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Hey there! Welcome to Life Noggin.
大家好！欢迎观看脑洞大开的生命奇想。
There is a species of whiptail lizard in which every single lizard is female.
有一种动物叫鞭尾蜥，这个物种每一只蜥蜴都是雌性。
There are no males to mate with, yet their species lives on.
虽然没有雄性与雌性交配，这个物种依旧存活下来了。
And this is because these lady lizards reproduce asexually, creating offspring that are genetic copies of themselves.
这是因为这些雌性鞭尾蜥无性繁殖，繁育的后代是自己的基因复制品。
And this is pretty efficient!
这样效率太高了！
I mean, if your goal is to have offspring that carry on your genes, if you reproduce asexually, your offspring is 100% you.我是说，如果你的目标是繁育后代传播基因，如果你可以无性繁殖，你的后代就是另一个你。
However, if you reproduce sexually instead, your offspring is a mix of your genes and your mate’s, not just yours.
但是，如果你有性繁殖，你的后代就是你和你伴侣的基因混合体，不只是你自己的基因。
And not to mention, in an all-female species, there would be more offspring since every member would be able to reproduce.
更何况，在全都是雌性的物种里，每个成员都可以生育，因此后代会越来越多。
So why doesn’t every species, including humans, reproduce asexually?
为什么不是所有物种都可以无性繁殖？为什么人类不可以无性繁殖？
The simple answer is because of genetic variation.
答案很简单：基因变异。
See, the inefficiency of reproducing sexually is overcome by the benefits of combining your genes with another person’s.
有性繁殖效率不高，但是将你的基因和另一个人的基因结合在一起了。
To explain why, let’s go over two concepts: Muller’s ratchet and the Red Queen Hypothesis.
这是为什么呢？我们来看两个概念：缪勒氏齿轮和红皇后假说。
Suppose there is a species of animal that has some type of harmful mutation.
假设有一个物种发生了有害的基因突变。
These are very common and in a small population, it is likely that every individual has at least one.
这是很常见的，而在数量少的物种中，很可能每个个体都携带一种基因突变。
Assuming there is no back mutation, if that species reproduces asexually, there is no way that mutation can be removed.
假设没有回复突变，如果这个物种是无性繁殖，那么这种基因突变就无法消除了。
So, any offspring will have the same mutations as its parent.
每个后代都会和母体有同样的基因突变。
In later generations, as more mutations occur, every individual may have at least two mutations, or three, and so on.
随着物种繁衍，基因突变越来越多，每个个体可能至少携带两种突变，或者三种，或者更多。
And like turns of a ratchet, these mutations will accumulate until the species eventually becomes extinct.
像齿轮旋转一样，这些突变逐渐累积起来，最后整个物种灭绝。
But for species that reproduce sexually, this may not be the case.
但是有性繁殖的物种，就没有这种风险。
Members of these species will still have deleterious mutations, but their offspring may not.
这些物种的成员也会发生有害突变，但是不会遗传给后代。
To put it simply, during meiosis, the process in which gametes are created, chromosomal crossover occurs.
简单来说，细胞分裂的过程中产生配子，发生染色体互换。
This is when an individual’s chromosomes, which are are inherited from each of the parents, cross over one another, enabling genes from one chromosome to swap places with genes from another.
这时，一个个体从亲本双方遗传的染色体，与另一个会发生互换，最终一个染色体中的基因会和另一个染色体中的基因互换位置。
As a result, the recombined chromosome is genetically different from the ones there originally.
然后，重新组合的染色体就和起初不一样了。
And therefore, some of the harmful mutations may not be present in the offspring, even though they were present in the parent.
因此，亲本的许多有害突变就不会出现在后代身上。
Next, we have the Red Queen Hypothesis, which gets its name from, you guessed it, the Red Queen from Through the Looking Glass.
下一个是红皇后假说。你可能猜不到，它的名字来源于《爱丽丝镜中奇遇记》中的红皇后。
See, in the book, in one of the dreams that Alice had, she is running after the Red Queen, but discovers that neither of them are actually moving.
在这本书里，爱丽丝做了一个梦，梦见她追着红皇后跑，最后发现其实她们两个都没动。
So, how does this have to do with sexual reproduction?
那么这跟有性繁殖有什么关系呢？
Well, let’s imagine that there is a host and a parasite.
想象一下，一个宿主和一个寄生物。
The host species may evolve to become resistant to the parasite.
宿主这个物种要进化，以抵抗寄生物。
But for the parasite species to not go extinct, it needs to evolve to cope with the change in the host.
而寄生物为了延续种族生命，也需要进化，以适应宿主的变化。
Now, evolution is a slow process, but sexual reproduction can help speed it up.
进化是一个缓慢的过程，但是有性繁殖可以加速进化。
This is because it introduces new, potentially beneficial, mutations faster than asexual reproduction.
因为与无性繁殖相比，有性繁殖能够更快地引入新的基因突变，这个基因突变有可能是有益的。
So, if both species reproduce sexually, they can continue “running” like Alice and the Queen, while staying in exactly the same place...aka not going extinct.
所以，如果两个物种都是有性繁殖，他们可以像爱丽丝和皇后一样“你追我赶”，最后结果是原地踏步，也就是不会灭绝。
Sure, it would be cool to have an exact copy of yourself, but you may eventually be able to do that with cloning instead. Ok, that's enough. No seriously. That's too much.
当然，有个自身的复制品好像很好玩，但是真的想要这样的复制品的话，可以采用克隆的手段。好了够了！开玩笑的，太过分了。
Let me know in the comment section below what we should talk about next. We are taking suggestions for new videos.
请在下方评论区告知我们今后视频的话题。我们正在为新视频征集建议。
If you want to know more about sexual education, please check out our good friend Laci Green.
如果想进一步了解性教育，清点击我们的好朋友洛奇·格林的视频。
She dominates sex ed here on YouTube, and you should definitely watch her latest video exploring the truth about herpes.
她是油管上性教育的人气播主，你可以点击她的最新视频了解疱疹的真相。
Make sure you come back every Monday for a brand new video.
每周一都要回来看新视频哦~
There’s a link in the description if you’re on mobile.
手机观看，可以点击描述区的链接。
As always, I’m Blocko and this has been Life Noggin.
我是宝高，这里是脑洞大开的生命奇想。
Don’t forget to keep on thinking!
思考不要停！
