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

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



Transcript
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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