So it all came to life
in a dark bar in Madrid.
I encountered my colleague from McGill, Michael Meaney.
And we were drinking a few beers,
and like scientists do,
he told me about his work.
And he told me that he is interested
in how mother rats
lick their pups
after they were born.
And I was sitting there and saying,
this is where my tax dollars are wasted,
on this kind of soft science.
And started telling me
that when the rats, like humans,
lick their pups in very different ways.
Some mothers do a lot of that,
some mothers do very little,
and most are in between.
But what's interesting about it
is when he follows these pups when they become adults,
like years in human life,
long after their mother died,
they are completely different animals.
The animals that were licked and groomed heavily,
the high licking and grooming,
are not stressed.
They have different sexual behavior.
They have a different way of living
than those that were not treated
as intensively by their mothers.
So then I was thinking to myself,
is this magic?
How does this work?
Us geneticists would like you to think
perhaps the mother had the bad mother gene
that caused her pups to be stressful,
and then it was passed from generation to generation.
It's all determined by genetics.
Or is it possible that something else
is going on?
So in rats we can ask this question
and answer it.
So what we did is a cross-fostering experiment.
You essentially separate the litter,
the babies of this rat, at birth,
to two kinds of fostering mothers,
not the real mothers,
but mothers that will take care of them,
high-licking mothers and low-licking mothers.
And you can do the opposite with the low-licking pups.
And the remarkable answer was,
it wasn't important
what the gene you got from your mother.
It was not the biological mother that defined this property
of these rats.
It is the mother that took care of the pups.
So how can this work?
I am an a epigeneticist.
I am interested
in how genes are marked by a chemical mark
during embryogenesis, during the time we're in the womb of our mothers,
and decide which gene will be expressed
in what tissue.
Different genes are expressed in the brain than in the liver and the eye.
And we thought, is it possible
that the mother is somehow
reprogramming the gene of her offspring
through her behavior?
And we spent 10 years,
and we found that there is a cascade of biochemical events
by which the licking and grooming of the mother, the care of the mother
is translated to biochemical signals
that go into the nucleus and into the DNA
and program it differently.
So now the animal can prepare itself for life.
Is life going to be harsh?
Is there going to be a lot of food?
Are there going to be a lot of cats and snakes around,
or will I live in an upper class neighborhood
where all I have to do is behave well and proper
and that will gain me social acceptance?
And now one can think about how important that process can be
for our lives.
We inherit our DNA from our ancestors.
The DNA is old.
It evolved during evolution.
But it doesn't tell us if you are going to be born in Stockholm,
where the days are long in the summer and short in the winter,
or in Ecuador, where equal number of hours for day and night
all year round.
And that has such an enormous amount on our physiology.
So what we suggest is perhaps what happens early in life,
those signals that come through the mother
tell the child
what kind of social world you're going to be living in.
It will be harsh, and you'd better be anxious and be stressful,
or it's going to be an easy world, and you have to be different.
Is it going to be a world with a lot of light or little light?
Is it going to be a world with a lot of food or little food?
If there's no food around,
you'd better develop your brain to binge whenever you see a meal,
or store every piece of food that you have as fat.
So this is good.
Evolution has selected this
to allow our fixed, old DNA
to function in a dynamic way
in new environments.
But sometimes things can go wrong.
For example, if you're born to a poor family,
and the signals are, "You'd better binge.
You'd better eat every piece of food you're going to encounter."
But now we humans and our brain have evolved,
have changed evolution even faster.
Now you can buy a McDonald's
for one dollar.
And therefore, the preparation
that we had
by our mothers
is turning to be maladaptive.
The same preparation that was supposed to protect us
from hunger and famine
is going to cause obesity,
cardiovascular problems, and metabolic disease.
So this concept that genes could be marked by our experience,
and especially the early life experience,
can provide us a unifying explanation
of both health and disease.
But is true only for rats?
The problem is, we cannot test this in humans,
because ethically, we cannot administer child adversity
in a random way.
So if a poor child develops a certain property,
we don't know whether this is caused
by poverty
or whether poor people have bad genes.
So geneticists will try to tell you that poor people are poor
because their genes make them poor.
Epigeneticists will tell you
poor people are in a bad environment or an impoverished environment
that creates that phenotype, that property.
So we moved to look
into our cousins, the monkeys.
My colleague Steven Soomey