- Hi, I want you to
meet my friend Shoshana, she's a zebra finch and
she's very good at it. She's here to help me talk
about comparative anatomy which is the study of
similarities and differences between the anatomies of animals. We study comparative anatomy because it helps us learn more about our evolution and
our shared ancestries. Organisms have their evolutionary history written all over them if
you know what to look for. For instance, which of
these two living organisms would you say I'm more closely related to? Shoshana the finch, or Gordon the plant? This isn't a quiz, but
sure, sure, it is a quiz, it is the easiest quiz that you will ever take in your life. (upbeat music) Well Gordon is green
and can make is own food with just sunlight, water, carbon dioxide, while Shoshana can't make her own food. She has to move around
to find stuff to eat, to escape predators, to find mates, to poop on bark benches, just like me, except not the pooping on park benches, I mean the moving around. So yeah, shocker, I'm more closely related to a bird than to a plant. You get a gold star. So that one's obvious, but as the relationships
between organisms get closer, the questions get a lot more interesting. So what is an animal? I mean I know you know what an animal is, but when you're looking
at Shoshana and me here, what clues you in to the
fact that we are members of the Kingdom Animalia? Two things. For starters, we're both moving. Locomotion is a really good sign that an organism is an animal,
unless you're a sponge. Now I know what you're thinking though, protists, bacteria, and archaea they all move around
using flagella and cilia, but they also only have one cell. It's the multicellular locomotion that's so peculiar and
specific to animals. So animals move because
of the second trait that we have in common,
we're heterotrophs. We get our energy from
eating other lifeforms. Locomotion also helps us avoid predation and seek out mates for reproduction. Now plants, they can mate by dispersing their seed to the wind or having an insect come
by and fertilize them. But if land animals did that, things would get, like
really messy and gross. Some aquatic animals
actually do just release their sex cells into their surroundings and cross their fingers and presumably close their mouths and hope that somebody gets pregnant. So since animals have
to eat and move around they evolved anatomical forms that help them do those things. But obviously those forms
are the same in all animals. For instance, in order
to move Shoshana and I both have to be able to apply force to the ground or the
air to propel ourselves. Here is me pushing off
the ground with my feet. And now here's Shoshana
applying force to the air with her wings which keeps
her afloat and moving. And if I had a shark
in the studio with me, which thankfully I do not, so I'll just pretend to be a shark, my fins would apply force to the water to propel me forward. I have to be careful with this stuff, because even though
similar body structures like fins or wings or feet can mean animals have a
close common ancestor, it can also mean that they animals just evolved similar forms because that's the best
structure for the job. When this happens it's
called convergent evolution. For example, a tuna, a penguin and a seal are all animals that spend all or a lot of their time in the water. One's a fish, ones's a
bird, and one's a mammal, but all three of them have
a suite of similar features, the most notable being a
really sleek fusiform body that can move through the
water like nobody's business and fins for propelling those bodies. But of course those three animals have very different evolutionary origins. Each of these three marine animals have independently converged on similar body shapes because they live in the same environment and need to do the same sorts of things. So instances of convergent evolution can make linking physical
structure of an animal to its evolutionary history
a little bit tricky, which is why for a long
time nobody really put much stock into comparative anatomy as proof of evolution. That is, until Thomas
Henry Huxley came along. (lively ragtime piano music) Thomas Henry Huxley was the
father of comparative anatomy and the father of modern paleontology and he invented the word agnostic to describe his spiritual views and he was the first person to conclude that birds evolved from
small carnivorous dinosaurs. (sighs) I'm glad I'm
sitting down for this. Plus we have much respect
for his facial hair. Huxley was born in England in 1825 and though he started out as a doctor after serving as a ship's
surgeon on a voyage to Australia in his 20s, he took to studying marine invertebrates. During his voyage he
sent all of his papers back to England and when he got home he found that he had become a kind of famous marine
invertebrate expert and he was admitted
into the Royal Society. Huxley made friends
with some other hot shot natural scientists
including Charles Darwin and a few years later,
when Darwin outlined his theory of evolution and
on the Origin of Species, Huxley is reported to have said, "how extremely stupid to
not have thought of that." In fact he became such
a huge Darwin supporter that everybody started
calling him Darwin's bulldog because threatened to cut the fool who badmouthed evolution. This is a good one. Huxley said when he was talking about On the Origin of Species, "old ladies of both sexes consider it "a decidedly dangerous book." You just got Hux slapped. With this new tool of
the theory of evolution, and in part to help promote
the theory of evolution, Huxley connected paleontology
and biology together by looking for similarities in anatomy in the fossil record, where he found all kinds
of interesting stuff, like some really obvious similarities between prehistoric horse fossils and modern day horses as well as between dinosaurs and birds, though nobody really bought his insights into the resemblance
between birds and dinosaurs for another 100 years. And just in case you
were still on the fence as to whether intelligence is heritable, Thomas Henry Huxley is the grandfather of Brave New World writer Aldous Huxley and of Sir Andrew Huxley who won the Nobel Prize for
Physiology or Medicine in 1963. And because all animals come from the same evolutionary origin, in addition to sharing
some anatomical structures like Huxley studied, we're also built from the
same rudimentary blueprint. Our cells work pretty much the same not matter what sort of animal we are. So while animals have different strategies for moving around and acquiring food, once the food is gotten,
all animals break it down, turn it into useful energy and distribute nutrients
and eliminate waste in pretty similar ways,
unless you're a sponge. Each of those functions is performed by collections of cells
that group together in the body to form tissues. There are four primary types
of tissues in the human body: the epithelial tissue,
the connective tissue, muscle tissue, and nerve tissue. Epithelial tissue is formed by cells that bind very closely together. A layer of it covers every organ and lines the digestive tract to prevent crazy acids and poop and stuff from going where
it's not supposed to go. Epithelial tissue can also
produce a slippery fluid to let your organs slide over each other like the membrane that lines
the inside of your ribs so that your inflating lungs don't build up friction as they expand. Most types of connective tissue are made up of fibrous
strands of collagen protein and it adds support and
structure to your body and holds your parts together. Some examples of connective tissue include the inner layers of your skin, your tendons, ligaments,
cartilage, and bone. But oddly enough, connective tissue isn't defined
by it's ability to connect, but instead by the presence
of an extracellular matrix, meaning that part of the tissue
extends outside of the cell. And so somewhat confusingly, blood and fat are also considered connective tissues. Muscle tissue is made up mostly
two specialized proteins, actin and myosin, which
can slide past one another and allow for movement. It also includes a bunch of other proteins including that longest word
in the world one, titan. And finally there's nerve tissue, which generates and conducts
electrical signals in the body. These electrical messages are managed by the nerve tissue in the brain and transmitted down the spinal cord to the rest of the body. Nerve tissue is made up
of two types of cells, the neurons which do the electrical work and the glial cells which
insulate and support the neurons. These tissues are then
organized into organs which perform different
functions in the body and these organs work
together in organ systems. For instance, most animals
have a digestive system made up of like a mouth and an esophagus and a stomach and intestines and an anus. And a lotta animals have a skeletal system made up of bones and tendons
and ligaments and cartilage. We're gonna be talkin'
about each of these systems in a lot more detail in a few weeks. These organ systems,
like many different kinds of anatomical structures are shared by lots of
different kinds of organisms, unless you're a sponge. Because about 1.6 billion years ago, an organism developed that
had a digestive system and a muscular system and suddenly that organism
was in it to win it. That organism was the common ancestor for all animals today and it's the reason why Shoshana and I are gonna hang out at the
animal family reunion.