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by being one of the first 200 people to sign up at brilliant.org/HAI. Much like vampires, babies, and this intro,
mosquitos suck. Let’s get started. So, the London Underground
is an English public transit system whose ubiquitous “Mind the Gap” motto is the
third most annoying MTG. But perhaps their motto should instead be
“Mind the Trap,” because the whole thing is basically a flytrap, except that you’re
the bait and instead of catching flies, it just like has a lot of flies and they’re
actually not flies, they’re mosquitos and you know what this is taking too long. So, for years there were urban myths throughout
London about vicious mosquitos who lived in the Underground and loved biting humans almost
as much as Mike Tyson. The rumors started out among Underground workers,
but soon spread far and wide among blokes, lads, birds and sods when Brits had to take
shelter in the Underground’s tunnels during the Bombing of London during World War II:
War Harder. But, it turns out that unlike widely debunked
urban myths like Bigfoot or Australia existing or the HAI and Wendover guy being the same
guy, this one was actually true. In the late 1990s, some lame nerds did some
lame nerd stuff and determined that the London Underground is home to a distinct type of
especially bitey mosquitos called culex molestis—a weird name about which there are no jokes
I feel comfortable making. So, why are there strange people-eater skeeters
in the London Underground? Well, while there are a few theories, one
leading hypothesis is that this mosquito actually evolved specifically in the Underground to
adapt to its new surroundings. When the underground tunnels were built and
then sealed off in the 1860s, some mosquitos got trapped underneath—but instead of dying,
they decided to not die and developed underground-favoring characteristics. Unlike the typical surface mosquito, culex
pipiens, culex molestis don’t hibernate in winter, can mate in small spaces, don’t
need what’s called a blood meal—one of the grossest terms to date in HAI history—in
order to reproduce, and primarily feed on mammals like rats and humans as opposed to
birds. Now, are culex molestis actually a new species? Well, a bunch of the science jerks have a
bunch of various science jerk opinions about that, because apparently changing species
is a lot more complicated than Animorphs led me to believe, but studies have generally
found that the underground mosquitos very rarely reproduce with surface mosquitos and
when they do, the offspring are usually not fertile, and that’s species enough for my
little smooth brain. Perhaps the more interesting question, though,
is just how the underground mosquitos were able to become so different from the surface
mosquitos so quickly—and to understand that, we have to talk about the three types of natural
selection. To understand how they work, let’s consider
our beloved Half as Interesting mascot, Giraffe as Interesting, who has always been our mascot
and which we totally didn’t make up just now. The first type of natural selection is called
directional selection, and it’s when a species finds that it would benefit from a clear move
in a certain direction, so the entire species begins to shift that way. So, let’s pretend our giraffes live somewhere
that only has really tall trees because of reasons. In that case, that giraffe population is going
to move in the direction of having a longer neck—and that shift, in that one, distinct,
advantageous direction, is directional selection. The second type of natural selection is stabilizing
selection. That’s when a population stabilizes around
a non-extreme trait, because the average is optimal, and variation is disadvantageous. So for our giraffes, let’s say that again
because of reasons, they now live somewhere with trees that are only at a middle height. If a giraffe’s neck is too short, it won’t
be able to reach up to the middle high plants; but if it’s too tall, it won’t be able
to reach down to middle plants, because in this example we’re pretending that the giraffe
can’t bend its neck because look it’s the only way the example works. So, stabilizing selection is going to center
around the average phenotype: giraffes with a middle-height neck. That average will continue to be selected,
and the disadvantageous variations of higher and lower necks will lose out, so over time
the population will shift towards more middle-length necks and fewer variant necks. The third type of natural selection—which
is the rarest, limited-edition collector’s Blu-Ray version—is called disruptive selection,
and it’s what may have happened with our special skeeters. Disruptive selection is when a population
splits in two, because as Malcolm taught us, being in the middle can actually be a disadvantage. So let’s say that, once again thanks to
reasons, our giraffes live in a place with only very short trees and very tall trees. It would be advantageous for the giraffe’s
neck to be either very tall, or very short, and it would be disadvantageous for it to
be a middle length. In that case, you’d likely see the giraffe
species split, with a short necked variant, and a long necked variant, and not a single
middle neck to be found. And that’s basically what the mosquitos
did, except instead of neck length it was gross mosquito stuff about blood meals. Once the underground mosquitos started to
adapt to being underground, any star-crossed pairing of an underground Romeo skeeter and
a surface Juliet skeeter would produce offspring that wasn’t well suited to either the surface
or the underground—which meant that the surface and underground mosquitos quickly
became reproductively isolated, which is the key element in speciation. These mosquitoes are just one buzzy example
of the growing phenomenon of natural selection being shaped by human behavior. Finland’s tawny owl, for example, has long
come in two convenient color options: a brown variety that camouflages in trees, and a grey
variety that camouflages in snow. But as climate change makes Finnish winters
less snowy, grey tawny owl populations have declined, and unlike with the NFL, the Browns
are now dominant. Rising water temperatures have also led to
a genetic shift in some pink salmon, who now migrate earlier in the year, and use of pesticides
has led to bedbugs in New York City that are 250 times more resistant to pesticides, which
finally explains why it’s the city that never sleeps. Evolution shows that little changes can, over
time, have a big impact—and that’s also the best way to learn new things. Brilliant is a website and app that can help
you learn new topics in STEM, which is based on having you learn bit-by-bit, in manageable
chunks. Here at HAI, making these videos involves
learning about new stuff every week, and we know, just like you do, that there’s nothing
more frustrating than trying to learn about something new and getting overwhelmed by a
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leaning method to some quite advanced topics, such as Integral Calculus, Quantum Computing,
or Neural Networks, and so has helped me learn things that I thought were a lost cause after
high school. You can join their community of 8 million
learners, and get started on anything from quantum computing to algebra II for 20% off
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