Now all of those findings rely
on being able to compare the experimental population to the control population.
If Dmitry Belyaev had not, in the very beginning, the foresight
to have the control population, we wouldn't know if the selection for
friendliness and aggression actually caused the changes that we're seeing.
It could be that you see curly tails and floppy ears and
all these other things because the foxes lived in cages or
because where they lived or what they ate.
But we know because the control line was kept in absolutely identical conditions.
That it had to be the selection against aggression and interest that caused
the morphological changes, even though they were only selecting for behavior.
That's amazing.
So they also, when they measured the physiology of the experimental foxes.
They found that the serotonergic system had changed In the experimental line
versus control, the serotonin is actually higher in the experimental line.
And that is basically a way to sort of put a break on risky behavior or
aggressive behavior.
And the corticosteroid response to stress is much lower in the experimental line,
so your adrenal glands are on top of your kidneys, and they produce
things like cortisol which is associated with the fight or flight response.
And that was down regulated.
It was reduced in the experimental foxes, relative to the control.
So not only do you see morphological changes, but
you see physiological changes that are involved with aggression and stress, and
finally of course you saw a lot of behavioral changes.
But the neat thing is, the behavioral changes weren't just things that they have
selected for, like approaching and being friendly.
It was things like tail wagging and barking and crying into adulthood.
And so there's much higher levels of barking, and crying, and
tail wagging in the experimental line than in the control population.
And having worked with these foxes,
I can tell you that they are absolutely adorable.
Because when you see them, they cry and whine, and they really,
really want you to come touch them and interact with them.
Whereas the control line that has not been bread for this,
they tend to sort of stay away and not want to approach.
And they certainly don't bark and cry if you don't touch them.
So it's incredible that they selected for one thing.
They selected for interest in humans and
approach behavior, and you get all these changes.
This has huge impact on how we think about how evolution actually works.
Remember, evolution being a change in allele frequency over time, but
it It means that genes are busy.
They do multiple things, and the genes that must have changed in the population,
the allele frequency that changed in the population to cause a reduction and
aggression towards people, and also interest and approach towards people.
They also must be involved in producing the morphological traits and
the physiological traits that we see also change.
So there are accidental byproducts of selection against aggression
that tend to show up again and again, and that's what's suggested by the foxes.
Because it's obviously not just the foxes that have floppy ears.
It's all sorts of domesticated animals.
It's not just the foxes that have curly tales, or
piebald coats, or the star mutation.
And so really what the implications of the fox experiment is that
Dimitri Balaif had discovered what domestication is.
If you want to define it very quickly, domestication is selection against
aggression and it is selection for interest In people and
the willingness and even desire to be with people.
