Brainy & Brainless Animals: Crash Course Zoology #5 - Free Educational videos for Students in K-12

Brainy & Brainless Animals: Crash Course Zoology #5 - By CrashCourse

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00:0-1	There are lots of big questions out there that we
00:02	just don't know the answer to like how we store
00:05	and retrieve memories or why we sleep and dream .
00:09	But alongside these complex issues , there are some deceptively
00:13	simple questions . Thousands of years of science and observation
00:17	haven't been able to answer yet . Like what is
00:20	a brain ? We humans love to focus on our
00:24	brain power and our ability to use complex tools and
00:27	languages solve problems and grapple with deep philosophical questions .
00:32	But those might not be important tasks for other animals
00:36	. And we might think of big brained animals like
00:39	primates and dolphins as being the smart ones . But
00:42	you don't need a big brain to do a lot
00:45	of smart things like recognize your family or trick your
00:49	prey and we'll even see how some animals literally lost
00:53	their minds , opting for a simpler but no less
00:57	evolved lifestyle . I'm Ray Wynne Grant and this is
01:00	crash course sociology . Mhm . Brains look different across
01:13	the vast wildness of meadows Owa . But for the
01:16	most part , animals have some sort of nervous system
01:19	which coordinates the actions of the other systems in the
01:22	body . And we can think of a brain as
01:24	the mission control center of the nervous system . Brains
01:28	are organs or groups of tissues or cells that all
01:31	do the same thing that are made up of big
01:34	bunches of nerve cells called neurons . Neurons send and
01:39	receive information from other cells using electrical signals and process
01:44	that information in order to respond in some way like
01:48	to move . And they have two main parts that
01:51	help them with all that information . Cell bodies and
01:55	tails called axons . Groups of neuron cell bodies that
01:59	work together as a unit are called ganglia and bunches
02:03	and bunches of interconnected ganglia . Plus a few other
02:06	things to hold everything together are what make up brains
02:10	. The nerve cells in ganglia send instructions from the
02:13	brain to other cells like to tell muscles to contract
02:18	. Though how a bunch of Ganglia becomes a cooperative
02:22	network of millions of cells is still a mystery .
02:25	On the other end , a bunch of neuron axons
02:29	is called a nerve and nerves can reach throughout the
02:32	body in order to send information to the brain when
02:36	they sense things like pain , light or sound .
02:39	And for the vast majority of animals we know about
02:41	in 2021 brains or at least some kind of nervous
02:46	system are pretty fundamental to two key animal traits .
02:50	Multicellular charity and movement . A nervous system keeps the
02:55	sometimes millions and millions of cells in touch and coordinates
03:00	their actions to digest food or wag a tail just
03:04	like a skeleton . Nervous systems are part of the
03:06	scaffolding that builds an animal body . But since brains
03:10	are squishy , it's hard to get a lot of
03:14	information about how they developed from fossils , squishy stuff
03:19	usually gets broken down long before fossils form . So
03:22	instead we can examine early diverging plaids , which are
03:26	groups of animals that last shared a common ancestor with
03:29	other animals a very long time ago as a window
03:32	into what early nervous systems might have looked like .
03:35	The simplest , but also the most mysterious nervous system
03:39	belongs to file um peripheral to the sponges . Sponges
03:43	don't have neurons yet somehow they can still coordinate their
03:47	cells to squeeze water through their bodies or close up
03:50	to shield themselves from predators . Instead , we think
03:53	peripheral cells can send electrical and chemical signals to each
03:57	other . Somehow we're still working on how then between
04:02	whatever . Not really a nervous system . Sponges have
04:04	going on and animals with heads full of brains more
04:08	like ours . We have animals like 10 offers and
04:11	Nigerians , the file A . Of comb jellies and
04:14	jellyfish , respectively . Like sponges , neither comb jellies
04:18	nor jellyfish have a brainy mission control in their head
04:22	, but they do have a diffuse network of ganglia
04:25	and nerves spread throughout their body called a neural net
04:29	. While a neural net seems like the next evolutionary
04:33	step up from nerveless sponges . Remember we're still trying
04:37	to figure out the animal family tree , so if
04:40	once and only once upon a time , the last
04:45	common ancestor of all medicines evolved a nervous system that
04:49	would mean all animals inherited the same basic nervous system
04:53	. So studying 10 offers could help us understand early
04:57	stages of nervous system evolution . For example , It
05:00	would mean that ancient sponges probably had a more complex
05:04	nervous system like 10 offers in the past , but
05:07	lost it at some point . Or maybe nervous systems
05:11	evolved twice once in a lineage containing Nigerians and military
05:16	ins And once in 10 offers , which is a
05:19	compelling theory because the 10-4 nervous system is just so
05:23	strange . Like they don't have the genes or the
05:26	proteins to make most of the neuro transmitters , The
05:29	chemical signals that neurons send to each other that all
05:33	other animals use like dopamine and serotonin . And if
05:37	10 offers came up with a nervous system all on
05:39	their own , it leads to some interesting questions about
05:43	who were the first animals to diverge from the rest
05:46	, which until recently we were pretty sure were the
05:49	sponges . So finding an answer could reshape the entire
05:53	animal family tree . We do know that central brains
05:58	bundles of ganglia stuffed into ahead show up on the
06:02	Villa terrian branch of the tree , which are all
06:04	the animals with mirror image symmetry . All but four
06:08	of the 35 Fila are on this branch . So
06:12	there's a huge variety of military in brains , like
06:16	arthropods , Arbilla Terrians that pack a lot of brainpower
06:20	into a tiny space . For example , insects have
06:24	a brain in their head , pack more ganglia under
06:27	and behind their esophagus And have a few more distributed
06:30	throughout their body . Other billet , Terrians , like
06:33	core dates and cephalopods tend to be much larger and
06:37	can have much larger brains . At least 80% of
06:40	brain size is determined by an animal's body size ,
06:44	but that last 20% that comes from things like sex
06:48	, age and genetics can tip the scales unexpectedly .
06:52	So to compare brains , zoologists can use something called
06:56	the encephalitis station quotient or EQ , which is how
07:00	much bigger or smaller in animals . Brain is compared
07:04	to what we expect for its body size . An
07:06	animal with a brain that's the expected size has an
07:09	eQ of one . A mouse has an eQ of
07:13	0.5 , meaning that its brain is only half the
07:16	size of what we predict . Dolphins have brains about
07:19	four times as big as we'd expect . So their
07:22	eQ is four . Of course . We devised the
07:25	system and we calculated a species predicted brain size using
07:30	just data from fellow mammals . So maybe it's not
07:33	surprising it makes us look good . Humans have over
07:37	seven times more brains than we predict , given our
07:41	body size . But other fila , which have brains
07:44	that might be wired in fundamentally different ways , could
07:47	be playing by different brain to body size rules like
07:51	octopuses have a large central brain , but two thirds
07:55	of the neurons are in their super smart arms .
07:58	Intelligence , which to us humans means being able to
08:02	acquire knowledge and skills to do something with them is
08:05	tricky to talk about and even trickier to measure ,
08:09	especially in non human animals . Often when we hear
08:12	about non human animals being smart , it's because they
08:16	can do things that humans do like paint or open
08:19	a jar or solve a puzzle . But lots of
08:22	other non human animals are smart in their own way
08:25	and have ample brainpower to do all the things they
08:28	need to do to survive and thrive . So if
08:31	we had to animals say like an elephant and a
08:34	honeybee who's smarter , let's go to the thought bubble
08:39	. Instead of focusing on human like tasks , we
08:42	could test something that both humans and most non human
08:45	animals would agree is important . Being able to tell
08:49	close relatives from strangers and adjust your behavior . Under
08:53	this criteria , a lot of animals passed the test
08:57	. Both elephants and honeybees can tell some individuals from
09:00	others which is helpful for managing a hive or a
09:04	herd . So this round is a draw . In
09:06	the second round we could compare brain size . Obviously
09:11	a honeybees brain is literally a lot smaller than an
09:14	elephants , but a honeybees brain is about 4% of
09:17	their total body mass , whereas an elephants is only
09:20	about 0.18% . Brain size can be tricky though because
09:25	it includes neurons but also other stuff like water .
09:28	So in round three we can compare the smarts of
09:32	elephants and honeybees by testing their neurological processing power ,
09:36	Which is basically counting how many neurons they have more
09:40	neurons means more processing power or potential for intelligence .
09:44	A honeybee has 960,000 neurons while our elephant has 257
09:51	billion neurons . So the elephant easily takes this round
09:55	. Generally counting neurons works pretty well Until we realize
09:59	bigger brains usually also naturally have more neurons in our
10:04	fourth and final round , we can refine our counts
10:08	and compare the number of neurons and animal has relative
10:11	to how big it is when we do that .
10:14	Honey bees have 200 times as many brain cells relative
10:18	to body size as our elephant with billions of neurons
10:22	. So who's really the smart one ? Both the
10:25	honeybee and the elephant can get around feed themselves and
10:29	manage a complicated social life . The elephant has a
10:32	bigger cognitive engine overall , but the bees engine is
10:35	much bigger for its body . Thanks thought bubble ,
10:39	measuring intelligence and animals is hard because we have to
10:43	grapple with the fact that intelligence means different things to
10:47	different animals and we have to design tests that match
10:50	some animal lineages even seem to have given brains a
10:54	try and then decided they weren't all that great ,
10:57	losing them over time . Like sea urchins , sea
11:00	stars and other akin to terms it kind of terms
11:03	of today's world have radial cemetery , which means they're
11:06	symmetric around a central point . But we know they
11:10	evolved from bilaterally symmetrical animals and most military ins have
11:15	heads which tend to get filled with some sort of
11:17	brain . So ancient aquino terms probably had brains ,
11:21	but modern ones have simple neural nets running from each
11:25	arm to their mouth in the center . A less
11:29	complex nervous system was all that ancestor needed for their
11:32	filter feeding lifestyle . And for animals that don't need
11:35	to do a lot of thinking or other complex tasks
11:38	. Having a big brain isn't only pointless . It
11:41	can be a liability . Brains are incredibly active organs
11:45	and need fuel to function . Our brains are only
11:48	about 2% of our body weight , but use about
11:51	20% of our energy . That's a lot of energy
11:55	to sink into an organ you might not need like
11:57	every other part of an animal , brains and nervous
12:00	systems evolve over time in response to the challenges in
12:03	an animal's environment and lifestyle . And sometimes it's much
12:07	smarter to have a tiny , simple brain than a
12:10	big complicated one . Next episode will look into one
12:14	of the senses that the brain uses to gather information
12:17	about an animal's environment . See you there , its
12:22	site , we're going to talk about site . Thanks
12:24	for watching this episode of Crash course ideology , which
12:27	was produced by complexity and partnership with PBS and Nature
12:30	. It's shot on the team Sandoval Pierre stage and
12:33	made with the help of all of these nice people
12:35	. If you'd like to help keep crash course free
12:37	for everyone forever , you can join our community on
12:40	Patreon .

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