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Organizing living things into kingdoms and families and species and stuff helps us understand the vastness of life on Earth.
将生物组织成王国、家庭、物种等有助于我们理解地球上生命的浩瀚。
It gives it order. And we tend to think of these categories as fixed, with a species being a species no matter what.
给了它们一种秩序。我们倾向于认为这些类别是固定的，无论如何，一个物种就是一个物种。
Except… life doesn't have to follow our rules. Species interbreed to produce hybrids more often than we tend to think.
除非，生命不遵循我们制定的规则。物种杂交的频率比我们想象的要高。
And understanding how and why they break the rules can help us understand them even better.
了解它们如何以及为什么违反规则可以帮助我们更好地理解它们。
One of biologists' most commonly used methods for differentiating one species from another is called the biological species concept.
生物学家们最常使用的区分物种的方法之一被称为生物种概念。
It defines a species as a population of organisms that regularly interbreed and produce fertile offspring.
它将物种定义为一群定期杂交并产生可育后代的生物。
So by that definition, if two different species breed, they can't have fertile offspring.
根据该定义，如果两个不同的物种繁育，它们无法生育后代。
Which checks out if you think about hybrids intentionally created by humans, like mules or ligers.
如果你认为有一些动物是人类故意创造的混血儿，比如骡子或狮虎，可以用这个来验证。
They're almost always sterile and can't produce offspring.
它们几乎都是无法生育。
But what about when humans aren't monkeying around with other species' gene pools?
但如果人类不去摆弄其他物种的基因库，情况又会怎样呢？
Actually, interbreeding happens a lot. Scientists used to think hybridization was a genetic dead end.
事实上，杂交经常发生。科学家以前认为杂交是一个基因的死胡同。
But we now understand that it's a major driving force for speciation, or the creation of new species.
但我们现在知道，它是物种形成或创造新物种的主要驱动力。
We can see evidence for it happening all over the place, especially in plants.
我们可以在任何地方看到它发生的证据，尤其是在植物中。
In fact, according to one study published in 2005,
事实上，根据2005年发表的一项研究，
natural hybridization occurs in 25 percent of plant species and about 10 percent of animal species alive today.
25%的植物物种存在自然杂交行为， 大约10%的现存动物物种存在自然杂家行为。
And this seems to be because plants are more likely than animals to be polyploid, meaning they can have extra sets of chromosomes.
这似乎是因为植物比动物更有可能是多倍体，这意味着它们可以有额外的染色体。
This can happen if the parent species accidentally duplicates its DNA, producing a complete extra set of chromosomes.
亲本种不小心复制了它的DNA，产生一套额外的完整染色体，就会发生这种情况。
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.
长话短说，这对生殖能力来说是个可怕的消息，因为如果染色体数目不匹配，细胞就会崩溃。
These polyploid individuals can now only mate with other polyploids, barring a genetic trick here or there.
这些多倍体个体现在只能与其他多倍体交配，除非这里或那里出现基因突变。
Now, it's reproductively isolated from its parent species, but can mate with similar individuals. Meaning, it's a new species!
现在它从它的亲本种中分离出来繁殖，但可以与相似的个体交配。这意味着一个新的物种！
And this process is why we have pizza dough, cookies, and parker house rolls, that is, wheat.
因为这个过程，我们拥有了匹萨面团、饼干和派克宾馆面包卷，也就是小麦。
Most wheat is actually a polyploid hybrid.
大部分小麦其实是多倍体杂交。
The group of wheat known as Triticum naturally has multiple sets of chromosomes which makes it easier for them to hybridize.
小麦属天生拥有多组染色体，因此它们更容易杂交。
So when humans started to domesticate various wild wheats to make them better for harvesting,
所以当人类开始驯化各种野生小麦以使它们更适于收割时，
the domestic and wild strains were still able to interbreed.
家系和野生品种仍然能够杂交。
The gene flow from wild and domestic strains of wheat over time lead to the creation of new hybrid wheat species,
随着时间的推移，来自野生和家养小麦品系的基因流导致了杂交小麦新品种的产生
like durum wheat, which is used to make pasta.
比如做通心粉的硬质小麦。
But animals are much less tolerant of polyploidy than plants –
但是动物对多倍体的耐受性远不如植物
it's usually fatal in animals because our cells don't handle the extra DNA so well.
这对动物而言通常是致命的，因为我们的细胞不能很好的处理额外的染色体。
So with animals, we more often see homoploid hybrid speciation, where there's no change in chromosome number.
所以在动物身上，我们更经常看到的是同倍体杂交物种形成，即染色体数目没有变化。
And while scientists aren't always 100% sure how homoploid hybrid speciation works, some think it has to do with the mixing of genes.
科学家也并不是百分百确定同倍体杂交物种形成是如何进行的，一些科学家认为这个基因混合有关。
One way to achieve this gene mixing is through backcrossing. Backcrossing is when two species mate and produce a hybrid,
实现基因混合的一种方法是通过回交育种。回交育种是指两个物种交配并产生杂交后代，
then that hybrid mates with one of the parent species and manages to produce fertile offspring.
然后这个杂交物种与一个亲本种交配，并设法产生可育的后代。
When this happens repeatedly over generations, it's called introgression.
当这种情况在几代中反复发生时，就被称为“基因入侵”。
Genes transfer back and forth like two different decks of cards being shuffled and dealt for a poker game.
基因来回转移，就像扑克牌游戏中两副不同的牌被洗牌和发牌一样。
Sometimes you get more cards from one deck than the other, so the hybrid might look more like one parent than the other.
有时你从一副牌中得到的牌比另一副多，所以其中一个杂交物种看起来更像亲本种。
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.
就像在纸牌游戏中，你可能会输掉一副牌，即杂交物种消失了，而两个非凡种仍然存在。
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.
或者你可以获得一个最佳组合，即这种杂交物种遗传了一组幸运的基因组合，使它比亲本种中的任何一个都更健康。
Over time, the hybrid's combo of genes wins out and a new species forms.
随着时间的推移，混合基因的组合胜出，一个新的物种形成。
Such is the case with the hybrid Italian sparrow. When researchers looked at its genes in a 2018 study,
杂交的意大利麻雀就是这样。当研究人员在2018年的一项研究中研究它们的基因时，
they found that some individuals had more genes in common with one parent species, house sparrows
他们发现一些个体与一个亲本物种，麻雀有更多的共同基因
while others got more genes from their other parent, the Spanish sparrow.
而其他的则从另一种亲本种——西班牙麻雀那里得到了更多的基因。
In fact, different combinations of genes seemed to be more successful in different environments.
事实上，基因的不同组合四会在不同环境中更加成功。
Even Darwin's famous finches -- the birds he used to demonstrate incremental adaptations to different environments --
即使是达尔文著名的雀类—他用来证明对不同环境的适应性增强的鸟类—
seem to be able to hybridize with each other.
似乎能够彼此杂交。
And that genetic mixing may help drive their ability to rapidly adapt to changing conditions on the Galapagos islands they call home.
这种基因混合或许有助于它们迅速适应它们的家园—加拉帕戈斯群岛不断变化的环境。
So try as we might to create order in the universe by carefully categorizing and defining things, nature doesn't care about our definitions!
所以尽管我们努力通过仔细分类和定义事物来创造宇宙的秩序，大自然并不在乎我们的定义！
And while the biological species concept can be useful, evolution is a bit of a rebel.
虽然生物物种的概念可能有用，但进化有点叛逆。
And hybrids are material for evolution to work with.
杂交是进化的材料。
Thanks for watching this episode of SciShow, which was brought to you with the help of our patrons.
感谢收看本期节目，本期节目由我们的赞助人赞助播出。
Patrons get access to cool perks, including our very own patron Discord server,
我们的赞助人可以得到很酷的福利，包括我们自己的服务器，
and they make it possible for us to bring free educational videos to everyone.
并且它们使我们有可能为每个人带来免费的教育视频。
So thanks! If you want to join, head over to patreon.com/scishow.
所以感谢大家！如果你想加入我们，请前往patreon.com/scishow。
