When Two Species Mix
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When Two Species Mix


{♫Intro♫} Organizing living things into kingdoms and families and species and stuff helps us understand
the vastness of life on Earth. It gives it order. And we tend to think of these categories as
fixed, with a species being a species no matter what. Except… life doesn’t have to follow our
rules. Species interbreed to produce hybrids more
often than we tend to think. And understanding how and why they break the
rules can help us understand them even better. One of biologists’ most commonly used methods
for differentiating one species from another is called the biological species concept. It defines a species as a population of organisms
that regularly interbreed and produce fertile offspring. So by that definition, if two different species
breed, they can’t have fertile offspring. Which checks out if you think about hybrids
intentionally created by humans — like mules or ligers. They’re almost always sterile and can’t
produce offspring. But what about when humans aren’t monkeying
around with other species’ gene pools? Actually, interbreeding happens a lot. Scientists used to think hybridization was
a genetic dead end. But we now understand that it’s a major
driving force for speciation, or the creation of new species. We can see evidence for it happening all over
the place, especially in plants. In fact, according to one study published
in 2005, natural hybridization occurs in 25 percent of plant species and about 10 percent
of animal species alive today. And this seems to be because plants are more
likely than animals to be polyploid — meaning they can have extra sets of chromosomes. This can happen if the parent species accidentally
duplicates its DNA, producing a complete extra set of chromosomes. Long story short, this is terrible news for
being able to reproduce, because cells tend to freak out if the number of chromosomes
doesn’t match up. These polyploid individuals can now only mate
with other polyploids — barring a genetic trick here or there. Now, it’s reproductively isolated from its
parent species, but can mate with similar individuals. Meaning — it’s a new species! And this process is why we have pizza dough,
cookies, and parker house rolls — that is, wheat. Most wheat is actually a polyploid hybrid. The group of wheat known as Triticum naturally
has multiple sets of chromosomes — which makes it easier for them to hybridize. So when humans started to domesticate various
wild wheats to make them better for harvesting, the domestic and wild strains were still able
to interbreed. The gene flow from wild and domestic strains
of wheat over time lead to the creation of new hybrid wheat species, like durum wheat,
which is used to make pasta. But animals are much less tolerant of polyploidy
than plants – it’s usually fatal in animals because our cells don’t handle the extra
DNA so well. So with animals, we more often see homoploid
hybrid speciation, where there’s no change in chromosome number. And while scientists aren’t always 100%
sure how homoploid hybrid speciation works, some think it has to do with the mixing of
genes. One way to achieve this gene mixing is through
backcrossing. Backcrossing is when two species mate and
produce a hybrid, then that hybrid mates with one of the parent species and manages to produce
fertile offspring. When this happens repeatedly over generations,
it’s called introgression. Genes transfer back and forth like two different
decks of cards being shuffled and dealt for a poker game. Sometimes you get more cards from one deck
than the other, so the hybrid might look more like one parent than the other. And much like in a card game, you can be dealt
a losing hand — where the hybrid dies out and the two distinct species remain. Or you can get a winning combination, where
the hybrid inherits a lucky combination of genes that make it fitter than either of its
parents. Over time, the hybrid’s combo of genes wins
out and a new species forms. Such is the case with the hybrid Italian sparrow. When researchers looked at its genes in a
2018 study, they found that some individuals had more genes in common with one parent species,
house sparrows — while others got more genes from their other parent, the Spanish sparrow. In fact, different combinations of genes seemed
to be more successful in different environments. Even Darwin’s famous finches — the birds
he used to demonstrate incremental adaptations to different environments — seem to be able
to hybridize with each other. And that genetic mixing may help drive their
ability to rapidly adapt to changing conditions on the Galapagos islands they call home. So try as we might to create order in the
universe by carefully categorizing and defining things, nature doesn’t care about our definitions! And while the biological species concept can
be useful, evolution is a bit of a rebel. And hybrids are material for evolution to
work with. Thanks for watching this episode of SciShow,
which was brought to you with the help of our patrons. Patrons get access to cool perks, including
our very own patron Discord server, and they make it possible for us to bring free educational
videos to everyone. So thanks! If you want to join, head over to patreon.com/scishow. {♫Outro♫}

100 thoughts on “When Two Species Mix

  1. How are these videos free when I can still get advertisements on them? What’s the point of supporting patrion when this channel gets ad revenue already?

  2. Some of the separately created species are genetically similar enough with each other that they can interbreed and produce offspring. Usually the offspring are sterile.

  3. Back where I used to live I'd see the mallard ducks and I'd see Mascovy ducks. And once in a while you'd see a freakshow of a duck with a pimply face like a Mascovy and also a green feathered head like a mallard.

  4. And yet scientists totally deny the definition of species when it comes to humans, insisting Neanderthal was a separate species even though they interbred readily.

  5. “so try as we might to create order in the universe by carefully categorizing and defining things, nature doesn’t care about our definitions”

  6. I heard they have various health problems and a shorter life span. It is not really a good thing biologists should stop messing around and make proper research on those unlucky fellows.

  7. Wait did you just explain away Darwin’s origin of the species with a much simpler, easier testable explanation for the Finches using hybridization?

    lol. Science, not the rock of truth that society makes it out to be. More like the water of observation.

  8. Excellent video! One note: either Michael's face makeup isn't matched perfectly or there's something funny going on with the lighting

  9. Was this vid inspired by the comment thread on classifying Homosapiens and Neaderthals as separate species on a vid Hank Hosted recently?

  10. I love that you're wearing a Kurzgesagt shirt. SciShow and Kurzgesagt are my two favorite learning channels and I would eat my socks to see a collaboration!

  11. Hate to say this, but this is a huge part of racism. Some human populations have been seperate for long enough to become very different. The point being that racism is normal because we were on the way of becoming a seperate species, had we not invented means for long distance travel. Its sad but it is what it is. Luckily our human brains can stand above this. However often instinctual stuff like look and smell and behavior messes with that ability. I think this is a problem that is overlooked. A human is NOT a human. We should have equal rights in society, but we should not want to be equal and accept the fact that we are different

  12. I mean this shouldn’t surprise people given that humans and Neanderthals along with various other hominids interbred for thousands of year.

  13. This could actually explain why we humans have genes from other human species over the eons, such as human-Neanderthal crosses. This answers so many of my questions.

  14. Does this mean that if given time, Down's syndrome people that interbreed would eventually give rise to a new species?

  15. One thing you didn't explore. How about human hybridization, if such a thing exists. I do know that some people have neanderthal DNA

  16. Everyone dog lion etc etc cross breeding and here i m still waiting for one kiss man i m so single and will die single

  17. Female hybrids are usually still able to re produce regularly with both the species they cane from, it’s just makes that are usually infertile

  18. Just what if one day human breaks the boundaries and mix the human genes with animals. There are exploration films like Splice, or those villains like Cheetah/Man-Bat from DC or Man-Spider from Marvel. It would brought to question what defines as humanity.

  19. By naming things humans think (or tell themselves) they understand it. In actuality naming things impedes understanding.

  20. OMGAWD, isn't this genetic manipulation??? Only, worse still, instead of deliberate, well thought out manipulation, this is just random chance. Where are the bioethicists???

  21. Talking about it like a Deck of cards makes it sound like evolution is some kind of really advanced video game, not that it's a bad thing.

  22. Many of our beautiful tropical fish such as red wag platies and red wag swordtails come from the combinations of two species of fish.

    Their are no red platies or swordtails in the wild. Neither do any wild fish have the wag feature (black fins). In captivity the first generation of a cross between swordtails and plates is a read fish that looks like a short bodied red swordtail. Perhaps they will have the way feature. To get a red platy these fish are bred with platies and the best red babies are kept. This is repeated to get a bright red fish with the body shape of a platy.
    To get red swordtails the hybrids are bread with swordtails saving the nicest babies to get a red fish that seems for all the world to be a swordtail.

    However all of these fish are mixed between two species.

    In the wild more drab coloring favors survival. Perhaps some ancient fish had these characteristics. Some babies didn't and they survived better while the more brilliant fish were eaten. Only drab fish remained.

    We humans got a hold of them and started breading for color.

  23. Oh my God he caught the Trump sickness look at him he's turning orange like an Oompa Loompa too

  24. When you say hybrid, how closely related do the 2 species need to be? Are we talking 2 different variations of sparrow very closely related in ancestry?

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