I’m here today to talk to you guys about
jeans and when I say jeans I don’t mean
that I don’t mean the jeans you’re
wearing but rather the jeans you’re
carrying your DNA so to start off I
thought we’d talk really quickly about
some things you might have heard about
your jeans that you’re wondering about
first of all you might have heard that
you share 99% of them with chimpanzees
which are closest living relative and
that is absolutely true you might have
also heard that there is less DNA in you
in each of your cells then there is an
in those of a humble onion and that is
also true
and lastly who amongst you hasn’t heard
on TV or read on Facebook or on any
other sources that scientists have
discovered the gene for things like
crime or maybe autism or cancer or
beauty or attraction or really any other
number of traits
well I’m gonna tell you something and
that’s something is that that is wrong
and I’m gonna tell you why
so these days it’s really really
fashionable to attribute all kinds of
phenomenal powers to our DNA so the
degree that you might start to wonder if
there’s really any reason in trying to
fight your genetic testing what makes
you you and makes me me is the argument
goes innate it’s something you’re born
with it’s your DNA and you know some of
you might actually find that comforting
because if you’re destined to gain
weight no matter what then you might as
well enjoy yourself at lunch and stop
feeling guilty about it you know why try
to fight this everybody knows you can’t
actually win against your DNA but is
that really true you know is your DNA
really all that powerful and this is a
question you might have asked yourself
before and it’s indeed a question you
might have heard of before because it
has been referred to for a long time as
the question of nature versus nurture
okay so sometimes it’s very true that
there is nothing you can do against your
DNA and let me give you a pretty
sobering example and instead of
Huntington’s disease it is a terrible
terrible disease
one in which the cells in your brain
become down
and slowly die and so you will rapidly
lose your ability to control both their
body on your mind and there’s a cease
for which there is endure treatment nor
cure it is also a fully genetic disease
all it takes is a single damaged copy of
a single gene if you have that copy you
will get the disease it is unavoidable
but not all diseases and not all traits
in fact behave like this just because
one of your parents had cancer does not
mean that you two necessarily will have
cancer even though you inherited half of
your DNA from that parent and the same
is true in fact of many traits traits
like height and weight and even
intelligence and also of complex
diseases of things like diabetes or
heart disease for instance you could be
the child of the tallest two people on
earth but if you were malnourished as an
infant it is extremely unlikely that you
will be as tall as they are so sometimes
your life experiences Trump your genes
nice and easy
sometimes nurture wins and in fact if
you look back fifty years a hundred
years ago you’ll find that most
philosophers strongly denied that nature
had any role in shaping humans the only
thing that mattered was nurture the only
thing that matter was experience nothing
about humans was innate now both of
those positions are actually rather
extreme if you stop to think about it
for a second you’ll realize that
sometimes when nature and nurture when
DNA and experience fight the winner is
really easy to predict for instance you
can wish all you want for six fingers if
you are not born with six fingers you
will never have them I’m really sorry to
disappoint you on the other hand just
because you cannot speak German today
there is nothing in your DNA at all that
says that you cannot learn it if you
start studying it tomorrow
so yes sometimes the questions can are
easy to answer sometimes those are
simple answers but simple answers are
though they are really really tempting
or most of the time not right
and in fact complex problems are far
more common and to me far more
interesting than simple ones so I want
to tell you a story about my doctoral
work so when I was a graduate student
I’m a human evolutionary geneticist and
what that means is like that I’m really
interested in something what bits of our
DNA make us human and that it and how
they do so and when I was a graduate
student I focused on this bit of DNA
here and why this one well it’s clearly
not very obvious from the sequence and
in fact the reason is something you
might not expect at all because the
reason is milk that’s right
milk so milk is a really complex
substance it contains all kinds of
things but the one I’m really interested
in is this molecule here called lactose
lactose is a sugar just like the glucose
that your doctor tells you and your
parents and your grandparents to keep an
eye out so you don’t get diabetes or
like the fructose that makes fruits
taste sweet but lactose has phone almost
exclusively in milk when you drink milk
it makes its way down your gut into your
stomach
where your body recognizes it breaks it
down and uses it to make energy to fuel
itself and you might remember from
school that our mammals from seals to
pigs to lions they all make milk to feed
their babies and in fact baby sheep baby
gorillas baby sea otters they all rely
on their mothers to nourish them with
milk at the beginning of life but
something happens to all of these
adorable animals when they grow up under
you and that is that they lose the
ability to digest lactose they can no
longer break it down even kittens so you
can feed an adorable kitten a saucer of
milk he will of course drink it and lap
it up and he will be the happiest kid
thing you’ve ever seen probably but if
you feel a grown car a saucer of milk he
might drink it yes in fact I can tell
you they will drink it but believe me
when I tell you they’re not digesting
that lactose they are not breaking it
down I have cats at home so again
believe me when I tell you that I have
seen and I have smelled and I have
cleaned up proof
the fact that they are not digesting the
lactose the only exception to this is
some but this is extremely important not
all humans so I am NOT a child I hope
you will agree although I can on the
less digest lactose very comfortably but
because we are in Singapore I feel
really comfortable saying that the vast
majority of you in this audience could
not go home right now drink a pint of
milk and not feel terrible for a while
that’s it if you don’t believe me if you
haven’t done this experiment please by
all means do it but don’t just drink oh
you know a little sip of milk or a
little pod of yogurt no no no no I want
you to go home and pour yourself a nice
tall glass of just plain cold milk nice
and full of lactose and my guess is that
you’re all gonna end up pretty annoyed
at me for having talked you into doing
that but you know how do I know this I
mean my job is not actually to go around
and ask animals how much they like milk
and I don’t know any of you so I really
don’t know if you like milk but how so
how am I so comfortable in my guess well
the answer is really simple
it’s that bit of DNA that I showed you
in fact it’s that little see the one in
red there that is something that I have
that most of you don’t and that’s
because it’s from primarily in people of
European descent you can see here in
this map which I took from some
colleagues new bunny telling his friends
where that little sea is most common in
popular in places like Britain and
Northern Europe and where it is least
common in the world which is pretty much
anywhere in blue you can also see that
it’s pretty much unseen east of India
which is the region I studied as a PhD
student that single see that tiny little
change gives me the ability to digest
digest lactose as an adult so on the
surface that would seem like a really
clear case for lactose or DNA winning
everything for DNA beating nurture again
right I mean a single difference and I
can do something you cannot you have
them so I have the mutation I can digest
lactose you don’t have it
you feel sick he’s closed right I mean
purely but actually let’s take a step
back because there is one thing missing
from this story that’s the milk where
does the milk come from you know that
bit is certainly not encoded by that
little C so the truth is yes I have a
mutation in my DNA that lets me digest
lactose if I don’t have access to cows
or to goat or to sheep or to camels or
to any other animal we can milk that
mutation is totally pointless being able
to digest milk is a totally pointless
ability if you have no access to milk
so maybe DNA is actually not that mighty
and let me give you another example this
one is a bit more somber but I think
you’ll see what I’m what I mean
so here on this figure you can see on
this graph you can see how common it was
for American men to die of different
types of cancer at different times in
the 20th century and I took this from a
study from the Cleveland Clinic in the
u.s. so the stats are for you u.s. men
as you can see most of the 20th century
the most common form of cancer has been
lung cancer which is the one that I’m
pointing to with a big red arrow over
cancer is a disease that is caused
fundamentally by damage to your DNA that
damages your body’s abilities to control
when and where your cells divide so in a
sense cancer is caused by your DNA so
here we are again DNA genetic destiny
but actually is that really true because
we all know that there is a recent
cancer has become so common in the past
50 60 70 years and it’s got nothing at
all to do with DNA what I’m talking
about of course is the rise of smoking
in fact if you look at the figure you’ll
see that lung cancer was pretty uncommon
in the u.s. until cigarettes became
widespread and while not everybody who
smokes
will get lung cancer and not everybody
who gets lung cancer is a smoker the
fact remains that smoking dramatically
damages the cells in your lungs and that
in turn dramatically increases your
chance
of getting cancer so then what causes
lung cancer is it nature is it DNA I
mean if we damage DNA we get cancer
maybe it’s actually nurture I mean
without smoking without damage to your
genes there is no cancer so if you don’t
smoke you don’t damage your genes you
don’t get cancer
so perhaps you see though where I’m
going with this because my question to
you today is actually well does this
really have to be a fight do we really
need to think of this as nature versus
nurture nature or nurture I think it’s
really really clear that actually it’s
nature and nurture because the truth is
that yes you have genes we all have
genes and these genes do all kinds of
things right but if you look at a single
gene what it tends to do tends to be
pretty small a single gene might do
something like make a protein that
breaks down lactose and in isolation
that’s not really striking you might say
to yourself that’s a fair criticism but
the beauty of the system is that genes
respond to each other a gene can react
to the product of another gene but even
more striking is the fact that genes not
only respond to each other they respond
to other things as well they respond to
the environment in which you live they
respond to the food you eat they respond
to the decisions you make well it’s
really really tempting to have a simple
answer to have some yes or no nature or
nurture
you might also even want someone to
blame in some situations the truces life
is quite messy that’s not how life works
life is really complicated so the next
time you see science you see a newspaper
headline that says Oh scientists have
discovered the gene for cancer again
please keep in mind that what that
article really means is that scientists
have discovered a gene for cancer that
is associated perhaps with higher
likelihood or even less likelihood of
getting cancer in a given environment
because the truth is there is no single
gene for cancer there are many genes
always many genes that control yes your
likelihood of getting cancer but also
things like your height your weight the
shape of your face the color of your
skin even the lightly
of you suffering from major depression
at some point in your life okay but
without the wrong environment likelihood
and chances is all they will ever be and
so I want to leave you with this final
thought despite what you might have
heard before you are not the
battleground upon which nature and
nurture fight no no no absolutely not
you are the canvas upon which they
collaborate you are the product of their
interactions [Applause]