going to meet someone who believes that on these tombstones,

there's evidence that natural selection itself might be dead.

This is a good place to remind ourselves, the patterns of life and death,

which are the raw material for Darwin's great engine of evolution,

natural selection, they've changed dramatically in the 21st century

compared to the 20th and in the 20th century compared to the last

10,000 years and to me, that says that natural selection at least,

if it hasn't stopped, has at least slowed down.

Most of these graves are 19th century, a bit before,

and here's one, it's an absolute classic from the 1870s.

Somebody died in their 40s, then if you go down,

-there's young Robert died aged three months, then another one.

-And another one, yeah.

So lots and lots of childhood death. And that's true on nearly all these graves.

As you come through, you see dead babies under these gravestones.

Steve there's another one here,

this is another tiny baby died five months, four years and five months.

Four years and five months. These are individual tragedies

but they also tell us something important about biology and the figures are quite amazing.

In Shakespeare's time, about one English baby in three made it to be 21.

In the year of Darwin's birth, about one English baby in two

-made it to be 21.

-It's a real lottery.

But now, about 99% of the English babies born make it to be 21.

It's a nasty thing to say, maybe, but these dead children,

these were the fuel, the raw material of natural selection,

many of those kids died because of the genes they carried.

Well, certainly just personally, I'm asthmatic and

I would've probably died as a child,

so I wouldn't have been able to pass my genes on

had it not been for the modern drugs which got me through.

I think the real reason that evolution has come to an end

is partly modern medicine but more important perhaps, modern engineering.

It's worth remembering that even in the year of The Origin of Species

that the House of Commons had to put rags in its windows, soaked in bleach

because of the stench of the filthy water in the Thames.

People died of cholera in their millions, that's all gone.

Do you think there's a danger that we're being a little arrogant

and short sighted in thinking that we have removed ourselves from natural selection,

because when the next really big disaster comes along, it'll be back.

That's probably true. We don't know what that disaster will be,

but there are all kinds of horrible things just lurking around the corner.

The one which is really worrying is epidemic disease.

There are so many people who travel around so much,

that it's certainly possible that something like the black death or cholera could come back.

It's clear that our lives have been transformed in the last couple of centuries,

that medicine and engineering now mean that we are much safer,

that an individual is much more likely to survive to adulthood

and at least get the chance to pass their genes on.

So this really could be as far as we'll go...

the technological developments of the last century

might have brought us to the end of the evolutionary line.

But for that to be the case,

we'd need to keep in control of disease, forever.

All it would take for natural selection to make a comeback in the developed world

would be a lethal, contagious disease.

We may be in control for the time being,

but viruses and bacteria don't stay the same,

they evolve too.

So our future is inextricably linked to what happens to them.

Professor Andrew Read has been studying a deadly virus.

It affects chickens, not humans,

but it has worrying implications for our future.

So with this virus now, every time a bird gets infected, it's fatal?

As far as we know, yes. This is on a liver,

this is the liver of a chicken here and you can see these are tumours,

cancer tumours that have been caused by the virus and obviously

four or five gross tumours on a liver like that...

It's just shocking.

The virus is of particular concern because it wasn't always this virulent.

Something that humans have done has caused it to evolve.

The original virus did not cause anything like this.

The strains that we now have

circulating in farms today, they do this sort of damage.

The virus itself has changed

and become much more damaging to the birds.

What did we do to make it go from something that was just

a minor irritant to something that kills all chickens in ten days?

Unless we can work out what we've done to cause the virus to evolve

in such a lethal direction,

we could be at risk of doing the same thing to pathogens that affect humans.

So I suppose the thing to realise is that we're not alone.

We tend to imagine that evolution is us against the environment,

but there's a lot of ongoing arms races between

different species as they evolve and change the world and each other.

In their laboratories, Andrew and his team are trying to understand

what made the virus evolve,

to see what it can tell us about our own future.

What can these chickens tell us about diseases in human populations?

I think one of the lessons of the poultry industry has been that

when you change things radically, the diseases that are in them

often change radically as well.

It's very hard to imagine that the cause of this evolution

was not something to do with the intensification and

the commercialisation of the chicken industry.

And Andrew has a surprising theory about why the virus

evolved in such a dangerous way.

The most popular hypothesis, and the one that most of

the work is going on and what we're interested in, is the possibility

that vaccinating the chickens against the virus has done this.

That vaccinating the chickens has actually caused the virus to change?

Yes. If you keep the birds alive with vaccines, that allows

a much longer transmission period, it keeps the birds going much longer,

so the virus, although it's very hot,

is not killing the bird any more because the vaccine's stopping that.

So, that allows it to transmit

in a way that it wouldn't have done in a pre-vaccine era.

I think this is really interesting, cos it shows quite clearly

that we can assume that

we're somehow removing ourselves from natural selection by using medicine

to deal with disease, but actually what we're doing

is just changing the, kind of... the selective landscape out there.

Yeah, as a disease evolutionary biologist,

I don't feel like I'm about to go out of work.

Things are always changing.

Just take drug resistance.

Bacteria that we thought we had under control, lots of them now

are becoming multi drug resistant. There are some bacteria now that

can't be killed by drugs, known drugs, that wouldn't also kill us.

But the virus' evolution might also be due to modern factory farming,

with vast numbers of chickens packed in closely together.

It's a change in the chickens' habitats

that mirrors our own increasingly urbanised world.

So do you think that pathogens like viruses and bacteria

will always be there in our environment, shaping our evolution?

They're always going to be there. How they shape human evolution

is going to be very interesting.

There's not going to be a day when we declare the war

on infectious disease over. That is not going to happen.

With the work of people like Andrew,

we may be able to at least keep on top of infectious disease for a while.

But it's hard to imagine that we'll always be in control.

It seems that some diseases are evolving just as rapidly

as we're devising weapons to combat them.

And that means that there is a possibility that at some point in the future,

a particularly nasty infection could take hold and

even turn into a worldwide pandemic that decimated populations

not just in the developing world, but in the developed world as well.

And that would put natural selection back into the driving seat.

But perhaps it isn't just about death and disease.

Perhaps what matters more, is birth.

After all, even if these days almost all of us survive

long enough to have children, some people have none,

some people have three or four.

And that difference must drive evolution, in the same way as if

some people died before being able to pass on their genes.

So, if we can work out who's having the children in our societies,

perhaps we can guess what future generations will look like.

I've come to a small town in Massachusetts, called Framingham.

On the surface, there's nothing unusual about its inhabitants.

But actually, it's the first town in the world where the future evolution

of the people living here hasn't just been guessed at,

it's been calculated.

And Stephen Stearns is the man who's calculated it.

-So this is Framingham - this is where you've been doing your research?

-This is Framingham. Yes.

Your work is ground breaking because you're looking at human evolution

from the perspective of investigating fertility patterns.

That's right, and we've been able to discover some really fascinating things with it

and I think the key thing here is that we've been able to use these fertility patterns

to see that evolution is still going on in this town of Framingham and

that it is changing, er, traits such as height and weight, age at first birth,

age at menopause, and this was unexpected. This was quite exciting.

Steve chose Framingham for his study because he had access

to unprecedented levels of data about local residents,

spanning 60 years.

And by examining how many children tall people have,

or blonde people have, or brown-eyed people have,

Steve has been able to work out what the next generation might look like.

It's an entirely new approach to the study of evolution.

Well, it's interesting, if one goes back and looks at the way that

Darwin formulated natural selection.

Darwin thought mostly about mortality,

and it wasn't until some time in the mid to late 20th century

that people really realised that it's not really mortality,

it's reproductive success that is what's changing gene frequencies.

So given what you've already measured, can you be specific about

the changes in height and weight that you might expect to see in the future?

What we have found with height and weight, basically, is that natural selection

appears to be operating to reduce the height

and to slightly increase their weight.

So people are getting shorter and fatter?

They're becoming more pleasingly plump.

And do you think this is something which is...

Is this a real biological change?

Is it a genetic change, or are we just looking

at a cultural influence?

Are people just eating more?

Well, there's no doubt that there are big cultural effects on things

like weight.

But we can estimate what the genetic component is of the variation in height or the variation in weight.

So we're pulling out a small genetic signal,

and a fairly small selection pressure.

And if this were to act consistently, it would add up to major change.

It isn't the evolutionary future that many of us would've expected.

But there it is.

Shorter and fatter.

But perhaps we won't be heading in that direction forever.

I think what's very probably going on is that selection is

moving a population up and down all the time. It goes off in a certain direction for a while

and then it goes back in the other direction.

It's only if you get a significant change in the environment

that it will then continuously go in a new direction.

Can you predict anything else about how we might evolve in the future?

Are there any other traits that we might see coming to the fore?

In the long term, I think that where we are going at this point

is actually absolutely unknown.

We see rapid evolution when there's rapid environmental change

and the biggest part of our environment is culture and culture is exploding.

That's, I really think, the take-home message of the Framingham study,

that we are continuing to evolve, that biology is going to change

with the culture and it's just a matter of not being able to see it

because we're stuck right in the middle of the process right now.

It seems that far from being over, our evolution is impossible to stop,

and the enormous changes in the way we live over the last century

may be driving it even faster than ever.

And now, human evolution

is on the brink of taking an entirely new turn.

We could be about to rewrite the very rules of natural selection.

We've reached a point now, where our technology could affect

our evolution in a way that seemed unthinkable just a few decades ago.

We're on the verge of being able to literally write

our own genetic future.

I've come to Los Angeles,

a city whose inhabitants are determined to have the perfect body.

Whether through exercise, surgery, or other means,

the goal is nothing less than physical perfection.

And with genetic engineering on the horizon,

that goal could be one step closer.

I'm about to meet somebody who's had more of a hand in shaping the future

of humanity than almost anybody else. Just last year,

he was instrumental in the creation of around 400 new babies.

Dr Jeff Steinberg was involved in creating the world's first test-tube baby back in 1978.

At his clinic in LA, he's still helping people to conceive.

So are these all pictures of test-tube babies?

They sure are. They sure are. Some of the thousands.

But nowadays, he's helping couples create their very own designer babies.

His clinic routinely screens embryos for genetic diseases,

and more controversially, it was the first in the world to offer people

the choice of cosmetic traits.

Selecting offspring like this could change the course of our evolution.

And it all starts with something that still utterly amazes me -

the very beginnings of human life. A living embryo.

So we'll come over here and this will give us a great chance

to actually watch the biopsy of the embryo.

So this is when you take the cell to look at the genetics.

Yeah. So to do that, we've got to separate the one cell

from the other eight cells inside the embryo.

And you can do that? You can take a cell away

and the embryo will still carry on developing normally?

Totally normally. It's like it never happened.

So you can see the multiple cells on the embryo.

So at the moment, it's a ball of about eight cells?

An eight cell embryo. We've applied the suction pipette to it so it'll hold it in place for us,

and now we're going to pierce the zona pelluca -

the outer shell that protects the embryos -

and we're actually going to prepare to go in and remove

one of the cells so that we can analyse it genetically.

-That single cell, it's there.

-It's out.

And you can see the remainder of the embryo's not phased a bit by that.

So then you're able to look at the genes contained within that cell,

which are identical to all the other ones?

-Yea, yeah.

-And analyse it and look at the, look at the genes that you've got there

-and screen it?

-That's exactly right.

By screening a cell from each embryo, Dr Steinberg can work out

which embryos are free from genetic diseases.

But he can also screen the embryo for other traits.

-So you're also picking up the sex of the embryo.

-Yes.

Are you actually allowing people to choose whether they have a boy or a girl?

Anyone can choose here. Yep. They can choose a boy, choose a girl,

and we've done this close to 9,000 times now.

It just seems so peculiar. It's such an odd thing to do,

-to be able to determine the sex of your baby.

-If a couple has five girls,

they're going to walk in and say, "We want a boy."

OK, so what about other traits?

Not the sex of the embryo, not things which are potentially going to cause a disease,

but other things, like eye colour or hair colour?

We actually isolated the genes that allow us to choose eye colour and hair colour in the Scandinavians.

Right? We announced it, and we started hearing from

people that were interested in this, but we also heard from a lot of people on the outside,

including the Catholic Church,

that had some big problems with it.

And they said, "No, not at this point."

So we retracted it. Even though we can do it, we're not doing it.

So the technology is available right now to basically have a designer baby, where you choose the sex,

choose the eye colour, choose the hair colour,

-choose how intelligent they are?

-In our life times, I think we will see

tremendous advances made in determining where intelligence comes from,

identifying the genes that are associated with intelligence,

and perhaps maybe not being able to guarantee an intelligent person,

but certainly guarantee that we will contain the chromosomes

that lead to the ability to develop better intelligence.

Do you think this is a good idea?

I'm not sure if it's a good idea and that's why we're not forcefully pursuing it right now,

and we're going to need help from the outside world.

We need help from the ethicists, we need help from the geneticists

and we need help from society.

However, if you want to know what the future holds,

this is where the future is taking place right now.

It seems to me that this really is a watershed moment

in the future of humanity and in human evolution because we're just on

the verge of actually being able to genetically engineer our own future.

I mean, this is something which evolution on this planet

has never experienced before -

a species actually taking control like this.

I think it will play a huge part in our evolution and I think rightfully so.

We need to be cautious about it because it can go right and wrong.

But I think it's going to get better, it's going to get more beneficial

and it's going to help more people.

But I think trying to remove it as part of our future evolution

is just a task that's not going to be accomplished.

It's here. It's not going away.

The technological and ethical problems

with genetic engineering may be vast,

but our ability to manipulate our genomes

is likely to have a profound effect on our future evolution.

We're about to turn the page of a new chapter

in the history of our species.

It's clear that we'll never stop evolving.

But how we evolve depends on how the world changes,

and how we change the world.

And right now, the world we live in has never changed more quickly.

And that means we might be evolving faster than ever.

Who knows where it might take us?

But there is something about our future that is inevitable.

In the long term, the world around us

will change dramatically, and when that happens, there are two possibilities.

We'll either evolve, and evolve in a big way, or die.

So humans as we know ourselves today will no longer exist.

Humans are pretty special, but they're not that special.

99.9% of all animals have gone extinct and I'm pretty sure

we'll go extinct in the end as well.

A global catastrophe could wipe us all out.

But if some people managed to survive and adapt to whatever new world they lived in,

they would continue our evolutionary journey -

a journey that began 3.5 billion years ago.

I think we'll become extinct as we know ourselves now,

but I think we've already done that several times in the past.

If we are to compare ourselves to the cavemen, we're not the same animal.

In the broadest possible sense, we haven't always been human,

and we won't always be in the future.

We are neither the pinnacle of evolution,

nor its endpoint. We're just part of the journey of life on Earth,

and evolution will continue as long as the planet can support life.

Our species is just a tiny twig on this massive tree of life,

and it's a twig that's still growing,

still changing, and I don't think it's about to be pruned just yet.

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