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High school biology - NGSS
Course: High school biology - NGSS > Unit 8
Lesson 3: Species and the environmentSpecies and the environment
Changes in the physical environment, whether naturally occurring or human induced, have contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline–and sometimes the extinction–of some species. Created by Sal Khan.
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Video transcript
- [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.