Animal Behavior – CrashCourse Biology #25

Behavior is action in
response to a stimulus. My cat Cameo is now responding
to both an external stimulus the sound of a bag of treats,
and an internal stimulus her hunger, or at least her
insatiable desire for treats. Sometimes animal behavior
can seem really far out, but if you look closely enough, you can see how all
behavior serves a purpose to help an animal mate, eat,
avoid predators, and raise young. And since behaviors can come
with advantages like these, natural selection acts on them
just as it acts on physical traits ensuring the success
of animals who engage in beneficial behaviors, while
weeding out those that do stupid, dangerous or otherwise
unhelpful stuff. The most beneficial behaviors
are those that make an animal better at doing the only two
things in the world that matter: eating and sex. Still, that doesn’t mean
all behavior is about just looking out for number one. It turns out some
advantageous behavior is actually pretty selfless. More on that in a minute. But first, behavior is really just
a product of a pair of factors: Morphology, or the physical
structure of an animal and physiology, or the
function of that morphology. Now, an animal’s behavior
is obviously limited by what its body
is capable of doing for example, Cameo does
not have opposable thumbs, so, much as she would like
to get into the treat bag, by herself, she cannot. This limitation is
strictly hereditary no cats can open treat
bags with their thumbs because no cats
have opposable thumbs. Though some cats do have thumbs. In the same way that a penguin
can’t fly to escape a predator; or a gazelle can’t reach the
same leaves as a giraffe can. Similarly, behavior is constrained
by an animal’s physiology. Like, Cameo’s built for
chasing down little critters and eating meat,
not beds of lettuce. This is because her physiology,
everything from her teeth to her digestive system,
are geared for eating meat. If she pounced on and ate every
blade of grass she came across… let’s just say I would not want
to be in charge of that litter box. Now the traits that make
up an animal’s morphology and physiology are
often heritable, so we generally talk about
selection acting on those traits. But as natural selection
hones these traits, it’s really selecting
their associated behaviors. It’s the USE of the trait, using wings and feathers
to escape predators, or using a long neck
to reach leaves, that provides the
evolutionary advantage. Still, that doesn’t mean
all behavior is coded in an animal’s genes some behaviors are learned. And even for animals that
learn how to do things, natural selection has
favored brain structures that are capable of learning. So one way or another, most behaviors have
some genetic underpinning, and we call those
behaviors adaptive. Problem is, it’s
not always obvious what the evolutionary advantages
are for some of the nutty things that animals do. Like, why does a snapping turtle
always stick out its tongue? How does a tiny Siberian
hamster find its mate, miles across the
unforgiving tundra? Why does a bower bird
collect piles of garbage? To answer questions like those, we have to figure out what
stimulus causes these behaviors, and what functions
the behaviors serve. To do this, I’m going to need
the help of one of the first animal behavior scientists ever,
or ethologists, Niko Tinbergen. Tinbergen developed a
set of four questions aimed at understanding
animal behavior. The questions focus on
how a behavior occurs, and why natural selection has
favored this particular behavior. Determining how a behavior occurs
actually involves two questions: One: what stimulus causes it? And two: what does
the animal’s body do in response to that stimulus? These are the causes
that are closest to the specific behavior
we’re looking at, so they’re called
the proximate causes. In the case of the
male Siberian hamster, the stimulus is a delicious
smelling pheromone that the sexy female hamster
releases when she’s ready to mate. The male hamster’s response,
of course, is to scuttle, surprisingly quickly, over
several miles if necessary to find and mate with her. So the proximate cause
of this behavior was that the girl hamster signaled
that she was ready to knock boots, and the male ran like crazy
to get to the boot-knockin’. Asking the more complex question
of why natural selection has favored this behavior requires
asking two more questions: One: what about this behavior
helps this animal survive and/or reproduce? And two: what is the evolutionary
history of this behavior? These, as you can tell,
are bigger-picture questions, and they show us the ultimate
causes of the behavior. The answer to the first
question, of course, is that the ability of a male
hamster to detect and respond to the pheromones of an ovulating
female is directly linked to his reproductive success! As for the second question, you
can also see that male hamsters with superior pheromone detectors
will be able to find females more successfully than
other male hamsters, and thereby produce more offspring. So natural selection has honed
this particular physical ability and behavior over
generations of hamsters. So, who would have thought to ask
these questions in the first place? And where’s my chair? Niko Tinbergen was
one third of a trifecta of revolutionary ethologists
in the 20th century. Along with Austrians Karl
von Frisch and Konrad Lorenz, he provided a foundation
for studying animal behavior and applied these ideas to
the study of specific behaviors and for that all three shared
the Nobel Prize in 1973. You may have seen the famous
photos of young graylag geese following obediently
in a line behind a man. That was Lorenz,
and his experiments first conducted in the 1930s
introduced the world to imprinting, the formation of social
bonds in infant animals, and the behavior that includes both
learned and innate components. When he observed newly
hatched ducklings and geese, he discovered that
waterfowl in particular had no innate recognition
of their mothers. In the case of graylag geese,
he found the imprinting stimulus to be any nearby object
moving away from the young! So when incubator-hatched
goslings spent their first hours with Lorenz, not only did they follow him, but they showed no recognition
of their real mother or other adults in their species! Unfortunately, Lorenz was
also a member of the Nazi party from 1938 to 1943. And in response to
some of his studies on degenerative features
that arose in hybrid geese, Lorenz warned that it
took only a small amount of “tainted blood” to have an
influence on a “pure-blooded” race. Unsurprisingly, Nazi party
leaders were quick to draw some insane conclusions from
Lorenz’s behavioral studies in the cause of what
they called race hygiene. Lorenz never denied
his Nazi affiliation but spent years trying to
distance himself from the party and apologizing for getting
caught up in that evil. Now how exactly does
natural selection act on behavior out
there in the world? That’s where we turn to
those two types of behavior that are the only things
in the world that matter: eating and sex-having. Behavior associated with
finding and eating food is known as foraging,
which you’ve heard of, and natural selection can act
on behaviors that allow animals to exploit food sources while using the least
amount of energy possible this sweet spot is known as
the optimal foraging model. And the alligator snapping
turtle has optimal foraging all figured out. Rather than running around
hunting down its prey, it simply sits in the water,
and food comes to him. See, the alligator snapping
turtle has a long, pink tongue divided into two segments,
making it look like a tasty worm to a passing fish. In response to the stimulus
of a passing fish, it sticks out its tongue
out and wiggles it. Natural selection has,
over many generations, acted not only on turtles with
pinker and more wiggly tongues to catch more fish, it’s also
acted on those that best know how and when to wiggle those
tongues to get the most food. So it’s selecting
both the physical trait and the behavior that
best exploits it. And what could be sexier than
a turtle’s wiggly tongue dance? Well, how about sex? As we saw with our friend
the horny Siberian hamster, some behaviors and their
associated physical features are adapted to allow an
animal to reproduce more, simply by being better
at finding mates. But many times, animals of the
same species live close together or in groups, and determining
who in what group gets to mate creates some interesting
behaviors and features. This is what sexual
selection, is all about. Often, males of a species will
find and defend a desirable habitat to raise young in, and
females will choose a male based on their territory. But what about those species,
and there are many of them, where the female picks a
male not because of that, but because of how he
dances, or even weirder, how much junk he’s collected? Take the male bower bird. He builds an elaborate hut,
or bower, out of twigs and bits of grass, then spends
an enormous amount of time collecting stuff, sometimes
piles of berries, and sometimes piles of
pretty, blue, plastic crap. Ethologists believe that
he’s collecting the stuff to attract the female to check
out his elaborate house. Once the female’s been
enticed to take a closer look, the male starts to sing
songs and dance around, often mimicking other species,
inside of his little house for her. Females will inspect
a number of these bowers before choosing who to mate with. Now, doing more complex dances
and having more blue objects in your bower scores
bigger with females. And ethologists have shown that
a higher level of problem solving, or intelligence,
in males correlates to both of these activities. So yeah, it took some
brawn to build that bower and collect all that junk,
but chicks also dig nerds who can learn dances! So the bowerbird’s brain
is evolving in response to sexual selection by females. This intelligence
likely also translates into other helpful behaviors
like avoiding predators. So thanks to the
evolution of behavior, we’re really good at taking care of
our nutritional and sexual needs. But what’s confused
scientists for a long time is why animals often
look after others’ needs. For instance, vampire bats
in South America will literally regurgitate blood into the
mouths of members of its clan who didn’t get a meal that night. How do you explain animals who
act altruistically like that? We actually did a whole SciShow
episode on this very subject but basically, we can thank British
scientist William Hamilton for coming up with an equation to
explain how natural selection can simultaneously make
animals fit and allow for the evolution of altruism. Hamilton found that the
evolution of altruism was best understood at the
level of larger communities, especially extended
animal families. Basically, altruism can evolve
if the benefit of a behavior is greater than its
cost on an individual, because it helped the
individual’s relatives enough to make it worth it. Hamilton called this
inclusive fitness, expanding Darwin’s
definition of fitness basically, how many
babies somebody’s making to include the
offspring of relatives. So I guess the only
question left is, if I forget to feed you two, who is going to regurgitate blood
into the other one’s mouth? Yeah, there’s probably a reason
that only happens with bats. Thank you for watching this episode
of Crash Course Biology. Thank you to Cameo for
being such a good kitty. Yeah, she finally gets her treats. There’s a table of
contents, of course. If you want to reinforce any of the
knowledge that you gained today. If you have questions or ideas
for us you can get in touch with us on Facebook or Twitter, or
of course, in the comments below. We’ll see you next time.


  1. shaun03a May 4, 2018 at 1:45 am

    Horny Siberian Hamster sounds like a killer band name.

  2. Orrin Rempel May 16, 2018 at 12:07 am


  3. Wilber Castillovillatoro May 16, 2018 at 12:37 pm


  4. Wilber Castillovillatoro May 16, 2018 at 12:38 pm


  5. Wilber Castillovillatoro May 16, 2018 at 12:38 pm


  6. Wilber Castillovillatoro May 16, 2018 at 12:38 pm


  7. Wilber Castillovillatoro May 16, 2018 at 12:38 pm


  8. Zharth May 19, 2018 at 11:34 am

    I hate to bring this up even, but it seems that Altruism is pinnacle argument against Jordan Peterson's claims of scripture being responsible for humans to acquire a level of morality that exists today. He literally brushes off the idea of other animals behaving a specific way for benefit of its' community/survival as "lower than consciousness", and that it's not the same. It's perfectly reasonable to hypothesize that humans simply achieved a point of self-awareness from the evolution of complex communication, and rationalized that it would be smarter to get into bigger and bigger tribes in order to completely dominate the playing field. You don't get to where we are by not respecting that natural guideline of depending on others to survive easier. After all, almost every primate species has adopted grouping properties, long before we were here. It's possible that scripture played a role in influencing it in a more strict manor in attempt to abolish the idea of death itself, but it certainly isn't to credit for why we've won the battle of natural selection vs. the animal kingdom. We now play against our own species obviously.

    This video was really insightful, thank you.

  9. Megan Rivera June 7, 2018 at 7:32 am

    Plz tell cameo that I love her

  10. Marilyn Hellmuth June 21, 2018 at 12:25 am

    That’s so gross!

  11. Ui Ytresen July 4, 2018 at 11:27 am

    Bower birds?
    wait for it … BECKY, LEMME SMASH!

  12. Hana H July 12, 2018 at 6:57 am

    can we have more videos with the cat in frame pls she helps me focus

  13. Patricia McGeorge August 9, 2018 at 10:01 am

    I am a linguist and have come to take our technical terms back. How dare you biologists steal our morphologies you analytical polysynthetic labiodental fricatives!

  14. roberto almeida August 16, 2018 at 7:28 pm

    I thought he was going to say "How much junk he has" 8:08

  15. Martin Betancurt September 28, 2018 at 2:43 pm

    Subtítulos en español por favor!!!!!!!

  16. jourdan p October 16, 2018 at 6:17 pm

    Ahh, you talk so fast. Hard to keep up. But good info!

  17. Jansen Huang October 22, 2018 at 11:51 pm

    Notice his neck? Might be scratched LOL

  18. Sharp Design November 15, 2018 at 6:14 pm

    was not expecting to learn about hamster boot-knockin' today. interesting.

  19. gamin star November 26, 2018 at 4:22 pm


  20. Brandon Park December 3, 2018 at 5:30 am


  21. Brittani Hylton December 10, 2018 at 2:55 am

    l'm curious about the book you are reading in this video. I tried looking it up but I was unable to find it.

  22. Nabeeha Khaled December 17, 2018 at 7:51 pm

    Cameo made a cameo!

  23. David Nzekwu January 7, 2019 at 3:36 pm

    thank u

  24. Anika Greene February 20, 2019 at 1:41 pm


  25. Pari Ramchandani February 22, 2019 at 8:07 pm

    u talk too fast

  26. Deacon Gibbs February 27, 2019 at 4:20 pm

    W8 what if deadpool is a super sponge…

  27. Melis W March 9, 2019 at 8:43 am

    My cats reacted to the treat bag sound when they heard it on the video!

  28. THEOFILOS CHALDEZOS May 11, 2019 at 2:06 pm

    Behaviorism vs ethology video?

  29. harys_john May 13, 2019 at 7:21 pm

    8:35 We should train that bird to dance like Ricardo, that behaviour will quickly be selected for throughout the species xD

  30. Kyle Hagerty May 19, 2019 at 9:04 pm

    But my cat just rips the treat bag open

  31. S Kim May 24, 2019 at 10:57 am

    If eating and sexing are the two most important things in the world, what are the reasons for wolves to follow and obey their alpha? Is it because they might get the food if they belong to a group and follow the rules?

  32. margaux susman May 28, 2019 at 9:38 am

    The references link doesn't work.

  33. ty gje June 24, 2019 at 10:14 pm

    Pet the doggg for Christ sake

  34. john tindell August 10, 2019 at 7:51 am

    Thank youuuuu

  35. Lucas August 21, 2019 at 12:37 pm


  36. Chastelle Bennett September 4, 2019 at 1:50 am

    Wow hank I’m sorry but your cat is fat.

  37. Evan Palmer September 17, 2019 at 2:30 am


  38. Kevin Gruen September 25, 2019 at 4:58 am

    What does this guy not know?

  39. Kay W September 29, 2019 at 10:12 pm


  40. Samantha Hiserote October 4, 2019 at 11:58 pm

    Becky does not, in fact, want to smash.

  41. Cordless October 22, 2019 at 5:21 pm

    1:12 Can we just accept the fact that the dog simply looks depressed

  42. Wi _VERSA November 12, 2019 at 8:19 am

    This needs to be redo

  43. andrew sutherland December 19, 2019 at 3:42 pm

    Altruism is a quality of slytherins

Leave a Comment

Your email address will not be published. Required fields are marked *