 
 
 
 
Hi. It's Mr. Andersen and welcome
to Biology Essentials video number 26. This
is on behavior. And how behavior effects natural
selection. This is a picture of Charles Darwin.
It think he's about 50 years old in this picture.
He seems to just be thinking. And he did a
lot of that. This is at his house at Down,
his thinking path. And so what he would do
is he would put some rocks here in a pile
and then he would walk around. And every time
he walked by he would kick another rock out
of the way as a way to kind of count the number
of times he's walked around the thinking path.
And so Darwin thought a lot. And in fact when
you read the Origin of the Species, it's a
lot of mental arguments. But there's no genes
and there's not any math really to back it
up. And so Darwin was right, but he also didn't
measure natural selection. In other words,
there were at the time he was walking around
this path that whole peppered moth with the
white color and dark color was going in England.
And if he would have actually been measuring,
which nobody else was at that point, he could
have gotten some data to back up his theories.
And today we measure natural selection everywhere.
Not only in the beaks of the finches in the
Galapagos, but in the guppies of South America.
And in the viruses of HIV. We measure it everywhere.
And so what I'm going to try to do in this
video is talk about four types of behavior
and how they would affect natural selection.
Remember behavior, it's how you act, can either
be innate or it can be learned. Innate means
you're born with it. And so it's in your genes.
Learned means you pick it up during your lifetime.
And so a chimpanzee that learns from its mother
how to use a tool would be a learned behavior.
However that grabbing reflex in a baby chimpanzee,
holding on to its mom is innate. And so what
we're going to look at is behavior in organisms
and how they affect natural selection. The
two plant ones we'll talking about are phototropism
and then photoperiodism. This is growth towards
or away from light. And then growth and response
to the amount of light. We'll talk about courtship
in animals. An example will be the bowerbird.
And then finally we'll talk about how organisms
can cooperate. Example we'll do insects and
flowers and how they coordinate their efforts
in symbiosis through pollination. And so let's
start with phototropism. Now first of all
we should define what it is. Phototropism
is growing in response to light. And so if
the light is over here you can actually see
it in this picture, if the light is coming
over here, remember what happens in a plant
is that the auxin will move away from the
light. That makes the cells on this side of
the plant grow faster than the cells on this
side. And so it'll kind of bend in that direction.
Phototropism is growth towards light. It could
be growth straight up. It could be growth
at an angle. All of this is phototropism.
Now how does this apply to natural selection?
Well when you look at a forest, like a rain
forest like this, you think it's very pretty.
But it's really like war. There's a war going
on between all the plants in this forest and
it's a light war. They're trying to get as
much light as they can. And for all the trees
that you see, there are a number trees that
you don't see. And that means that they don't
get light. And that means that they die and
they're genes die with them. In other words,
how did phototropism come to be? Well it could
be that auxin was used for another purpose.
Just to get plants to grow but once you had
differential movement of oxygen, auxin, excuse
me, they you could get growth in response
to light. And so if you can't grow towards
light you die and the genes would die with
you. But it's being tweaked on a daily basis.
What about photoperiodism? Photoperiodism
is responding to the amount of light during
the day. And so we can sense climate, or excuse
me, weather with that. And so this is a rose.
And it's a rose that's flowering. It's trying
to attract pollinators. But it has a choice
to make. This plant had to, and when I say
that I'm anthropomorphizing a little bit,
it has been decided at what time it actually
will flower. And what decided that was natural
selection. So you imagine, let's say we have
a bunch of roses and some flower way early
in May. And some flower in June. And some
flower in July. Well, if you flower too early,
winter comes late, and the rose may die. So
it won't, even though it's flowered early
and grown early, you can't pass that off because
maybe there's no insects to actually pollinate
it. Or maybe it physically dies. Now July,
we don't think of July being a time to winter.
So how could they die here? Well let's say
you flower late, that means you drop the seeds
late. That means winter comes and kills them
earlier. Or you don't have time to actually
drop the seeds. And so there's this bell shaped
curve of a perfect time to flower. They're
sensing the photoperiodism using phytochromes
and figuring out this is the time to flower.
And so that's been chosen over time. What
time they flower. You flower too early it
doesn't work. Flower too late. But as the
climate starts to change, we're probably starting
to see a shift of this bell shaped curve towards
May. Okay. Let's talk about courtship. Courtship
in humans, you're probably familiar with,
but courtship in all animals is super important.
And that's due to sexual selection. So this
is a bowerbird. A bowerbird get's its name
because it builds a bower. A bower's like
a house. And this is a male bowerbird. And
it literally has built this whole bower. This
is in Australia. It's a greater bowerbird.
So it's lined up these leaves in here. It's
lined up all of the rocks and these sticks
and the leaves are positioned here. In other
words this bowerbird has made this attractive
to attract a female. So she'll actually fly
around, the female bowerbirds, looking for
the best bower. And she's going to choose
to only mate with a male that can make like
a super nice bower. It's similar to a guy
with a very fancy car. A very fancy house.
Trying to impress a female. Why is that? Well
if you are a male bowerbird that can build
this beautiful bower, that probably means
that you have a brain that works correctly.
An that probably means that your DNA is intact.
And so it's a really good judge of your fitness.
And so females that chose males that could
make a really good bower were more likely
to have offspring and pass those genes on.
If you had a really messy bower, as a male,
you didn't pass your genes on. As a result
that's been eliminated as well. So natural
selection at play. In this case it's probably
mostly sexual selection. And then finally
I want to talk about cooperation and pollination.
Cooperation shows what's called coevolution.
In other words, once flowers started flowering,
insects started trying to eat the flowers.
And initially probably that was a parasitic
relationship. In other words insects were
trying to feed on the flowers. Plants figured
out. And what I mean by figured out is maybe
some of those insects actually, while feeding
on plants, transferred the pollen from one
organism to another. And eventually we had
this coevolution where the evolution of the
flower and the evolution of the insects are
inexorably linked together. If we have decrease
in bee populations now, what's going to happen
to the flowers? Well maybe they'll have to
evolve back to a wind or some other way of
distributing their pollen. And this cycles
back to Darwin again. So Darwin understood
natural selection. Understood all of this.
Unfortunately, didn't study it. Didn't actually
measure these things. But he was looking in
Madagascar. I don't think he went, he could
of gone, I'm not sure if he went there or
not, but was looking at Darwin's orchid. It's
named after Darwin, after that. But the cool
thing about it is that it's got about a foot
long distance from the outside of the flower
down to the bottom where the nectar is found.
And so Darwin saw this orchid and he predicted
that in the future they'll find some kind
of an insect or something that has a really
long proboscis. And what they found was this
moth. This moth has a proboscis that normally
is in a butterfly or any moth or stuff like
that it will actually wad up like that when
they're flying around. But it will unwind
and so it can get to the nectar inside it.
And we call this xanthopan morganii praedicta.
And the praedicta means that it was Darwin's
prediction that it would, they would have
that length. And so this is coevolution between
these organisms. But essentially the behavior
that you have determines if you survive or
die. And that leads to natural selection and
eventually adaptation of the organisms. And
so I hope that's helpful.
