What is a Species? Crash Course Zoology #13 - Free Educational videos for Students in K-12

What is a Species? Crash Course Zoology #13 - By CrashCourse

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00:0-1	you know what sounds good right now , a taxonomic
00:03	sandwich . Taxonomic sandwiches usually show us how much time
00:07	has passed since two animals with the same abbreviated latin
00:11	name split off from their common ancestor . But we
00:15	can also make taxonomic sandwiches between any two animals .
00:19	It's just like using two different types of breath ,
00:22	like together horses , Donkeys and zebras formed the genus
00:26	Equus . If we make a taxonomic sandwich between a
00:30	Equus quagga , the plains zebra and Equus ferus .
00:33	Karbala's the domestic horse . There's 7.7 million years of
00:39	filling . But the Donkey Zebra Sandwich only has 2.8
00:44	million years of filling because donkeys are more closely related
00:47	to zebras than horses . So basically zebras are flashy
00:52	donkeys and not striped horses . And yet despite being
00:56	separated by millions of years of evolution , these three
01:00	species sometimes mix and match their mates , producing hen
01:04	ease sources , donkeys and yes , mules and if
01:08	they look alike and can reproduce together , it kind
01:11	of seems that they may not actually be different species
01:15	. Scientists put animals into several categories each more specific
01:19	than the last describing an animal's features and who its
01:23	closest evolutionary relatives are . But the bedrock of that
01:27	classification system , the taxonomic rank of species isn't nearly
01:32	as solid as a foundation as we'd expect . I'm
01:35	Ray Wynne Grant and this is crash course sociology .
01:40	Yeah . Yeah . Mhm . Back in episode one
01:49	, we define a species as a group of all
01:52	the animals of the same type that can breed together
01:55	over multiple generations , which is a perfectly valid way
01:59	to define a species . But there are over two
02:02	dozen other distinct ways of defining a species . Now
02:06	that we've seen the amazing diversity of animals , we
02:09	can return to the species problem , which is a
02:12	set of questions like what happens if two different types
02:15	of animals have babies that arise whenever we try to
02:19	define what a species actually is ? There's even a
02:22	whole sub field called micro taxonomy dedicated to organizing the
02:27	millions of animals out there into human made boxes and
02:31	trying to resolve all the exceptions that come up ,
02:34	which is not just important to the zoologists , but
02:37	the animals themselves , to What species and animals classified
02:42	as matters for things like the US . endangered species
02:45	act and comparable laws worldwide that provide legal protection for
02:49	certain organisms on the basis of their species . A
02:53	common method for drawing lines between species in the 19th
02:56	century was to rely on observations . The morphological species
03:01	concept says that members of the same species look the
03:05	same as each other but different from members of another
03:08	species . But some species vary so much and how
03:11	they look , that they overlap with other species in
03:14	size , shape , color or whatever , making it
03:17	hard to know where to draw the line . The
03:20	opposite problem occurs to some distinct species look so similar
03:25	that it's almost impossible to tell them apart based on
03:28	physical characteristics . Fortunately , we have more methods ,
03:32	like the biological species concept , which says that a
03:36	species is a group of naturally or potentially interbreeding populations
03:40	that are reproductively isolated from other groups , which means
03:45	we have a group of animals that can combine their
03:47	genetic material using sexual reproduction to make more animals .
03:52	And if any animals in the group tried to mate
03:55	with animals outside the group , they can't produce fertile
03:58	offspring either because their offspring , which is called a
04:02	hybrid because it's the offspring of two different types of
04:04	animals never develops because their DNA just can't work together
04:09	or because the hybrid is almost always sterile , like
04:13	a mule . But the biological species concept is also
04:17	too narrow of a definition . It doesn't work for
04:20	the many a sexually reproducing organisms like aphids who clone
04:25	themselves instead of mixing their DNA with another individual or
04:30	different species whose hybrid offspring can reproduce like female ,
04:34	like ear's . And the caveat of potentially interbreeding has
04:39	always been confusing potentially as in it could happen in
04:43	the wild , or potentially as in it could happen
04:46	in a zoo . Another option is to use the
04:49	cohesion species concept , which was introduced in the late
04:53	1980s and was written to address some of these drawbacks
04:57	. The cohesion species concept defines a species as a
05:01	population or series of populations with genetic or demographic cohesion
05:07	, meaning they all have pretty similar genes and traits
05:11	. This allows for a sexually reproducing animals and hybrids
05:15	to exist as long as they aren't so common that
05:19	they change the characteristics of the population as a whole
05:22	. Or we could use the filo genetic species concept
05:25	, which was developed around the same time and defines
05:29	a species as a group with a shared and unique
05:31	evolutionary history . Instead of focusing on living animals swapping
05:36	and sharing genes , all members of the species are
05:39	descended from the same common ancestor and share a combination
05:43	of defining traits that they all got from that ancestor
05:47	. The tricky part is that using the file a
05:49	genetic species concept , it's possible to define a near
05:53	infinite number of species because most populations will have many
05:58	sub populations that are very slightly different from others .
06:02	So we have to decide where to draw the line
06:05	. Like the black bears that live in the Everglades
06:07	could be different from those on the tundra or in
06:10	the Rocky Mountains . Both the cohesion species concept and
06:14	the filo genetic species concept work by comparing the DNA
06:18	of one animal to another with different techniques to decide
06:22	if they're related enough to belong to the same species
06:26	. DNA barcoding focuses on a few specific genes are
06:30	part of the DNA that are suspected to vary a
06:32	lot between species , but not too much between individuals
06:37	. The barcode , whereas genetic similarity takes into account
06:41	the whole genome or entire DNA sequence , but there's
06:46	no one right way to define a species . And
06:49	even still , zoologists will often combine multiple definitions and
06:54	tools in their work . It's hard work defining a
06:57	new species . Let's go to the thought while hiking
07:01	in the mountains just outside santa , barbara California .
07:04	We come across this thing we've never seen before .
07:08	We take observations about its behavior and where we found
07:12	it and photos of its morphology or how it looks
07:15	. We'll also want to get something with its DNA
07:18	in it and ideally bring a specimen or two back
07:21	to the lab because it's easy to miss things in
07:24	the field and allows other researchers to check our work
07:27	once back , the first thing we do is check
07:30	there are no previous records of an animal matching this
07:33	description based on our notes . Now we write up
07:36	our manuscript with our field observations and using the specimens
07:39	we brought back with us . We need to explain
07:42	how our species differs from other described species and how
07:47	it fits in the meadows . Oh , and Family
07:49	tree . One part a lot of zoologists focus on
07:52	is its sex organs because they tend to be very
07:55	specific to a single species , whereas other differences could
07:59	be due to something like diet or age . And
08:02	if we think it's a new species based on our
08:04	definitions , we also get to name it . This
08:07	creature looks like others in the family Ursa Day .
08:11	It doesn't have a false thumb , like a panda
08:14	or a spectacle bear . So it's probably related to
08:17	black bears and Grizzlies in the genus ercis . So
08:20	let's call it ursus stuff Phyllis . Now we submit
08:24	our manuscript to an academic journal and if it's accepted
08:28	, will have successfully described a new species . Thanks
08:32	thought bubble . About 11,000 new animal species are described
08:37	each year by zoologists , but knowing when to investigate
08:42	a possibly new species is an art in itself .
08:45	Sometimes animals just live in a place where we haven't
08:49	seen similar species before . Or sometimes they look like
08:52	other species but are separated by a geographic feature that
08:56	could stop them from interbreeding . Ultimately categorizing animals into
09:01	different species helps us humans wrap our heads around the
09:05	stunning level of diversity around us . But even if
09:08	we can agree on one definition of a species ,
09:12	there are a lot of cases where species aren't nearly
09:15	as separate as we might think . It comes down
09:18	to gene flow or the transfer of genetic material from
09:21	one population to another or like from parents to offspring
09:26	. But there are also situations where animals be considered
09:29	to be separate . Species can share genes like hybrids
09:34	probably won't just mate with hybrids . They usually end
09:38	up mating with one of their parents , species creating
09:41	offspring that has genes from mostly , but not entirely
09:45	one species like paradise fighters in the genus Heyburn Atis
09:50	. In some species , males have brightly colored ornaments
09:54	that they show off in their courtship dances . But
09:57	paradise spiders are notorious for hybridizing . The males will
10:01	dance for pretty much any species of female . These
10:05	offspring continue mating and before you know it , genes
10:09	from one species have made it into the gene pool
10:11	of another and those genes can stick around which is
10:15	a process called intra aggression . And integration can make
10:19	things confusing . Like take the big bushy eyebrows of
10:23	these three paradise fighters . Thanks to all the hybridization
10:27	between these different spiders , these eyebrows might have evolved
10:31	in one species and then spread to others . But
10:35	all that integration also makes it hard to be sure
10:38	. And even harder to know who had the browse
10:40	originally . Only one thing is clear . There is
10:44	a lot of DNA moving back and forth between these
10:47	separate species . Those sometimes we can see some organization
10:52	in the gene flow chaos if we're dealing with ring
10:55	species or a series of neighboring populations that can interbreed
10:59	with the groups close to them , but not other
11:01	populations that are further away until we get to ends
11:05	to our ring . Like the species of larry's goals
11:08	in the arctic , the european herring goal can mate
11:11	with the american herring goal and the american herring goal
11:14	can mate with the East Siberian goal and so on
11:18	as we circle or ring around the North Pole .
11:22	The last species in the ring is the lesser black
11:25	backed gull of northwestern europe , which can't meet with
11:29	the first species in the ring . The european herring
11:32	goal because there to genetically different , there are other
11:35	ring species out there , even if their locations don't
11:38	quite perfectly formed rings like western fence lizards might be
11:42	a ring species . So we started this episode by
11:46	asking what is a species . And while some definitions
11:50	of species are more robust are commonly used than others
11:54	, none of them perfectly fit the true diversity of
11:57	all animals into human defined categories . The species problem
12:03	is one of the many enduring mysteries in zoology and
12:07	in our next and final episode will dive into the
12:10	true frontiers of the field and even more open questions
12:15	if you want to learn more about the western fence
12:17	lizard , bizarre beasts just did a video on them
12:21	. In this series , hosts hank green and Sarasota
12:24	introduce you to a new bizarre beast and explore what
12:27	makes these animals so weird to us from birds whose
12:31	babies have claws on their wings to lizards with glowing
12:34	bones , the show examines the how and why of
12:38	some of the world's most amazingly strange critters and if
12:42	you want to take a bizarre beast home , check
12:44	out the bizarre beasts pin club . The links for
12:47	the channel and the pin club are in the description
12:49	below . Thanks for watching this episode of crash course
12:53	ideology , which was produced by complexity in partnership with
12:56	PBS and Nature . It's shot on the team Sandoval
12:59	Pierre stage and made with the help of all these
13:01	nice people . If you'd like to help keep Crash
13:04	Course free for everyone forever , you can join our
13:06	community on Patreon .

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