Translator: Michele Gianella Reviewer: Chiara Polesinanti
Evolution is possibly the field of science
that tells the most stories.
It tells a lot of stories,
but unlike the myths and tales we tell children
we try to reconstruct them using evidence, facts and signs.
A bit like Sherlock Holmes.
But stories, we know, are slippery: they have pros and cons.
They can fascinate us, but they can also deceive us.
They may present us with false reconstructions.
Many years ago, a colleague of mine, far more illustrious than me --
his name was J.B.S. Haldane,
and he was one of the fathers of population genetics --
was in a very formal salon in Oxford
in the presence of theologians, ladies and princesses.
And one of the ladies asked him,
"Excuse me, Professor Haldane,
but if you were to imagine the Creator,
how would you see him? How do you picture him?"
It was a somewhat loaded question
because Haldane was known to be an atheist, a disbeliever, a communist.
He was a bit of an oddball, especially in England in those days.
And Haldane replied,
"Look, ma'am, I don't know.
But if I were to imagine the Creator,
I think he has
an inordinate passion for beetles."
What did Haldane mean?
He meant that if we look at the earth and biodiversity
from an evolutionist's point of view,
the first thing we notice
is that we are at the edge of the empire,
we are not at the centre of this story.
We are one of the many wonderful species created by natural history.
The story I'm about to tell you is the result of very recent research.
So let me tell you what we discovered but a few months ago
and decisively disrupted our way of telling the story of human evolution.
Basically, it is the story of a disappointment,
but a constructive disappointment, a disappointment that is good for us,
that makes us think,
that once more sets in motion
the great questions that science is able to raise.
Where do we come from? Why? What are we doing here?
What is the place of man in nature?
The beginning of the story is in this image that you see behind me.
It is a fascinating, mysterious page written by Charles Darwin himself,
dating back to July 1837.
If you remember the dates, it means he was very young.
He was born in 1809, he was not yet thirty.
He had just returned
from a wonderful five-year voyage around the world, which we've all studied.
He came back in 1836 and, as soon as he got back,
he began writing in these private notebooks.
Very private.
So secret that they were to practically become
the only Darwinian writing that he decided never to publish.
He is known to have said,
"I entreat you never to circulate
what I wrote as a boy just back from my voyage."
On one of these pages,
there is this beautiful diagram that he called The Tree of Life.
And he wrote, see, "I think…",
because, for the first time, he was writing to himself,
he was talking to himself about what he'd understood about evolution.
That is, evolution is a tree
and like a tree it has a trunk, so common ancestors,
and then it has ramifications,
species that diversify over time
and then become extinct, that multiply and so on.
An interesting story, a plural story, made up of many different species.
Why am I telling you a story that is actually a disappointment?
It is because when we applied this Darwinian idea --
already back in 1837, then he became famous,
and 20 years later he published "On the Origin of Species" --
when we dealed with human evolution,
scientists themselves actually made an exception.
And I say scientists themselves, not lay people or opponents of evolution.
And if you look at how Thomas Henry Huxley reconstructed human evolution,
you'll see that it's very different from the tree I showed you before.
The first was a story of diversity, of multiplicity,
of coexistence of different species.
This is a very different story,
where there's only one species at a time, we proceed in a linear fashion.
This is a great story of progress.
It's what a colleague of mine,
who was very important in my training,
his name was Stephen Jay Gould,
called "our great illusion".
The illusion that Homo Sapiens,
who is always placed at the end, at the far right,
should represent the culmination of evolution.
The illusion that the Story should necessarily lead to us.
Surely this image is very familiar to all of us.
We always come across it, in newspapers, on television,
we have seen it many a time.
What we have recently discovered is that this exception is not valid.
It's been proved wrong, we've called it into question.
Human evolution did not take place that way.
I'll show you other alternatives to this image
that is used in advertising, it is used everywhere.
My favourite one is that one at the top right corner.
It appeared in a feminist magazine
and it compares the slow and gradual but progressive evolution of the male
with that of the female, very stable actually.
I've found all sorts of variants of this image.
It's a sort of major icon.
An iconography.
Even today, when we publish articles on human evolution in newspapers
they always illustrate it with this image.
It also happened to me recently.
The first line of my article was, "There are no missing links in evolution."
And they accompanied it with this image showing the missing links of evolution.
So it's something very powerful, deeply rooted in our minds.
The version that I definitely choose as the absolute best in the world
is this one that was proposed in The Simpsons
where evolution culminates inexorably and wonderfully in Homersapiens,
whom you see at the far right.
Why is this exception very strange?
Because while we kept on upholding this great iconography of hope,
scientists forged ahead
and rewrote the evolutionary stories, the natural stories of the species
in a very different way.
This image is less easy to understand than the previous ones
but it is wonderful.
Let me tell you one thing:
I think that if an alien were to fall to Earth
and we were to tell him
about one of the great achievements of science and knowledge --
yes, true, we have the theory of relativity
and a lot of discoveries in the field of physics
but I'd show him this picture,
and say "Thanks to science,
the species Homo sapiens has managed to do one thing:
it's managed to assemble and reconstruct the Tree of Life,
that is, to decode kinship across all living beings,
but really all of them, from bacteria up to the most complex animal,
up to the jaguar, the giraffe, to the humans
who have inhabited and do inhabit now this planet.
This Tree of Life brings together all the living beings we know."
And you see that it is a tree,
it has many branches, there are many species.
If you want to find yourself, it is extremely complicated
because we're here, the animals in here,
and we happen to be closer related to mushrooms than to plants,
another thing we don't really like.
And among animals
you have to go from twig to twig to twig for nine times
before you find Homo sapiens.
In other words, we're at the edge of the biodiversity empire
as Haldane said with that funny quip when he wanted to shock the lady.
The same thing holds true if we approach our personal history,
that of our family: we find the same pattern, can you see?
I don't want to go into this because it is a bit too technical,
but if you look at this image we are here, we are this species,
we are in this genus, the genus Homo.
If you look back, you find a story of major ramifications like these.
What you find is a bush, not a ladder.
You don't find linearity, you find multiplicity.
And interestingly, if you look at such schemes
and you draw any time line --
imagine you have a time machine,
choose any epoch, 10 million years ago, for example,
and draw the line --
you will discover that at any time of evolutionary history
there were many different species existing at the same time,
more or less related to one another.
Here you see that if you start from today,
Homo Sapiens shares a common ancestor with chimpanzees
who lived some 6/7 million years ago,
and going further back he shares one with gorillas,
with orangutans, gibbons and with all the other living beings,
so this is a very synthetic, very powerful image.
Why was this powerful image of evolution called into question?
As is often the case in science, there's a bit of inertia,
new ideas sometimes have a hard time to be accepted,
then one is submerged by anomalies.
That model didn't work and in the end, though reluctantly, we abandoned it.
This is a beautiful discovery made in 2009,
and it is so important that Science devoted no less than two covers to it.
So, the most important discovery of 2009 is our possible ancestor called Ardi,
from Ardipithecus.
If you look closely at it,
you can see that it has a mix of modern and archaic features.
It is a bit ape-like as you can see from its very long upper limbs
and its divergent big toe,
yet it is perfectly bipedal, with a flat face
and therefore presents a mix of characters.
Now, interestingly, we discovered
that our ancestor wasn't to be placed
at the beginning of the evolutionary process
but lived at the same time as others.
Look, this is pretty incredible.
This is a valley in Ethiopia, a single valley in Ethiopia.
We Sapiens also originated in that area, in one of those valleys.
In just one of these valleys
there were no less than three different human genera,
here shown in different colours,
and none of them happened to disappear or be replaced by another one.
They simply lived together in a bushy way.
Some died out, some new species appeared
and that complicated and interesting image of evolution,
which concerns us directly, was created.
So this is how my colleagues and I rebuilt human evolution.
See, time flows from bottom to top.
It's a real bush.
You see that from the days of our common ancestor with chimpanzees
there have been about 20, maybe even 22, some even say 25 different species.
That's anything but a linear evolution.
It's a lot more complicated,
there's loads of different species.
Even here, wherever you draw a line, you find a lot of species coexisting.
What we have recently found out, in the last year and a half,
and what actually shocked us as we hadn't been expecting it,
is that this is true even in very recent times.
If you look here,
Homo sapiens is at the top right and we are the last twig, this one.
This is the present.
If you just go a little back in time, even only 40/50,000 years,
you discover that there were other human species on Earth.
And we have recently found out
that up to 30, 35, 40,000 years ago at most, mind you,
five human species coexisted on Earth, at the same time.
That's something we hardly figure out: five different human species!
If an alien had fallen to Earth 40,000 years ago,
he would have seen us Sapiens
roam around with four other human forms.
This, of course, opens up many important and intriguing questions.
This is one of the latest discoveries,
made in Indonesia on a small island called Flores.
We found storks 1.80 m tall,
mice 1.50 m long, tail included,
and small Hominini, which hardly ever exceeded 1 m in height.
This is a relative of ours, a cousin of ours,
discovered a few years ago on this island
where it had been stuck for hundreds of thousands of years,
and had become very short.
This is an evolutionary mechanism called insular dwarfism and it often occurs.
It also occurred in Italy.
As you may know, dwarf elephants lived in Sicily,
they were as big as a large dog.
Dwarf mammoths lived in Sardinia.
This is because when large warm-blooded species get stuck on islands,
it is better for them to become smaller, in terms of natural selection.
But incredibly, this is the first time
that we see this occurring in a human species.
But even more shockingly,
so much so that it took us a few years before we actually accepted the fact,
this specimen here,
immediately called Hobbit Man, by scientists,
that Hobbit Man on that island, Flores,
carried on and survived until 12,000 years ago,
the day before yesterday.
At school, almost all of us studied the Egyptians, the Sumerians,
the civilizations who invented writing, the pyramids.
Take the pyramids, go back a few thousand years
and on Earth there was another human species, related to us,
with whom we coexisted
and whom we also met as we actually visited that island.
We know that because Homo Sapiens
went in Australia long before their extinction.
And we also know that we met, we saw each other.
But there have been even more shocking close encounters of the prehistoric type.
This is the latest discovery; the paper is from April 2010.
In short, in a cave in the Altai mountains in southern Siberia, on Asia,
we identified another human species whose existence we had had no inkling of.
We knew that this cave, the Denisova cave, had already been inhabited by two species:
we the Sapiens, already 40/50,000 years ago,
and the famous Neanderthals, we've all studied about at school.
You know that Neanderthal was not an ancestor of ours,
he was a cousin of ours.
We coexisted with him:
even here in Italy, in these valleys, in these areas
there were villages inhabited by Sapiens and others by Neanderthals.
We probably communicated, maybe we even swapped technologies.
There are sites where sometimes an innovation,
which had already appeared in a Sapiens settlement,
was then found in a Neanderthal one and vice versa.
This shows that there was an interaction.
Our evolutionary history is checkered with alter egos.
We have never been alone.
We've been alone on this planet for a very short time indeed.
And in that cave, scientists expected to find remains
of either Sapiens or Neanderthals or possibly both of them.
They took a little finger, a phalanx, from a skeleton,
brought it back to Germany and extracted its DNA.
That can be done today: we don't live in Jurassic Park, but it can be done!
You extract the DNA and see which species it belongs to.
It turned out it belonged to neither Sapiens nor Neanderthal
but to yet another species.
So a very complex history of coexistence.
You must be wondering about something that we are all curious about,
because evolution, Gould said it himself, is a story of death and sex
and we're always very interested in both.
Well, we don't know what caused these species to disappear, to die out.
They all became extinct very recently,
and I know that you suspect we might have had something to do with this.
We probably did play a role in their extinction,
but we don't know exactly how, as nothing dramatic happened.
We can state for sure, it was not a genocide.
We did not kill them off directly.
Something else must have happened that led to their progressive regression.
The fact is that, recently,
we became the only human species left on the planet.
Then there is the sex side and this is also surprising.
Up to a few months ago
I would have told you that different species could not interbreed.
We thought there was a genetic barrier.
But the last discovery we made proved that this was not the case.
Actually, all non-African Sapiens,
that is those who came out of Africa and remained out of Africa,
probably have a 4 to 6% proportion of Neanderthal traces in their blood.
So we carry some traces of Neanderthal DNA in our blood.
How is that possible?
The only explanation, or at any rate, the most plausible explanation
is that at least at some time in the past, possibly in the Middle East for some,
for 10/15 thousand years we may have mated.
We had fertile matings, so the two species interbred for a while,
then they separated, one of them died out and we Sapiens had the upper hand.
But this is a dogma that is refuted because our genome is not only ours,
so we must not be too jealous.
It is a cloak of Harlequin
in which there are traces of other species.
We are not alone, not even in our genome.
I'm now showing you this image because we came out of here.
This is another very recent fact: the strait of Djibouti.
Populations of the Sapiens crossed this small passage,
and then met the other species that had left earlier:
the Neanderthals, the Denisovans I have just shown you,
and then the Indonesian species.
This is a summary of everything I have told you:
we ventured out of Africa,
we did so repeatedly from 100/120,000 years ago
and when we came out, we met other existing living forms,
human species related to us.
We coexisted, we sometimes mated and then we colonized the whole world.
We're the only one, for example,
who arrived in Australia and then colonized the Americas,
because in the ice ages the world was different
from what it appears to be like here.
There were entire continents that are now submerged, like Beringia,
or this whole area which was passable.
So you could get there without crossing the sea
from South Africa to South America.
One of the consequences, of course, of this whole story
is, first, that perhaps
we need to look at evolution with a little more humility,
without thinking of ourselves as the ultimate end,
especially since we interbred.
And interestingly,
but I'm saying it only now, in closing, because I didn't want to shock anyone,
we also know that the interbreeding was asymmetrical.
It was always a Neanderthal male with a Sapiens female.
That for us Sapiens boys is really disheartening
(Laughter)
because we had our females stolen from us 40,000 years ago already,
so evolution punched us in the stomach.
But the second consequence is more serious:
if this is our history,
then what we have always called "human races" do not actually exist.
We are a young species,
we all come from a very small group
and there was no time to separate human races.
So let's delete the concept of human race from the language of science.
Thank you!
(Applause)