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So we're shifting gears today.
We're going to talk about molecular

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evolution, i.e. how do
we understand how species

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evolve, how do we understand
a lot about ourselves,

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how human evolution is taking
place over the last couple hundred

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thousand years.
And traditionally,

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evolution has been the purview of
people who study the morphology of

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organisms, and when I talk about
morphology, obviously I'm talking

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about shape and form. And
by comparing organisms,

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starting already 250 years ago,
one began to develop hierarchies of

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how different organisms on the
planet are related to one another.

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You've seen this, undoubtedly,
in high school biology.

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This is the study of phylogeny,
and phylogeny has traditionally been

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figured out by comparing the
phenotypes, the morphologies of

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adults, sometimes embryonic
development, and on that basis,

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attempting to extrapolate
back in evolutionary time,

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about the relatedness of different
organisms, one to the other.

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And in so doing, one
has been able to create,

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for example, family trees, here's
something that Charles Darwin was

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already interested in, the
various kinds of finches on the

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Galapagos Islands off Peru, in
the Pacific. And here, one is

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beginning to organize different
bird species on the basis of whether

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they're more closely or less
closely related to one another,

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and to draw pedigrees, which,
one imagines, describe how they

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evolved, one from the other.
i.e., organisms which are very

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similar to one another must be
more closely related evolutionarily,

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and conversely, those that appear
very differently from one another,

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morphologically, must be far more
distantly related to one another.

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In fact, these kinds of morphologic
extrapolations can be very

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misleading. So here, for
example, are two kinds of eyes.

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The top eye is
a Drysophila eye

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which, to state the obvious, looks
a lot different from our eyes,

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which is that the chordate
eyes shown the bottom.

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Totally different. Our rods
and cones face backwards,

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the Drysophila Arthropod eyes,
the light sensors face forward.

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Everything is different.
And on the basis of that,

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you would say that these
two organisms are independent

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evolutionary inventions, that
they've been invented on two

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occasions, and that they have
no relatedness, one to the

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other, at all. But I will
tell you an extraordinary

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experiment. You can take, there's
a master gene that controls

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eye development in the fly,
Drosophila. It's called eyeless,

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if you knock it out then the
eye doesn't develop at all.

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And you can take out of the mouse,
what is apparently a related gene

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called small eye, so the
fly gene is called eyeless

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and the mouse gene is called small
eye. And you can put the small-eyed

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gene into the Drosophila genome, in
a fly that lacks the eyeless gene.

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So here we're
talking about two

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different genes. The fly
gene is called eyeless,

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the mammalian gene, at least
in mouse, is called small eye.

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If you knock out this gene in the
fly genome, and replace it with this

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gene, you get a perfectly
normal Drosophila eye.

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It's extraordinary. Or
you can do the following,

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you can arrange it so that the
mouse small eye gene is expressed

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ectopically. When
I say ectopically,

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I mean that it's expressed in the
wrong place, at the wrong time.

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So you can do the following
experiment. In a fly genome,

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you can arrange it so that the mouse
small eye gene becomes expressed on

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one of the extremities of the fly,
on one of the legs of the fly. And

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now, on one of the extremities of
the fly, an ectopic eye will develop,

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looks just like a Drosophila eye,
but it's development is programmed

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by the mouse small eye gene.
What I'm telling you is that these

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two genes are totally interchangeable,

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that they are effectively
indistinguishable from one another,

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functionally they have some sequence
relatedness, but in terms of the way

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they program development, they
are effectively equivalent.

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And what this means is that the
progenitor of these two genes

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must've already existed at the
time that the flies and we diverged,

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which six or seven-hundred million
years ago, and in the intervening

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six or seven-hundred million
years, these genes have been totally

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unchanged. i.e., once
the gene was developed,

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evolution could not tinker with it,
and begin to change it in different

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ways, ostensibly because such
tinkering would render these genes

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dysfunctional, and thereby
would inactivate them,

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thereby depriving the organism
of a critical sensory organ.

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So here we have an example,
a dramatic example, of how

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morphology misleads us. Here
we have an example of where we

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would say these two eyes, the
two eyes I've shown you here,

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are so different from one
another that they must,

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by necessity, be independent
evolutionary inventions.

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But in fact, genetics tells us,
and these gene-swapping experiments,

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tell us that the two eyes descend
from a common ancestral eye,

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a prototypical eye, whose precise
morphology we can't discern anymore.

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And so we begin to realize that
if we really want to understand

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evolution and we really
want to understand phylogeny,

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phylogeny being how the species
are related to one another,

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we have to the DNA, and we have
to begin to look not at phenotype,

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but we have to look
instead, at genotype.

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The Darwinian model is pretty
much like this, the survival of the

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fittest. And when I say that,
we imagine that we have here, a

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genetically heterogeneous group
of organisms within a species,

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and this, this number of individuals
in the species could be 100,

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it could be 1,000,000.
This particular individual,

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by chance, acquires a mutation,
or an advantageous allele, through

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some genetic alteration. This
genotype renders this organism

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more fit, phenotypically,
has a selective advantage and

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consequently, over extended periods
of time, which may be thousands or

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even millions of years, the
descendents of the organism

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bearing this allele now have
advantage, have greater reproductive

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advantage, survival advantage,
compared with the other individuals

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in the same species, and
therefore, the representation of

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this mutant allele in the gene pool
of the species becomes expanded.

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When I say gene pool, I'm
talking bout the common shared

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set of genes within the species,
such as within the human species.

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And so eventually, the
descendents of this organism,

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or the descendants of an
organism bearing this allele,

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now become overrepresented in the
population, because they're more fit.

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And then there can be
another succession, i.

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., there could be other
mutations occurring subsequently.

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Once again, favoring the selective
outgrowth of an individual bearing

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this allele, or this
allele. And in addition,

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there can be the process of
what one calls, speciation.

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That is to say, that if some parts
of the species live in one place,

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and other parts of the
species live in another place,

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geographically, they may no longer
interbreed, and as a consequence,

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and because of the fact they're
under different selective pressures,

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they may begin to diverge from
another if, evolutionary speaking,

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because they're no longer actively
exchanging genes within one another.

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And, as a consequence, one
can have new species arriving.

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And what one believes,
this happens over slow,

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slowly over evolutionary time, but
it does arise, and to the extent

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it does, one eventually ends
up with organisms here and here,

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which can no longer effectively
interbreed with one another.

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That is to say, they become
genetically so different from one

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another, that any hybrids
formed between them are,

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in fact, sterile, for one reason
or another, if they're at all

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interested in breeding with
one another to begin with.

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And what this means is that we
can begin to trace how closely or

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distantly related species are to
one another, simply by asking how

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closely or similarly related
are their DNA sequences?

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If, distantly related organisms
have very distantly related

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sequences, and closely related
organisms must have sequences which

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are very similar to one another.
And over evolutionary time, there's

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a so-called mutational clock,
where one, where each species

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accumulates a certain
number of point mutations,

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base substitutions in it's DNA,
per million years, and the longer

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the two species are separated from
one another, the greater will be the

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difference in their
sequence diversity.

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And on that simple basis,
one can begin to construct

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evolutionary trees of, for
example, the entire cellular

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life on the planet. And
here's such an evolutionary

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tree, where what's being compared
is the ribosomal RNA sequences,

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i.e., the small ribosomal RNA.
Remember, ribosomes have two

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subunits, small and large,
in the case of prokaryotes,

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it's 16S RNA, that is,
it's sedimentation rate.

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In the case of mammals,
it's 18S. In both cases,

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these are small ribosomal RNA
subunits. The ribosome was only

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invented on one occasion during
the evolution of life on the planet,

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so one can begin to compare since
all cellular life forms have life

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forms, one can ask how similar,
or dissimilar, are the various

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sequences and coding, in
small ribosomal RNA subunits?

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And on the basis of that, one has
concluded that there are actually

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three branches of cellular
life on the planet.

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The bacteria indicated here,
this is not such a great Xerox,

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where you see a whole series
of different kinds of bacteria,

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indicated on this tree. Sorry
about the poor reproduction.

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Here there's a dashed line
indicating that we're talking,

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there's a second kingdom in the
middle here, indicated by what are

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called archae, and
the archae are also,

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from our point of view, prokaryotes,
but they're not bacteria. They are

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a single-cell life form,
they're often found in unusual

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situations, for instance, in
thermal vents in the bottom of

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the ocean floor, some of
them are able to stand high

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salt, some of them are able
to stand high temperature,

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like therma fillus, therma
proteus, and so fourth.

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And these, their ribosomal RNAs,
are so different from those of

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bacteria, that they've been placed
in their own separate kingdom.

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And finally, here are the
eukaryotes, all over here.

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These are all eukaryotic cells,
starting here. And we, our cells,

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seem to be slightly more closely
related to those of the Archaea,

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if you follow this ribosomal
sequences, than they are to

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the actual bacteria. So,
there's actually two major

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prokaryotic life forms on the
planet. The first living organism,

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well if you begin to try to
look back in geological record,

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it looks like the first living
cellular life forms existed already

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3-3.5 billion years ago, not
so long after the planet was

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formed, which was between 4.
and 4.5 billion years ago. And

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here's the whole eukaryotic tree,
and if we look at the eukaryotic

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trees, remembering here that we're
starting at 3.5 billion years ago,

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And we're using this evolutionary
clock to determine relatedness,

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then we see a whole series
of single-cell eukaryotes,

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here are their names are,
these are protozoan, eukaryotic

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protozoan. Here's Amoeba,
here are slime molds, here are

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cilliates, we're still
at single-cell organisms.

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Finally we get to
multi-cellular organisms, plants,

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fungi, and animals, and so,
all animals on the planet

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are a relatively recent invention.
All animals, all of the metazoan,

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are just on this very small branch,
and we know that this very small

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branch started around
600-650 million years ago,

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maybe 700 million years ago.
And that was the time, roughly

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speaking, when we and flies
last had our common ancestor,

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otherwise, to state the obvious,
we and flies are very different.

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The fact that the gene for
encoding the eye has been conserved,

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so faithfully, over enormous
evolutionary period of time

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indicates something else,
And that is, certain genes can

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evolve progressively over
a long period of time,

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because they don't encode vital
functions, or they may even be

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sequences between genes that
don't encode phenotype at all.

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Imagine, for example, we have a
situation were here we have a gene

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which encodes a vital function,
like the eye, here's another gene

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that encodes another function,
oh I don't know, a leg.

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And here we have intergenic
sequences. After all,

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as you have learned by now,
more than 96% of the DNA in our

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genome, doesn't encode proteins,
and probably isn't even responsible

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for regulating genes. So
these sequences, right in here,

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can mutate freely during the course
of evolution, without having a

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deleterious effect on the
phenotype of the organism.

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There's no evolutionary pressure
to constrain the evolution of these

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genes, but if this gene
over here encodes an eyes,

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And if this gene has been
optimized in it's sequence,

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early in the course of evolution,
that any subsequently occurring

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mutations will compromise it's
function, and therefore there's

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enormous selective pressure to
eliminate any organism which has

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begun to tinker with the sequence of
this gene, by changing it's sequence.

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Here, in stark contrast, there's
no such selective pressure.

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The organism,
that is,

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can tinker at will with this.
I don't mean literally that the

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organism is able to tinker
with it's own DNA sequences,

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but the hand of evolution can
change these sequences in here,

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at will, without having any effect
on the viability of the organism on

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it's selective, or
Darwinian, fitness,

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and therefore, such mutations
in these, in these sequences,

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are neutral mutation, they
have on effect on phenotype,

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and they will not be
eliminated from the gene pool.

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00:14:37,000 --> 00:14:40,000
Again here, mutations in these
vital, critical genes will be

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00:14:40,000 --> 00:14:43,000
eliminated from the gene pool.
So that's another one of the

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00:14:43,000 --> 00:14:46,000
principles in molecular evolution
that we want to talk about.

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00:14:46,000 --> 00:14:50,000
And if you follow these
principles, we can not only do, draw

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00:14:50,000 --> 00:14:53,000
evolutionary trees like this,
which have a grand scope, a scale of

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00:14:53,000 --> 00:14:56,000
three and a half billion years,
we can talk, for example, about how

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00:14:56,000 --> 00:15:00,000
different kinds of bears
are related to one another,

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00:15:00,000 --> 00:15:03,000
and on the basis, once
again, of their DNA sequence.

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00:15:03,000 --> 00:15:06,000
Or, if you want, we can even
look at how different kinds of

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domesticated animals are
related to one another.

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This is kind of a fun undertaking.
Look at this. Why is it fun? Well

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it's, it's kind of an amusing idea,
how often were cows domesticated

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00:15:19,000 --> 00:15:23,000
during the history of humanity?
How often were sheep domesticated?

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Pigs, water buffalos, and horses.
And what you see here is that cattle

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were domesticated on two occasions,
probably once in Western Asia, the

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00:15:32,000 --> 00:15:37,000
middle east, and once in Eastern
Asia. Sheep were domesticated twice,

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00:15:37,000 --> 00:15:42,000
all modern sheep following
these two families here.

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00:15:42,000 --> 00:15:46,000
Obviously they share a
common ancestor someway back,

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00:15:46,000 --> 00:15:50,000
but most sheep either fall here
or here. Pigs seem to have been

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00:15:50,000 --> 00:15:54,000
domesticated twice, once
over here and once over here,

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00:15:54,000 --> 00:15:58,000
water buffalos twice,
horses are very confusing,

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00:15:58,000 --> 00:16:02,000
it looks like they were domesticated
on several occasions because they're

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00:16:02,000 --> 00:16:06,000
all over the map, they're
not two clusters of

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00:16:06,000 --> 00:16:10,000
closely-related varieties,
like here and here. What others,

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00:16:10,000 --> 00:16:14,000
dogs, that's recently, I forget
what the number is for dogs, once.

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00:16:14,000 --> 00:16:18,000
Dogs were domesticated once,
probably the earliest domestication,

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00:16:18,000 --> 00:16:22,000
about 100,000 years ago. They all
have one common radiating tree,

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00:16:22,000 --> 00:16:26,000
here we have two radiating trees,
one cluster over here, one cluster

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00:16:26,000 --> 00:16:31,000
over here, with sheep, pigs,
and so fourth. So we can even,

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00:16:31,000 --> 00:16:35,000
so you can learn an enormous
amount about even the history of

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00:16:35,000 --> 00:16:40,000
agriculture, by looking at
these kinds of DNA pedigree.

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00:16:40,000 --> 00:16:44,000
Here's some other interesting
principles. Mitochondrial DNA

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00:16:44,000 --> 00:16:49,000
passes always from the mother, so
when a fertilized egg is formed,

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00:16:49,000 --> 00:16:53,000
Dad gives his chromosomes,
but he doesn't donate for any,

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00:16:53,000 --> 00:16:58,000
doesn't donate any mitochondrial
DNA. I remember visiting a friend in

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00:16:58,000 --> 00:17:03,000
North Carolina in 1974,
and he was looking at the

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00:17:03,000 --> 00:17:07,000
mitochondrial DNA of mules and,
when you breed a horse and a donkey,

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00:17:07,000 --> 00:17:12,000
what do you get out?
You get a mule out,

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00:17:12,000 --> 00:17:18,000
or, what happens if you do it
the other way? What happens if the

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00:17:18,000 --> 00:17:24,000
father is a horse, and
the mother is a donkey?

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00:17:24,000 --> 00:17:30,000
It's a hinny, it's actually called
a hinny. So there's two ways of

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00:17:30,000 --> 00:17:36,000
breeding, and the question is now,
and by the way, it's not so nice to

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00:17:36,000 --> 00:17:42,000
have a father being the horse
and the mother being the mule.

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00:17:42,000 --> 00:17:45,000
Why? Because Mom isn't used to
carrying an embryo that's much

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00:17:45,000 --> 00:17:49,000
larger than she's adapted to. The
other way is fine, because then

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00:17:49,000 --> 00:17:53,000
she can carry a small embryo, but
if Dad comes from a much larger

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00:17:53,000 --> 00:17:57,000
species, then the fetus that
the female donkey must carry,

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00:17:57,000 --> 00:18:00,000
is larger than her womb
is really evolved to carry.

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00:18:00,000 --> 00:18:04,000
So, you don't often see these
hinnies around because they cause

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00:18:04,000 --> 00:18:08,000
great difficulty at birth. In
any case, why did I get into

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00:18:08,000 --> 00:18:12,000
this digression?
Glad I asked that.

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00:18:12,000 --> 00:18:15,000
The question was, where did
the mitochondrial DNA come?

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00:18:15,000 --> 00:18:19,000
1974, this was still a hot
question. And it turned out,

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00:18:19,000 --> 00:18:22,000
the mitochondrial DNA in both the
mules and the hinnies came always

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00:18:22,000 --> 00:18:26,000
from Mom. There was not a trace of
mitochondrial DNA from the father

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00:18:26,000 --> 00:18:29,000
and, as a consequence, this
begins to cause us to realize

280
00:18:29,000 --> 00:18:33,000
where our mitochondrial DNA comes
from. So his mitochondrial DNA

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00:18:33,000 --> 00:18:36,000
comes from his mother,
his maternal grandmother,

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00:18:36,000 --> 00:18:40,000
her mother, her mother before her,
and so fourth, and the same for each

283
00:18:40,000 --> 00:18:43,000
one of you. And what
this means is that if you

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00:18:43,000 --> 00:18:47,000
look at a pedigree like this,
and for example, here we have a

285
00:18:47,000 --> 00:18:50,000
mother and a father,
girls are always round,

286
00:18:50,000 --> 00:18:54,000
boys are square. And here
you'll see the mitochondrial DNA,

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00:18:54,000 --> 00:18:57,000
it's donated to all of the children,
but the fact is that these boys,

288
00:18:57,000 --> 00:19:01,000
when they mate, when
they have offspring,

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00:19:01,000 --> 00:19:05,000
they will no longer pass
along her mitochondrial DNA,

290
00:19:05,000 --> 00:19:08,000
so it will be lost. And the
only way the mitochondrial

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00:19:08,000 --> 00:19:12,000
DNA can be transmitted is
through one of her daughters,

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00:19:12,000 --> 00:19:16,000
who in turn, have daughters.
Here you see the situation where

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00:19:16,000 --> 00:19:20,000
almost all of her mitochondrial
DNA is lost, except for this female

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00:19:20,000 --> 00:19:24,000
descendent who, once again,
passes it on to her sons

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00:19:24,000 --> 00:19:28,000
and daughters.
Only the daughters,

296
00:19:28,000 --> 00:19:33,000
again, can transmit mitochondrial
DNA. And there is equity in life,

297
00:19:33,000 --> 00:19:37,000
it doesn't often happen. Jack
Kennedy said life is unfair,

298
00:19:37,000 --> 00:19:41,000
but sometimes it's reasonably fair,
but here is the y-chromosomes, the

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00:19:41,000 --> 00:19:46,000
y-counterpart. Keep in
mind, the y-chromosome only

300
00:19:46,000 --> 00:19:50,000
passes from father-to-son, to
father-to-son, and exactly the

301
00:19:50,000 --> 00:19:54,000
same dynamics apply. And
importantly, this is critical

302
00:19:54,000 --> 00:19:58,000
for our thinking now, neither
the y-chromosome nor the

303
00:19:58,000 --> 00:20:02,000
mitochondrial DNA recombines
with another chromosome.

304
00:20:02,000 --> 00:20:06,000
And therefore, the complexities
of diploid mendelian genetics are

305
00:20:06,000 --> 00:20:10,000
obviated. So when you're looking at,
for example, the mitochondrial DNA,

306
00:20:10,000 --> 00:20:14,000
you can look at the pure
results of accumulated mutations,

307
00:20:14,000 --> 00:20:17,000
You don't have to worry
about crossing-over,

308
00:20:17,000 --> 00:20:21,000
you don't have to worry about
exchange of portions of a gene

309
00:20:21,000 --> 00:20:25,000
between two homologous chromosomes.
It doesn't happen with the

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00:20:25,000 --> 00:20:29,000
y-chromosome because there's
only one of them in the cell,

311
00:20:29,000 --> 00:20:33,000
and it doesn't happen with the
mitochondrial DNA because there's no

312
00:20:33,000 --> 00:20:37,000
other DNA for it to equilibrate
with. As a consequence,

313
00:20:37,000 --> 00:20:41,000
we can begin to think about what
happens with mitochondrial DNA and

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00:20:41,000 --> 00:20:45,000
y-chromosomal DNA, in
young and old species.

315
00:20:45,000 --> 00:20:48,000
So let's talk about a
recently formed species,

316
00:20:48,000 --> 00:20:52,000
and let's say we have a
young species down here,

317
00:20:52,000 --> 00:20:55,000
below the illustration, and
now this species, which has

318
00:20:55,000 --> 00:20:59,000
recently come into existence
for whatever reason,

319
00:20:59,000 --> 00:21:02,000
hangs around for the
next couple million years.

320
00:21:02,000 --> 00:21:06,000
And while it hangs around,
there will be random mutations,

321
00:21:06,000 --> 00:21:10,000
which strike the genomes of
individual members of that species.

322
00:21:10,000 --> 00:21:14,000
And therefore, the longer
the life of the species

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00:21:14,000 --> 00:21:18,000
as a whole, the more genetically
diverse will become the individuals

324
00:21:18,000 --> 00:21:22,000
in the species, and
therefore, this species will

325
00:21:22,000 --> 00:21:26,000
grow to have more and more genetic
diversity, just because of the

326
00:21:26,000 --> 00:21:30,000
random stochastic mutations that
accumulate in different peoples

327
00:21:30,000 --> 00:21:34,000
genomes in the course of the life of
this species, over millions of years.

328
00:21:34,000 --> 00:21:38,000
Again, keep in mind that the
vast majority of these accumulated

329
00:21:38,000 --> 00:21:42,000
mutations will be mutual mutations,
which will not affect phenotype, and

330
00:21:42,000 --> 00:21:46,000
therefore, they will not be
eliminated by Darwinian selection.

331
00:21:46,000 --> 00:21:50,000
And many of these neutral mutations,
which have no effect on organismic

332
00:21:50,000 --> 00:21:54,000
fitness, but are simply evolutionary
neutral, are sometimes called

333
00:21:54,000 --> 00:21:59,000
polymorphisms. The
term polymorphism,

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00:21:59,000 --> 00:22:03,000
-morph is once again morphology,
derives from the fact that species

335
00:22:03,000 --> 00:22:07,000
tend to be polymorphic, we
don't all have blond hair,

336
00:22:07,000 --> 00:22:11,000
we don't all have brown
eyes. We, as a species,

337
00:22:11,000 --> 00:22:15,000
have a great variability in
phenotype, we're polymorphic,

338
00:22:15,000 --> 00:22:18,000
and yet having black hair,
and having blond hair,

339
00:22:18,000 --> 00:22:22,000
and having red hair, none of
those is considered mutant,

340
00:22:22,000 --> 00:22:25,000
none of those is
considered pathological. I.

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00:22:25,000 --> 00:22:29,000
., among the group of normal
phenotypes, there's a whole series

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00:22:29,000 --> 00:22:32,000
of different gradations, and
these are considered normal

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00:22:32,000 --> 00:22:36,000
gradations in phenotype,
but at the genetic level,

344
00:22:36,000 --> 00:22:40,000
we talk about polymorphisms
in the same sense.

345
00:22:40,000 --> 00:22:43,000
Genetically distinct nucleotide
sequences, which again,

346
00:22:43,000 --> 00:22:47,000
are not pathological, they don't
create a disadvantageous phenotype.

347
00:22:47,000 --> 00:22:51,000
And as a consequence, they are
once again, not selected against.

348
00:22:51,000 --> 00:22:54,000
Now look what happens over
here. Here we have great genetic

349
00:22:54,000 --> 00:22:58,000
diversity, but what will happen is,
for one reason or another, only a

350
00:22:58,000 --> 00:23:02,000
small subset of individuals
constituting this species,

351
00:23:02,000 --> 00:23:06,000
will turn out to be the ancestors
of the successor species.

352
00:23:06,000 --> 00:23:09,000
Here's the next species that arises.
And why will these just be the

353
00:23:09,000 --> 00:23:13,000
ancestors? Well, everybody
else could get killed off

354
00:23:13,000 --> 00:23:16,000
through some plague, they
might get killed off by

355
00:23:16,000 --> 00:23:20,000
somebody going out and
purposefully killing them, or,

356
00:23:20,000 --> 00:23:23,000
it might just be that a meteor comes
down and wipes all these guys out,

357
00:23:23,000 --> 00:23:27,000
and these are the only ones in
here, from this small subset of the

358
00:23:27,000 --> 00:23:31,000
original species,
who end up surviving,

359
00:23:31,000 --> 00:23:34,000
and who end up becoming the
precursors, the ancestors,

360
00:23:34,000 --> 00:23:38,000
of the new species, and once
again, undergoes a period of

361
00:23:38,000 --> 00:23:42,000
diversification. And
what we have therefore,

362
00:23:42,000 --> 00:23:46,000
is a diversification and then
a collapse of genetic diversity.

363
00:23:46,000 --> 00:23:50,000
Here, this species, because
it came from a small group,

364
00:23:50,000 --> 00:23:54,000
is initially rather, rather
homogenous genetically,

365
00:23:54,000 --> 00:23:59,000
but with the passage of
evolutionary time, once again,

366
00:23:59,000 --> 00:24:03,000
there's evolutionary diversification.
So, an older species actually ends

367
00:24:03,000 --> 00:24:07,000
up being much more genetically
diverse than does the

368
00:24:07,000 --> 00:24:12,000
younger species. If you
look at two chimpanzees

369
00:24:12,000 --> 00:24:16,000
living on opposite sides of
the same hill in West Africa,

370
00:24:16,000 --> 00:24:20,000
they are genetically far more
distantly related to one another,

371
00:24:20,000 --> 00:24:24,000
than any one of us, by a factor
of 10 to 15. Two chimpanzees,

372
00:24:24,000 --> 00:24:28,000
they look exactly the same, they
have the same peculiar habits,

373
00:24:28,000 --> 00:24:32,000
but they're genetically far more
distantly-related than we are to

374
00:24:32,000 --> 00:24:36,000
one-another, than I am to any one
of you, or than any one of you is to

375
00:24:36,000 --> 00:24:40,000
one another. And
what does that mean?

376
00:24:40,000 --> 00:24:45,000
It means that,
roughly speaking,

377
00:24:45,000 --> 00:24:50,000
the species of chimpanzees is, at
least, 10 or 15 times older than

378
00:24:50,000 --> 00:24:56,000
our species are.
We're a young species,

379
00:24:56,000 --> 00:25:01,000
chimpanzees probably first speciated
three or four million years ago,

380
00:25:01,000 --> 00:25:07,000
if the paleontological record is,
is accurate. Paleontology is the

381
00:25:07,000 --> 00:25:12,000
study of old, dusty bones, so
you can begin to imagine when

382
00:25:12,000 --> 00:25:18,000
chimpanzee bones become
recognizable in the earth.

383
00:25:18,000 --> 00:25:22,000
So a paleontologist says that,
that chimps aren't that old, and it

384
00:25:22,000 --> 00:25:27,000
begins to suggest that our
species is only about 200,

385
00:25:27,000 --> 00:25:32,000
00 years old, at the oldest. Now
you say 200,000 years is a long

386
00:25:32,000 --> 00:25:36,000
time, but it isn't so long because
I started out this discussion talking

387
00:25:36,000 --> 00:25:41,000
about 3.5 billion years,
3.5 times ten to the ninth,

388
00:25:41,000 --> 00:25:46,000
and now I'm talking about
two times ten to the fourth.

389
00:25:46,000 --> 00:25:51,000
Is that right? No, two
times ten to the fifth.

390
00:25:51,000 --> 00:25:55,000
Four orders of magnitude difference.
So that means that our species, we

391
00:25:55,000 --> 00:25:59,000
went through a bottleneck
about 200-250,000 years ago,

392
00:25:59,000 --> 00:26:04,000
and because that is so recent, we
haven't had a chance to actually

393
00:26:04,000 --> 00:26:08,000
acquire much genetic diversity.
We're actually very closely related

394
00:26:08,000 --> 00:26:12,000
to one another, although
to talk to people,

395
00:26:12,000 --> 00:26:17,000
you'd think we were all very
distantly related to one another.

396
00:26:17,000 --> 00:26:21,000
Here's another interesting notion,
which also figures in, and that is,

397
00:26:21,000 --> 00:26:26,000
what happens in the genetics
of small populations?

398
00:26:26,000 --> 00:26:30,000
So here we started out with eight
individuals, and let's assume for a

399
00:26:30,000 --> 00:26:34,000
moment, that this population
has a steady size, i.

400
00:26:34,000 --> 00:26:38,000
. it doesn't increase or decrease
over the course of several

401
00:26:38,000 --> 00:26:42,000
generations. And what that
means is that each couple will,

402
00:26:42,000 --> 00:26:46,000
on average, leave behind two
children, and those two children

403
00:26:46,000 --> 00:26:50,000
will breed, and each of them will,
couples in the successor population,

404
00:26:50,000 --> 00:26:54,000
will leave behind two children.
And what you see already,

405
00:26:54,000 --> 00:26:58,000
in such small populations, is
that for example, this male here

406
00:26:58,000 --> 00:27:02,000
has two girls,
and right away,

407
00:27:02,000 --> 00:27:06,000
to the extent he had an interesting
y-chromosome, that y-chromosome was

408
00:27:06,000 --> 00:27:10,000
lost from the gene pool. This
girl, here, had an interesting

409
00:27:10,000 --> 00:27:14,000
mitochondrial DNA, but
right away that's lost,

410
00:27:14,000 --> 00:27:18,000
because she has, she has just
two boys. And what you see,

411
00:27:18,000 --> 00:27:22,000
in very rapid order, in
small populations, there's a

412
00:27:22,000 --> 00:27:26,000
homogenization of the genetic
compliment, just because the alleles

413
00:27:26,000 --> 00:27:30,000
are lost within what's
called, genetic drift.

414
00:27:30,000 --> 00:27:34,000
And as a consequence,
very rapidly, there becomes

415
00:27:34,000 --> 00:27:38,000
homozygosity at many loci
in very small populations.

416
00:27:38,000 --> 00:27:42,000
A real-life situation comes
from Mutiny on the Bounty,

417
00:27:42,000 --> 00:27:46,000
where Fletcher Christian ends
up getting shipwrecked on,

418
00:27:46,000 --> 00:27:50,000
what island was it, Pitcairn Island,
which is somewhere on the South

419
00:27:50,000 --> 00:27:54,000
Pacific, South Atlantic, I
forget where. Anyhow, today if

420
00:27:54,000 --> 00:27:58,000
you go to Pitcairn Island,
almost everybody is called,

421
00:27:58,000 --> 00:28:02,000
almost everybody has a
family name, Christian.

422
00:28:02,000 --> 00:28:05,000
Why? Was it that he was more studly
and fecund than everybody else?

423
00:28:05,000 --> 00:28:08,000
Probably not. What probably
happened was, in the same dynamics

424
00:28:08,000 --> 00:28:12,000
that dictates the
homogenization of y-chromosomes,

425
00:28:12,000 --> 00:28:15,000
dictates the homogenization
of family names. So,

426
00:28:15,000 --> 00:28:18,000
if you isolate people in a
small demographic isolate,

427
00:28:18,000 --> 00:28:22,000
like an island in the middle of the
ocean, over a period of generations,

428
00:28:22,000 --> 00:28:25,000
roughly equal to, I think, twice the
number of individuals in the steady,

429
00:28:25,000 --> 00:28:28,000
state population, everybody
will have the same family name,

430
00:28:28,000 --> 00:28:32,000
because the other family names will,
by chance, in a small population,

431
00:28:32,000 --> 00:28:36,000
just be lost. On my
father's side of the family,

432
00:28:36,000 --> 00:28:40,000
I have hundreds of cousins with my
family name, and on my mother's side

433
00:28:40,000 --> 00:28:44,000
of the family,
not a single one,

434
00:28:44,000 --> 00:28:48,000
just as an example of this kind of
trait. Now keep in mind that this

435
00:28:48,000 --> 00:28:52,000
evolutionary diversification
can also affect the y-chromosome,

436
00:28:52,000 --> 00:28:56,000
so therefore, there are different
y-chromosomes across the face of the

437
00:28:56,000 --> 00:29:00,000
planet, which can be distinguished,
not because they're better or lesser

438
00:29:00,000 --> 00:29:04,000
y-chromosomes, in terms
of the phenotype of

439
00:29:04,000 --> 00:29:08,000
maleness, but because they've
accumulated polymorphisms

440
00:29:08,000 --> 00:29:12,000
over a period of time. They
may be single-nucleotide

441
00:29:12,000 --> 00:29:16,000
polymorphisms, but
these single-nucleotide

442
00:29:16,000 --> 00:29:20,000
polymorphisms can be used
to determine how closely,

443
00:29:20,000 --> 00:29:24,000
or distantly related, are
individuals to one another.

444
00:29:24,000 --> 00:29:28,000
Let's look at the mitochondrial
DNA of women in western Europe,

445
00:29:28,000 --> 00:29:33,000
and if you look at the mitochondrial
DNA of women in western Europe,

446
00:29:33,000 --> 00:29:37,000
you find that they only have,
how many different things there?

447
00:29:37,000 --> 00:29:41,000
One, two, three, four, five,
six, seven, there's seven basic

448
00:29:41,000 --> 00:29:45,000
types of mitochondrial DNA that
are found in western and northern

449
00:29:45,000 --> 00:29:50,000
European women. And
what that means is,

450
00:29:50,000 --> 00:29:55,000
inescapably, people who
live in modern-day Europe,

451
00:29:55,000 --> 00:30:00,000
descend from seven women who had
these respective mitochondrial DNA

452
00:30:00,000 --> 00:30:05,000
sequences. When did those
seven ancestors live,

453
00:30:05,000 --> 00:30:10,000
well we don't really know, probably
between 10-15,000 years ago.

454
00:30:10,000 --> 00:30:15,000
But, the western-European
population descends from an

455
00:30:15,000 --> 00:30:20,000
stunningly small
number of founders.

456
00:30:20,000 --> 00:30:22,000
Now clearly, DNA sequencing is
terrific, but it's not good enough

457
00:30:22,000 --> 00:30:25,000
to know the names of those women,
so I can tell you that they were not

458
00:30:25,000 --> 00:30:27,000
named Velda and Jasmine.
[LAUGHTER] Anyhow, but here you

459
00:30:27,000 --> 00:30:30,000
can see, here you can, now
obviously, these women in turn

460
00:30:30,000 --> 00:30:32,000
were related to one another, you
can ask, you can do another kind

461
00:30:32,000 --> 00:30:35,000
of question. How much are all of
our mitochondrial DNA are related to

462
00:30:35,000 --> 00:30:37,000
one another, how distantly
related are they to one another,

463
00:30:37,000 --> 00:30:40,000
given the rate of evolution
of mitochondrial DNA sequences?

464
00:30:40,000 --> 00:30:45,000
And if you ask that question,
the answer is that we all had a

465
00:30:45,000 --> 00:30:51,000
common ancestress who lived
about 150,000 years ago.

466
00:30:51,000 --> 00:30:57,000
All of us trace our mitochondrial
DNA to her. Does that mean that

467
00:30:57,000 --> 00:31:02,000
there was only one woman alive there,
she's called, Mitochondrial-Eve,

468
00:31:02,000 --> 00:31:08,000
again, we don't know her name. Does
that mean there was only one woman

469
00:31:08,000 --> 00:31:14,000
alive, well it doesn't mean that at
all because of what I just told you,

470
00:31:14,000 --> 00:31:20,000
in small populations the
proto-human population.

471
00:31:20,000 --> 00:31:24,000
I just told you that certain
polymorphisms die out because of

472
00:31:24,000 --> 00:31:28,000
this genetic drift, because
of these stochastic events.

473
00:31:28,000 --> 00:31:32,000
And so, the founding human
population could have had 20,

474
00:31:32,000 --> 00:31:36,000
50,100 individuals in it, but one
woman's mitochondrial DNA happened

475
00:31:36,000 --> 00:31:41,000
because of these accidents
to dominate, so that now,

476
00:31:41,000 --> 00:31:45,000
all of us have the same,
are the descendents of her

477
00:31:45,000 --> 00:31:49,000
mitochondrial DNA. Clearly,
in the intervening time

478
00:31:49,000 --> 00:31:53,000
since 150,000 years ago,
accumulated mutations have,

479
00:31:53,000 --> 00:31:57,000
have altered subtly the
mitochondrial DNA genome,

480
00:31:57,000 --> 00:32:02,000
so there's polymorphisms,
And so one can make,

481
00:32:02,000 --> 00:32:08,000
one can drive phylogenies of
different kinds of mitochondrial DNA,

482
00:32:08,000 --> 00:32:13,000
and look at the relatedness
between different clades,

483
00:32:13,000 --> 00:32:19,000
different groups, of
women in modern-day Europe.

484
00:32:19,000 --> 00:32:24,000
70% of Finish men, in
Finland, have a y-chromosome

485
00:32:24,000 --> 00:32:30,000
polymorphism that is otherwise
virtually unheard of in the rest of

486
00:32:30,000 --> 00:32:36,000
Europe. 70% of Finish men,
now what does that mean?

487
00:32:36,000 --> 00:32:38,000
Well, to me to means that those
70% of Finish men descended from a

488
00:32:38,000 --> 00:32:41,000
common ancestor, a
male who lived around,

489
00:32:41,000 --> 00:32:44,000
if you look at the sequences,
who lived around two or three

490
00:32:44,000 --> 00:32:47,000
thousand years ago, and
who, for some reason,

491
00:32:47,000 --> 00:32:50,000
became the ancestor of all the
people living in modern Finland.

492
00:32:50,000 --> 00:32:52,000
That's extraordinary. There's four
million people living in Finland

493
00:32:52,000 --> 00:32:55,000
today, and the males all have their
inherit, inherit their y-chromosome

494
00:32:55,000 --> 00:32:58,000
from that man, we don't
know exactly where he lived,

495
00:32:58,000 --> 00:33:01,000
But obviously
the modern Finish

496
00:33:01,000 --> 00:33:05,000
population descends from a very
small founder-group who came into

497
00:33:05,000 --> 00:33:09,000
what we call, modern Finland,
relatively recently, maybe two-two

498
00:33:09,000 --> 00:33:13,000
and a half thousand years ago,
and thereafter, did not freely

499
00:33:13,000 --> 00:33:16,000
interbreed with the rest
of the European population.

500
00:33:16,000 --> 00:33:20,000
How do we know that?
Because that y-chromosomal

501
00:33:20,000 --> 00:33:24,000
polymorphism is not present
elsewhere, it's only present in

502
00:33:24,000 --> 00:33:28,000
Finland. So it was a genetic,
and obviously linguistic, isolate.

503
00:33:28,000 --> 00:33:32,000
So where do we
all come from,

504
00:33:32,000 --> 00:33:36,000
all of us human beings? How closely
related are we to one another?

505
00:33:36,000 --> 00:33:40,000
Here's, here's a measurement of
the distances between different

506
00:33:40,000 --> 00:33:44,000
mitochondrial DNA's from
different branches of humanity.

507
00:33:44,000 --> 00:33:49,000
And what you see is something
really quite extraordinary and

508
00:33:49,000 --> 00:33:53,000
stunning. Here, you'll
see that the people,

509
00:33:53,000 --> 00:33:57,000
the non-African lineages here
and here, are actually relatively

510
00:33:57,000 --> 00:34:01,000
closely related to one another.
But if you look at the people who

511
00:34:01,000 --> 00:34:04,000
live in Africa, down here,
there is enormous genetic

512
00:34:04,000 --> 00:34:08,000
diversity. Look how far these
evolutionary branches reach back,

513
00:34:08,000 --> 00:34:11,000
look how long these are. The
distance of these branches,

514
00:34:11,000 --> 00:34:14,000
of these roots, determines how
far, how distantly related these

515
00:34:14,000 --> 00:34:18,000
individuals are,
one to the other.

516
00:34:18,000 --> 00:34:21,000
And on the basis of that, and
on the basis of a lot of other

517
00:34:21,000 --> 00:34:24,000
auxiliary genetic information, we
can conclude that Africa was the

518
00:34:24,000 --> 00:34:28,000
site where genetic diversification
was generated during

519
00:34:28,000 --> 00:34:31,000
human evolution. And
that what happened,

520
00:34:31,000 --> 00:34:35,000
as a consequence of
that diversification,

521
00:34:35,000 --> 00:34:39,000
is starting over the last 40,
50, 60,000 years ago, different

522
00:34:39,000 --> 00:34:42,000
populations, different sub-populations,

523
00:34:42,000 --> 00:34:46,000
small, isolated sub-populations,
migrated out of Africa, took a very

524
00:34:46,000 --> 00:34:49,000
small sub-set of the polymorphisms
with them, and became the

525
00:34:49,000 --> 00:34:53,000
founder-populations of a whole
variety of whole different

526
00:34:53,000 --> 00:34:57,000
modern-day populations. These
populations here are largely

527
00:34:57,000 --> 00:35:00,000
Mongoloid, these populations
here are largely Caucasian,

528
00:35:00,000 --> 00:35:04,000
and here, we see that in
Africa there's enormous genetic

529
00:35:04,000 --> 00:35:07,000
diversity.
And by the way,

530
00:35:07,000 --> 00:35:11,000
all the genes that are present here,
the alleles that are present here,

531
00:35:11,000 --> 00:35:15,000
can also be found in Africa, but
in relatively small proportions

532
00:35:15,000 --> 00:35:19,000
in Africa. And we know this kind
of diversity exists both for the

533
00:35:19,000 --> 00:35:23,000
mitochondrial DNA, and here's
for the y-chromosomal DNA,

534
00:35:23,000 --> 00:35:26,000
again, we look for polymorphisms.
And this is not a very good

535
00:35:26,000 --> 00:35:30,000
overhead, again, the
reproduction was not very good,

536
00:35:30,000 --> 00:35:34,000
but what I'm showing you is that
the evolutionary, the depth of these

537
00:35:34,000 --> 00:35:38,000
evolutionary branches is enormous
in Africa, yet in other parts of the

538
00:35:38,000 --> 00:35:42,000
globe, people are much more
closely-related to one another.

539
00:35:42,000 --> 00:35:45,000
Some people argue on the basis of
the genetic-relatedness of western

540
00:35:45,000 --> 00:35:48,000
and northern Europeans, that
the modern European population

541
00:35:48,000 --> 00:35:52,000
is largely descended from about 20
couples that moved into Europe about

542
00:35:52,000 --> 00:35:55,000
10,000 years ago, eight
to ten thousand years ago,

543
00:35:55,000 --> 00:35:58,000
at the time when agriculture was
introduced into Europe from the

544
00:35:58,000 --> 00:36:02,000
middle east, just on the basis
of looking at these y-chromosomal

545
00:36:02,000 --> 00:36:06,000
sequences. And so,
we human beings arose,

546
00:36:06,000 --> 00:36:11,000
even though we are reasonably
distantly related to one another on

547
00:36:11,000 --> 00:36:16,000
this graph, keep in mind that we as
a species, are enormously close to

548
00:36:16,000 --> 00:36:21,000
one another because of the
youth of this, of our species.

549
00:36:21,000 --> 00:36:26,000
If you look at our, the time of
this diversification was probably

550
00:36:26,000 --> 00:36:31,000
sometime between 80-100, 00
years ago, so how did it all

551
00:36:31,000 --> 00:36:36,000
happen? We can even figure out the
history of humanity by beginning to

552
00:36:36,000 --> 00:36:42,000
look at these different
kinds of polymorphisms.

553
00:36:42,000 --> 00:36:45,000
A long time ago, individuals
went out from Africa,

554
00:36:45,000 --> 00:36:49,000
maybe starting 100,000 years
ago, maybe starting more recently,

555
00:36:49,000 --> 00:36:53,000
and went across the southern rim
of Eurasia, and we know already,

556
00:36:53,000 --> 00:36:56,000
we find archeological remains of
Aborigines in Australia between

557
00:36:56,000 --> 00:37:00,000
40-60,000 years ago. And
by the way, those people are

558
00:37:00,000 --> 00:37:04,000
very distantly related to the
rest of us, having left and not

559
00:37:04,000 --> 00:37:08,000
intermingled with the rest
of humanity for a very long

560
00:37:08,000 --> 00:37:11,000
period of time. There were
Aborigines in Australia,

561
00:37:11,000 --> 00:37:15,000
already at a time when our ancestors,
to the extent we had ancestors in

562
00:37:15,000 --> 00:37:19,000
Europe, were still battling the
Neanderthals, who only died out 30,

563
00:37:19,000 --> 00:37:23,000
00 years ago. You may know by
the way, you may have read in the

564
00:37:23,000 --> 00:37:27,000
newspaper, about a month ago,
they discovered skeletons of very

565
00:37:27,000 --> 00:37:30,000
small people on an island Indonesia.
In fact, those were probably not

566
00:37:30,000 --> 00:37:34,000
even homosapiens, those
were probably a precursor

567
00:37:34,000 --> 00:37:38,000
species, because we know over
the last two million years,

568
00:37:38,000 --> 00:37:42,000
there have been hominoids,
look like human beings but are

569
00:37:42,000 --> 00:37:46,000
precursors, who might migrated out
of Africa, who dispersed throughout

570
00:37:46,000 --> 00:37:50,000
Asia, and who eventually
became extinct,

571
00:37:50,000 --> 00:37:53,000
So that the only modern human who
exist are the descendents of this

572
00:37:53,000 --> 00:37:57,000
out migration that began about 100,
00 years ago. We know that about 15,

573
00:37:57,000 --> 00:38:00,000
00 years ago some of these
people ended up going over here,

574
00:38:00,000 --> 00:38:04,000
to crossing in four different waves
of migration, you can see it from

575
00:38:04,000 --> 00:38:08,000
the DNA, into the
western hemisphere.

576
00:38:08,000 --> 00:38:12,000
Amerindians, that is, American
Indians, Native Americans,

577
00:38:12,000 --> 00:38:16,000
are genetically rather homogenous.
Why? Because they all descend from

578
00:38:16,000 --> 00:38:21,000
very small founder populations that
came into the western hemisphere

579
00:38:21,000 --> 00:38:25,000
relatively recently. And
there's enormous genetic

580
00:38:25,000 --> 00:38:30,000
homogeneity among different
subgroups of individuals here in

581
00:38:30,000 --> 00:38:34,000
South America. Speaking
of South America,

582
00:38:34,000 --> 00:38:39,000
if you look in some parts of
Venezuela, what you find is that the

583
00:38:39,000 --> 00:38:43,000
mitochondrial DNA is
largely of Indian-origin,

584
00:38:43,000 --> 00:38:48,000
but the y-chromosomal DNA is
largely of European origin.

585
00:38:48,000 --> 00:38:52,000
So, what happens there, that's
a testimonial to the tragic

586
00:38:52,000 --> 00:38:56,000
fate of the Indians, where
the conquistadors from Spain

587
00:38:56,000 --> 00:39:00,000
came in, killed all the men, and
took all the women, to be their

588
00:39:00,000 --> 00:39:04,000
brides. How else can you explain
the fact that there's no Indian

589
00:39:04,000 --> 00:39:08,000
y-chromosomes, there's
all, there is instead only

590
00:39:08,000 --> 00:39:12,000
European y-chromosomes. And
here you can begin to see what

591
00:39:12,000 --> 00:39:16,000
happened here in New York, as
well. 40,000 years ago people

592
00:39:16,000 --> 00:39:21,000
started trickling into Europe,
and they hung around there for the

593
00:39:21,000 --> 00:39:26,000
next 30,000 years,
pretty much on their own.

594
00:39:26,000 --> 00:39:30,000
The remnants of those people
who came in, we know from DNA,

595
00:39:30,000 --> 00:39:35,000
are the Basques who live in
northern Spain, who speak,

596
00:39:35,000 --> 00:39:40,000
by the way, a non-indo
European language.

597
00:39:40,000 --> 00:39:43,000
They're the relics of this initial
settlement by modern humans of

598
00:39:43,000 --> 00:39:47,000
Europe, starting 40, 00
years ago. And they had the

599
00:39:47,000 --> 00:39:50,000
continent for themselves
for the next 30,000 years,

600
00:39:50,000 --> 00:39:54,000
until this new founder
population came in, about 10,

601
00:39:54,000 --> 00:39:57,000
00 years ago. Here's the names of
the girls who were in that group,

602
00:39:57,000 --> 00:40:01,000
Ursula and Katrine and Zenya, Tara,
Jasmine, and Velda, and they became

603
00:40:01,000 --> 00:40:04,000
the modern agriculturalists, and
swamped out the people who were

604
00:40:04,000 --> 00:40:08,000
there 40,000 years ago, who
now only survive as a relic

605
00:40:08,000 --> 00:40:12,000
population. Here's a
fun story I like to tell

606
00:40:12,000 --> 00:40:16,000
each year, and it's about
the Cohen and y-chromosome,

607
00:40:16,000 --> 00:40:21,000
and you'll see what an amusing
story this is, just from genetics.

608
00:40:21,000 --> 00:40:25,000
Now the name Cohen, in
Hebrew means, a high priest,

609
00:40:25,000 --> 00:40:29,000
and you've heard people named Cohen,
it's not such an uncommon name among

610
00:40:29,000 --> 00:40:34,000
the Jews. And it says, in the
Bible, in Genesis and Exodus,

611
00:40:34,000 --> 00:40:38,000
that all the high priests in the
Bible are the descendents of Aaron,

612
00:40:38,000 --> 00:40:43,000
the brother of Moses. And
it's also been the practice for

613
00:40:43,000 --> 00:40:47,000
the last 3,000 years, that
the only person who can become,

614
00:40:47,000 --> 00:40:51,000
the only male who can become
a Cohen, is the son of a Cohen.

615
00:40:51,000 --> 00:40:56,000
In other words, you cannot be
adopted into a family and acquire

616
00:40:56,000 --> 00:41:00,000
the name Cohen. And
if that's all true,

617
00:41:00,000 --> 00:41:05,000
and if the Bible is true, and
Aaron lived 3,000 years ago,

618
00:41:05,000 --> 00:41:09,000
whatever his name was, then it
should be the case that all male

619
00:41:09,000 --> 00:41:14,000
Cohen's should have the
same y-chromosome, right?

620
00:41:14,000 --> 00:41:17,000
Because they all descend,
their family name is Cohen,

621
00:41:17,000 --> 00:41:21,000
they could only get it from their
father, they could only get their

622
00:41:21,000 --> 00:41:25,000
y-chromosome from their father,
so they should all have the same

623
00:41:25,000 --> 00:41:29,000
y-chromosome. Of course, you
say that can't really be the

624
00:41:29,000 --> 00:41:32,000
case, because we know in
this country, in this country,

625
00:41:32,000 --> 00:41:36,000
between five and ten percent
of people, on average,

626
00:41:36,000 --> 00:41:40,000
are sending Father's Day
cards to the wrong person.

627
00:41:40,000 --> 00:41:44,000
What does that
mean? Non-paternity.

628
00:41:44,000 --> 00:41:48,000
When you do genetic counseling
of family these days,

629
00:41:48,000 --> 00:41:53,000
one of the strictures is, that
you never tell the family if

630
00:41:53,000 --> 00:41:57,000
the children have genetic
polymorphisms that don't match that

631
00:41:57,000 --> 00:42:02,000
of the person whom they think is
their father. They don't look like

632
00:42:02,000 --> 00:42:06,000
their, the person whom they regard
as father, but that's always assumed

633
00:42:06,000 --> 00:42:11,000
to be a role of the genetic dice.
So, how is that relevant? Well,

634
00:42:11,000 --> 00:42:16,000
let's talk about this descent from
Aaron, who lived 3,000 years ago.

635
00:42:16,000 --> 00:42:20,000
We're talking about the y-chromosome
being passed from one generation to

636
00:42:20,000 --> 00:42:24,000
the next, just like the family name.
So what happened, what would happen

637
00:42:24,000 --> 00:42:29,000
if sometime over the last 3, 00
years, Mrs. Cohen had a dalliance,

638
00:42:29,000 --> 00:42:33,000
had an affair, with a
television repairman,

639
00:42:33,000 --> 00:42:37,000
or the milkman, or the mailman,
and never told Mr. Cohen? The

640
00:42:37,000 --> 00:42:42,000
y-chromosome, which her son
thought he was getting from Dad,

641
00:42:42,000 --> 00:42:46,000
wouldn't be coming from Dad,
it'd be coming from this other,

642
00:42:46,000 --> 00:42:51,000
the milkman or the mailman, and
it wouldn't be a Cohen-y chromosome

643
00:42:51,000 --> 00:42:55,000
unless, by chance, the
mailman or the milkman also

644
00:42:55,000 --> 00:43:00,000
happened to be a Cohen,
[LAUGHTER], it could happen.

645
00:43:00,000 --> 00:43:04,000
But the chances are, roughly
speaking, Cohen's are only

646
00:43:04,000 --> 00:43:08,000
four percent of all Jews, so
the chances are against that

647
00:43:08,000 --> 00:43:12,000
happening. OK, so they
did this experiment,

648
00:43:12,000 --> 00:43:16,000
and this is really astounding
experiment. They went,

649
00:43:16,000 --> 00:43:20,000
the story is they went to a beach in
Tel Aviv, I don't know whether they

650
00:43:20,000 --> 00:43:24,000
actually did that or not, and
they picked up, they picked up

651
00:43:24,000 --> 00:43:28,000
100 male Cohen's who were Ashkenazi
, Ashkenazi means their ancestors came

652
00:43:28,000 --> 00:43:32,000
from central Europe, over here.
And they picked up 100 Sefardi

653
00:43:32,000 --> 00:43:36,000
Cohen's, and the Sefardi
Cohen's come from Spain,

654
00:43:36,000 --> 00:43:40,000
North Africa, Egypt, Yemen,
Iraq, Iran, Uzbekistan,

655
00:43:40,000 --> 00:43:44,000
Central Asia. And the last time
that the Iraqi Cohen's and the

656
00:43:44,000 --> 00:43:48,000
Ashkenazi Cohen's were
interbreeding, were about 500 BC,

657
00:43:48,000 --> 00:43:52,000
at the time of the Babylonian XL,
so they've been apart a long time.

658
00:43:52,000 --> 00:43:56,000
And they looked at
their y-chromosomes,

659
00:43:56,000 --> 00:44:00,000
and what they found was that 70%
of the y-chromosomes of these male

660
00:44:00,000 --> 00:44:04,000
Cohen's, 70% of the Cohen's
shared the same y-chromosome.

661
00:44:04,000 --> 00:44:07,000
Well, the same y-chromosome was
present only in 15% of non-Cohen,

662
00:44:07,000 --> 00:44:11,000
Israeli Jews. Now think about that
for a second. 70% of these men had

663
00:44:11,000 --> 00:44:14,000
the same y-chromosome, of
course they didn't know they had

664
00:44:14,000 --> 00:44:18,000
the same y-chromosome, all
they knew was that they had the

665
00:44:18,000 --> 00:44:22,000
same family name.
And what that means,

666
00:44:22,000 --> 00:44:25,000
inescapably, is that over a period
of two or three thousand years,

667
00:44:25,000 --> 00:44:29,000
it was hard to trace with exactitude
when the common male ancestor lived,

668
00:44:29,000 --> 00:44:32,000
over a period of two
or three thousand years,

669
00:44:32,000 --> 00:44:36,000
somehow the milkman and the
mailman stayed away from Mrs.

670
00:44:36,000 --> 00:44:40,000
Cohen, or Mrs. Cohen
was unusually virtuous.

671
00:44:40,000 --> 00:44:43,000
Because keep in mind, any
single affair with the milkman

672
00:44:43,000 --> 00:44:47,000
or the mailman,
over 3,000 years,

673
00:44:47,000 --> 00:44:50,000
would've broke this chain of
inheritance, any single incidence of

674
00:44:50,000 --> 00:44:54,000
non-paternity. It's a
really astounding story,

675
00:44:54,000 --> 00:44:57,000
and it's hard, there
can be no artifact to it,

676
00:44:57,000 --> 00:45:01,000
there's no bias in it, there's
no other way to explain it.

677
00:45:01,000 --> 00:45:04,000
And you can begin to find similar
stories of families in England,

678
00:45:04,000 --> 00:45:08,000
where males are tenth cousins of one
another, they have the same family

679
00:45:08,000 --> 00:45:12,000
name, and they also have
the same y-chromosome.

680
00:45:12,000 --> 00:45:17,000
The most amusing commentary on this
stems from a tribe that lives in

681
00:45:17,000 --> 00:45:22,000
southern Africa, and
these people are called,

682
00:45:22,000 --> 00:45:27,000
Lemba, L-e-m-b-a. And the, the myth
of the Lemba is that they descend

683
00:45:27,000 --> 00:45:32,000
from Jews who came down from
the north, Jewish traitors.

684
00:45:32,000 --> 00:45:37,000
So just for the hell of it, some
geneticists went down and drew

685
00:45:37,000 --> 00:45:42,000
blood from the male Lembas, and
there's four casts of Lembas,

686
00:45:42,000 --> 00:45:47,000
there's the ruling class, there's
the warriors, there's the farmers,

687
00:45:47,000 --> 00:45:51,000
the merchants, I don't know.
And what they found was that all

688
00:45:51,000 --> 00:45:55,000
members of the, almost
all members of the ruling

689
00:45:55,000 --> 00:45:59,000
cast among the Lembas,
had the same y-chromosome,

690
00:45:59,000 --> 00:46:02,000
and the y-chromosome had exactly
the same polymorphisms of the Cohen

691
00:46:02,000 --> 00:46:06,000
y-chromosome. No one in the other,
no males in the other three casts

692
00:46:06,000 --> 00:46:10,000
had, or very few, had
otherwise this y-chromosomal

693
00:46:10,000 --> 00:46:14,000
polymorphism. Go figure, I
don't know what's going on.

694
00:46:14,000 --> 00:46:17,000
Now did those people look Jewish?
Well, they looked like everybody

695
00:46:17,000 --> 00:46:20,000
else around them,
because if there was a Mr.

696
00:46:20,000 --> 00:46:23,000
Cohen who came down there,
three or four hundred years ago,

697
00:46:23,000 --> 00:46:27,000
and married in, he obviously
married one of the local population.

698
00:46:27,000 --> 00:46:30,000
And there were no other people
around from, coming in from the

699
00:46:30,000 --> 00:46:33,000
north, to marry to, so that
99% of the males in this

700
00:46:33,000 --> 00:46:37,000
ruling cast, who have the Cohen
y-chromosome, 99% of their genes

701
00:46:37,000 --> 00:46:40,000
come from the local population,
the only thing they inherited from

702
00:46:40,000 --> 00:46:44,000
Mr. Cohen was the y-chromosome.
Where else would they get their

703
00:46:44,000 --> 00:46:48,000
genes? There wasn't a massive
migration from the middle east down

704
00:46:48,000 --> 00:46:52,000
to the Lemba tribes, probably
just one man came down

705
00:46:52,000 --> 00:46:56,000
selling trinkets,
or who-knows-what,

706
00:46:56,000 --> 00:47:00,000
television sets, or VCRs, sometime
over the last three or four

707
00:47:00,000 --> 00:47:04,000
hundred years. And
somehow, for reasons that we

708
00:47:04,000 --> 00:47:08,000
have no idea, he became the ancestor
of this cast of people in this tribe

709
00:47:08,000 --> 00:47:12,000
in the middle of Africa. And
so you have stories that you

710
00:47:12,000 --> 00:47:16,000
begin to pick up, which
are stranger than fiction,

711
00:47:16,000 --> 00:47:20,000
some of the weirdest stories that
you've ever heard of in your life.

712
00:47:20,000 --> 00:47:24,000
Imagine having 3,000 years of
uninterrupted transmission from,

713
00:47:24,000 --> 00:47:28,000
without a single
case of non-paternity.

714
00:47:28,000 --> 00:47:32,000
It didn't happen all the cases,
because I didn't say 100% of the

715
00:47:32,000 --> 00:47:36,000
Cohen men had it, on
30% of the occasions,

716
00:47:36,000 --> 00:47:40,000
there must have been some snipping
of this chain of transmission.

717
00:47:40,000 --> 00:47:52,000
And keep in mind that this chain of
transmission happened over a period

718
00:47:52,000 --> 00:48:04,000
of enormous political and upheaval,
over the last 3,000 years. The

719
00:48:04,000 --> 00:48:17,000
middle east, and Europe, and
North Africa, have not been

720
00:48:17,000 --> 00:48:29,000
tranquil places over that period of
time. Enormous population dispersal,

721
00:48:29,000 --> 00:48:42,000
and confusion,
and displacement,

722
00:48:42,000 --> 00:48:54,000
and yet we now begin to look, by
looking at the DNA, we can begin

723
00:48:54,000 --> 00:49:07,000
to see all kinds of
really interesting things.

724
00:49:07,000 --> 00:49:11,000
Next, on Friday, Eric is
going to talk with you,

725
00:49:11,000 --> 00:49:16,000
I believe, on Monday, as well. And
Wednesday, we're going to talk about

726
00:49:16,000 --> 00:49:20,000
a related topic,
which is, how do all,

727
00:49:20,000 --> 00:49:25,000
how do these human genetic
differences have implications for

728
00:49:25,000 --> 00:49:29,000
the way we think about one another,
and the way that we will develop?

729
00:49:29,000 --> 00:49:34,000
See you then, a
week from today.