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Video transcript

you and me we got some stuff in common more in common than say you and my dogs lemon and a B here for starters you and I are probably like the same species and lemon and a B or dogs which is a different species I think we have guessed by now this video is going to be about species but at the very end we're going to talk about dogs so hang in there cuz the puppies are coming but before we bust out the puppies let's talk about people our species Homo sapiens is the single remaining member of the genus Homo our buddies Homo erectus and Homo habilis and homo Neanderthal us but the farm a long time ago so these days all us Homo sapiens are pretty different from even our closest living relatives in the animal kingdom the chimps and bonobos humans are a species a specific type of organism that's different from all the other types of organisms out there but what is it that makes us human well we're a specific type of animal called a primate monkeys apes lemurs and tarsiers are also primates unless you're Sasha Baron Cohen or something most of us are lacking significant body hair we're bipedal meaning we stand on two feet and we've got these huge enormous brains that allow us to do all kinds of stuff like talk real good and solve complicated problems and write bad poetry during adolescence and you know also like figure out how little we can get away with tipping a mediocre waiter at a restaurant without seeming like a total prick that my friends is something that giraffes rarely have to deal with but being a species is more than just having a bunch of stuff in common instead we describe a species as a group of organisms that can interbreed and produce fertile offspring seems pretty simple right two of the same species that can produce blood Hey pay attention that last part is important the two organisms need to be able to produce fertile offspring it seems like it would be enough for organisms of the same species to be able to make babies but those babies need to be able to make babies too now it turns out to animals of different species can sometimes technically have a baby take for instance the noble liger Napoleon Dynamite's favorite animal which I would know because I had the very best Napoleon Dynamite costume in the United States for Halloween in 2005 but I didn't just bring up layers to brag a liger is what happens when a male lion and a female tiger have a little cub only it's not very little because a liger is generally larger than both of its parents and laggers are sterile which leads us to our understanding of what makes a species lions and tigers are different species because they don't produce fertile offspring together we call animals like loggers hybrids offspring resulting from the crossbreeding of two distinct species and even though hybridization between two animals is a dead end when it comes to creating a new species we know that through evolution or the change in heritable characteristics of a species across generations new species have formed in the past and they continue to develop all the time it's not the nail down every single way that this process that we call speciation can happen but we know the least a couple ways that species evolved into other species and they both involve one requirement reproductive isolation meaning that two populations of the same species can no longer make together successful note that I said successfully one-way populations can become isolated from each other is that they can mate but their offspring aren't fertile or viable ligers are a good example of this so are mules they're the product of a male donkey and a female horse and unlike lions and tigers donkeys and horses don't even have the same number of chromosomes so even though the donkey sperm can fertilize the horse egg the mule won't have the genetic instructions it needs to produce its own sex cells this kind of isolation is called postzygotic isolation because the parents can form a zygote together but after that it's all over for their lineage other examples of postzygotic isolation include pairings of species that always lead to miscarriage or no development of the embryo at all or things that produce like big fetuses that kill the mother at birth the other type of isolation is prezygotic meaning that the isolation happened between groups of the same species before an egg even thought about getting fertilized this could include stuff like behavioral changes within a species like when birds of the same species start singing to different songs to attract mates or when one group of a species that does all of its business in the daytime gradually becomes nocturnal so that the two groups never end up hanging out at the same time prezygotic isolation can also be geographic meaning simply that populations are separated by great distances or physical barriers so that they can no longer get together and bump uglies when one species diverges into two different species because of geographic isolation it's called allopatric speciation allopatric coming from the greek for different countries the two populations of the species end up evolving differently because the conditions are different on each side of this river here for instance it might be colder on one side of the river so the animals on this side grow thicker and more luxurious coats because those guys just do better over there they probably also put on thicker layers of fat and change their behavior and accumulate a bunch of other possibly random changes meanwhile on the warm side of the river these animals also accumulate changes and lose some fur add a bunch of sweat glands give it enough time and given a complete lack of gene flow between the two populations thick coated animals will eventually only be able to breed with other thick coated animals and sweaty animals with sweaty animals this propagation of specific traits based on how kick-ass those traits make the animal that has them is called natural selection and a guy named Charles Darwin or Chuck Darwin er Chuck Edie to his friends was the one who let us know what was up with natural selection and how it can lead to allopatric speciation now stop me if you've heard this one before but Darwin visited the Galapagos Islands in the 1830s so Darwin was obsessed with barnacles but that did not keep him from noticing the finches which were actually misidentified by him as gross Peaks on each Island which were all pretty similar to the finches on other islands and very similar to the ones in the mainland of South America but they were also obviously their own species if Darwin believed that the process that led to these finches becoming separate species was so slow that we couldn't actually witness the process we just had to take his word for it now for a long time after Darwin made these observations allopatric speciation was the main explanation for how species diverged but today we know that that's not the whole truth now we've got lots of new fangled DNA testing and other special gadgetry that tells us that one species can diverge into two without being geographically separated but instead when there reproductively isolated in some other way this is called sympatric speciation meaning same country speciation and it also means that it's time for a trip to the chair so here's a little biological love story for all you romantic sout there Peter and Rosemary grant to British evolutionary biologist they are in fact a married couple have since the early 1970s been spending six months of each year together on a secluded Island the Galapagos studying Darwin's finches trying to catch them in the act of evolving these are mind you the same animals that Darwin studied and the ones that he said were evolving at an imperceptibly slow pace the island in the Galapagos that the grants hang out on is called Daphne major and when they started their research in 1973 was occupied by two different Finch species the medium ground Finch and the cactus Finch but in 1981 another Finch arrived on Daphne major from a nearby island it was a ground Finch cactus Finch hybrid and it was a whole lot bigger than either of the local finches it's beak was also extra wide and it's song was like a mashup of the jams ground finches sang on its home island and the one sung on Daphne major so the newcomer set to work crooning to the local ground Finch ladies and eventually landed one the grants followed the descendants of these two birds for the next 28 years but after about four generations Daphne major experienced a severe drought which killed many of the finches there were only two surviving descendants of that one immigrant finch sort of like cousins of each other basically and they made it with each other and that seems to have set the stage for speciation to occur the descendants of these two survivors sang a very distinctive song that was learned from their parents which was different from the other Daphne major finches gradually as the finch population on the island rebounded the hybrid finches the great great great great grand chicks of that one bird began mating exclusively with each other in December of 2009 the grants announced that since the drought the lineage of that one immigrant ground Finch has been genetically isolated from the other local finches on the island so that my friends is both super romantic and also an excellent example of super quick sympatric speciation in action okay so I promised you puppies I'm gonna give you puppies you probably noticed that you know a Corgi looks pretty different from a greyhound they were bred to be different scourges were bred to hurt animals in guard mouses while greyhounds were bred know mostly to run dog breeding kind of takes the natural out of selection in fact it's what we call artificial selection but it's still a kind of selection so you've probably wondered what it would be like if a Corgi and a greyhound had puppies together because they can have puppies together even though that's really weird where's that lemon you're both girls oh well you know anyway my point here is that they're the same species meaning that these dogs even like different dogs like an Irish Wolfhound and in Chihuahua could have fertile offspring together like how how how would how various dog breeds are similar enough that postzygotic isolation isn't an issue but in a natural setting a chihuahua wolf hound pairing would be extremely rare because of the you know the difficulties involved in the getting it on process or prezygotic obstacles they think about it like this if you were to put a bunch of Chihuahuas and a bunch of wolf hounds on an island somewhere it probably wouldn't breed together and if they did the birthing process at least for the Chihuahua mommies would be ah Oh God but what this means is that the gene flow between the two groups would stop and they would become reproductively isolated over time they would become different enough that they could no longer successfully breed together at all and thus become different species
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