- [Instructor] So we tend to view evolution
and natural selection and the formation of new species,
which is often called speciation,
as a slow process that could take
tens or hundreds of thousands of years,
or, in many cases, millions of years.
And that's why it's always interesting to see examples
of when it might actually be happening
more on a human timeframe.
So this right over here is a picture
of a male Central European blackcap.
So historically Central European blackcaps
would spend their summers in Central Europe
right over here,
in what we would now consider Germany.
So let me write summer right over here.
And then, when it gets colder in Central Europe,
they would migrate and spend their winters in Spain.
So this is where they would spend their winters.
Now, whenever we talk about migratory patterns like this,
it's always interesting to note
that it's not that all of the birds always go
on the exact same migration path.
As we've talked about in many videos,
you tend to have variation in a population.
There are birds that because of genetic differences,
they might go in other directions.
They might go that way, they might go that way,
they might go that way.
But those variants probably weren't successful.
Some of them might end up in the North Sea.
Some of them might end up freezing to death.
Some of them might not be able to have sources of food
while the dominant variant that wintered in Spain
was successful.
It was warmer there.
They had access to food.
Now, this is where it gets interesting.
In the 1960s and 1970s, it became more and more popular
to put backyard bird feeders in England.
And so some of those Central European blackcaps
just happened to go in that direction.
They might've always been happening to go there,
some small percentage of the population,
but those didn't do so well.
But now all of a sudden you had these backyard bird feeders
in England, and so these birds were able
to be quite successful.
They were able to get food.
They were able to thrive.
And so over time, this became a larger and larger proportion
that was able to successfully go in that direction
and then migrate back in the summer and then reproduce.
Now, not only did that gene not get selected against,
and now the birds that had the genes
to go in that direction were thriving,
but they also started mating with each other
more and more frequently
because they would all get back to Germany earlier.
Because when the winter ended,
they had a shorter distance to travel on the way back
than the ones that went to Spain.
And so as they started reproducing with each other
more, and more, and more,
we started to see differences beyond migration direction
in these two groups of Central European blackcaps.
The ones that traveled northwest
started to see rounder wings
versus pointier wings for the ones
that were historically going to Spain.
Well, pointier wings are better for traveling long distances
and rounder wings are more maneuverable,
and if you don't have to travel as long of a distance
that is more desirable.
Now, it's not like these birds knew
that they needed rounder wings.
But once again, even in the pool that was going
to the northwest, you would have had variation,
some pointy wings, some round wings.
But the round wings might've been more successful
so that became a more pronounced trait in that group.
While, similarly, the ones that went to Spain,
some of them might've had rounder wings,
but they might not have been as successful
to get all the way to Spain and back
so the pointier wings, that phenotype, seemed to thrive.
So this is an example how an environmental change,
and here the environmental change is people deciding
to put bird feeders in their backyards in England
in the 1960s and 1970s,
has actually over just the course of roughly
30 or 40 generations began what some biologists
view as a speciation event.
The ones that go northwest can still interbreed
with the ones that go to the southwest.
But over time, if the two groups keep breeding
amongst themselves because of the timing of their migration,
they might not be able to interbreed anymore
and then you would have two different species.
So this is just one example.
There are many other examples about how the physical
environment can contribute to the expansion of some species,
the emergence of new distinct species,
or, in certain situations,
cause a decline in the species
and, in the extreme. an extinction,
which we'll talk about in another video.