Richard Dawkins: "How does learned behavior evolve into inherited
instinct?"
Well that's a very advanced question because it wouldn't occur to
many people that that is what happens, but there is a very interesting
theory about how that happens and why it happens.
It's called the Baldwin effect.
In the Baldwin effect, the idea is that an animal learns, for
example, some skill. A good example might be thrushes, which smash the
shells of snails and then eat them. And the closely related blackbirds
don't do this.
If you give a blackbird a snail that's been taken out of its shell,
it's very happy to eat it, but a blackbird hasn't the faintest idea
how to smash a snail, whereas thrushes do it all the time, they do it
on so called anvils.
Now the Baldwin effect idea would be that some ancestral bird,
ancestral to thrushes, learned how to smash snails. A very, perhaps a
very skilled bird, a very clever individual bird that learned how to
smash snails and then maybe other thrush ancestors copied it. They
also learned how to smash snails and got rewarded for it and so they
learned and learned and learned.
And then as the generations went by, the progeny, the next
generation, of these ancestral birds also learned. Perhaps by imitating their parents. And as the generations went by,
the ones who learned fastest, were the ones who got the most
food.
And so any genetic tendency to be fast at learning how to smash
snails would have been favored by natural selection.
And so natural selection, by choosing genes over many generations,
would eventually build into the gene pool a skill which started out as
a learned skill. Now learned skills are very important in
birds.
A beautiful example is the habit of tits, blue tits and grey tits,
of opening milk bottles.
Nowadays not many milk bottles are delivered on doorsteps, but
there was a time when I was young, when every day the milkman would
deliver milk and place it on the doorstep. And grey tits and blue
tits discovered, some individual birds discovered, how to open the
either tinfoil or cardboard tops to these bottles and drink the
cream. Fascinatingly, this habit spread like an epidemic.
Birds copied each other and ornithologists were able to actually
trace the flow of this habit, of this skill, in radiating circles
outwards from focal points in the country in Britain, where
particularly clever individual birds had discovered how to do it. So
it was a learned skill.
As far as I know, nobody has investigated the Baldwin effect in this
particular case, but the way it would work would be that as the
epidemic, the learned habit spread, over generations, those individual
birds who learned fastest were the ones who got the most cream,
therefore had the most offspring, passed on the genes, not initially
genes for opening milk bottles, but genes for learning quickly to open
milk bottles.
And in the end they would learn so fast, they wouldn't need to learn
at all and then you might call it an instinct. And that would be the
full Baldwin effect.
So the Baldwin effect would be a way in which a learned habit can get
built into the gene pool as an instinct by natural selection of genes.
Superficially, the Baldwin effect sounds like Lamarckism.
Lamarck was the French naturalist predating Darwin, who had a theory
of evolution which was based upon the inheritance of acquired
characteristics and that's wrong, that doesn't happen, or almost
certainly doesn't happen. But the Baldwin effect produces something
which looks like Lamarckism and is therefore very
interesting.
Acquired characteristics, something that an animal learns, are not
automatically incorporated in the genes. That would be Lamarckism.
Injuries, uh...
My mother once had a dog, who sometimes, like many small dogs, limped
on three legs. And there was another dog in the village who had lost a
leg in a car accident, and the owner of this three-legged dog thought
that her dog must be the father of our dog, because it limped on three
legs.
That would be Lamarckism. In the case of the thrushes or the tits
that I've just been mentioning, it would be Lamarckism if the learned
habit just was pumped straight into the genes, but the way it happens
is not like that.
The way it happens in the Baldwin effect is that there must be some
genetic variation in there, which affects the rate of learning this
particular habit or even the rate of learning generally, and that is
what's being naturally selected.
So it's not that the habit gets pumped into the genes. What happens
is that there is spontaneous variation among the birds, in proper
Darwinian fashion, ultimately due to mutation; variation in ability to
learn a habit such as this. And then natural selection favors those
individuals who learn fastest, until in the end they learn so fast
that it looks as though they haven't learned at all…
Richard Dawkins Foundation for Reason and Science
