My wife is pregnant right now with our first child, and when people see her with her big baby bump,
我的妻子正怀着我们的第一个孩子，当人们看到她挺着大肚子，
the first question people ask, almost without fail, is, "Is it a boy or is it a girl?"
第一个问题几乎总是，“是男的还是女的？”
Now, there are some assumptions behind that question that we take for granted
那么，这个问题背后有个前提，我们之所以不以为奇，
because of our familiarity with our own human biology.
是因为我们熟悉我们自己的人类生物学。
For human babies, we take it for granted that there's a 50/50 chance of either answer, boy or girl.
对人类婴儿而言，我们想当然认为有各半的机会其答案会是男生或女生。
But why is it that way?
但这是为什么？
Well, the answer depends on the sex determination system that has evolved for our species.
嗯，这答案与我们这个物种的性别决定系统有关。
You see, for most mammals, the sex of a baby is determined genetically with the XY chromosome system.
你看，对大多数哺乳类动物来说，婴儿的性别取决于遗传的XY染色体系统。
Mammals have a pair of sex chromosomes, one passed down from mom, and one from dad.
哺乳动物有一对性染色体，一条来自母亲，另一条则来自父亲。
A pair of X's gives us a girl, and an X and a Y together gives us a boy.
一对XX会得到女儿，而一条X及一条Y配对则得到儿子。
Since females only have X's to pass on in their egg cells,
既然雌性只有X可以传给卵子，
and males can give either an X or a Y in their sperm cells,
而雄性可以传X或Y给精子，
the sex is determined by the father and the chance of producing a male or a female is 50/50.
因而性别是由父亲决定的，而生产雄性或雌性的机会各半。
This system has worked well for mammals, but throughout the tree of life,
这个系统在哺乳动物内运作良好，但在整个演化树上，
we can see other systems that have worked just as well for other animals.
我们还看到其他系统在其它动物身上运作一样良好。
There are other groups of animals that also have genetic sex determination,
其他类动物也有遗传性别决定法，
but their systems can be pretty different from ours.
但它们的系统与我们的大庭相径。
Birds and some reptiles have their sex genetically determined,
鸟类及某些爬行类动物也有性别遗传决定法，
but instead of the sex being determined by dad, their sex is determined by mom.
但其性别不是由爸爸决定的，而是由妈妈决定。
In those groups, a pair of Z sex chromosomes produces a male, so these males only have Z's to give.
在这些动物内，一对ZZ性染色体会生出雄性，所以这些雄性只能给Z。
However, in these animals, one Z and one W chromosome together, as a pair, produces a female.
然而，这些动物如果是一条Z及一条W染色体配对，则产生雌性。
In this system, the chance of a male or a female is still 50/50,
在这样的系统里，生产雄性或雌性的机会仍是各半。
it just depends on whether mom puts a Z or a W into her egg.
仅在于母亲是放了一条Z还是一条W到卵子里。
Certain groups have taken genetic sex determination in completely other directions.
但某些种族则以完全不同的方法来决定遗传性别。
Ants, for example, have one of the most interesting systems for determining sex, and because of it,
举个例子，蚂蚁就有一套非常有趣的系统来决定性别，而且正因为如此，
if you are a male ant, you do not have a father.
如果你是只雄蚁，你没有父亲。
In an ant colony, there are dramatic divisions of labor.
在蚁巢里，每只蚂蚁的工作划分非常绝对。
There are soldiers that defend the colony, there are workers that collect food,
有兵蚁专门守御蚁巢，有工蚁收集食物，
clean the nest and care for the young, and there's a queen and a small group of male reproductives.
清理巢穴，并照顾幼蚁还有一只蚁后及一小群负责生殖的雄蚁。
Now, the queen will mate and then store sperm from the males.
那么，蚁后会与雄蚁交配并储存精子。
And this is where the system gets really interesting.
而这就是这系统有趣的地方。
If the queen uses the stored sperm to fertilize an egg, then that egg will grow up to become female.
如果蚁后拿储存的精子使卵子受孕，那么这个卵会长成一只雌蚁。
However, if she lays an egg without fertilizing it,
但是，如果它下了个未受精卵，
then that egg will still grow up to be an ant, but it will always be a male.
那这个卵子仍会长成一只蚂蚁，但会是只雄蚁。
So you see, it's impossible for male ants to have fathers.
所以你看，雄蚁是不可能有父亲的。
And male ants live their life like this, with only one copy of every gene, much like a walking sex cell.
而且雄蚁的一生就是这样，每一种基因都只有单个，就好像一个活生生的生殖细胞。
This system is called a haplodiploid system, and we see it not only in ants,
这个系统称作单倍双倍体性决定系统，而我们不只在蚂蚁上看到此现象，
but also in other highly social insects like bees and wasps.
也在其他高度群居昆虫，如蜜蜂及黄蜂上看到。

Since our own sex is determined by genes, and we do know of these other animals that have their sex determined by genes,
既然我们人类的性别取决于基因，我们的确也知道有其它动物一样由基因决定性别，
it's easy to assume that for all animals the sex of their babies still must be determined by genetics.
我们很容易假设所有的动物其婴儿的性别都是由基因决定的。
However, for some animals, the question of whether it will be a boy or a girl has nothing to do with genes at all,
但是，对某些动物而言，是男是女这个问题与基因一点关系都没有，
and it can depend on something like the weather.
反而被其它因素，如天气决定。
These are animals like alligators and most turtles.
这些动物包括鳄鱼或大部份乌龟。
In these animals, the sex of an embryo in a developing egg is determined by the temperature.
这些动物在蛋内发育的胚胎的性别，取决于温度。
In these species, the sex of the baby is not yet determined when the egg is laid,
这些物种在下蛋时，蛋内幼体的性别尚未决定，
and it remains undetermined until sometime in the middle of the overall development period, when a critical time is reached.
且会维持未定状态，直到大约胚胎发育中期这个关键时刻。
And during this time, the sex is completely determined by temperature in the nest.
在这段期间，其性别完全取决于巢内的温度。
In painted turtles, for example, warm temperatures above the critical temperature will produce females within the eggs,
以锦龟为例，如果温度超过这个关键温度，会使蛋孵出雌性幼体，
and cool temperatures will produce a male.
比较低的温度则产生雄性。
I'm not sure who came up with this mnemonic,
我不知道谁发明了这个助记法，
but you can remember that when it comes to painted turtles, they are all hot chicks and cool dudes.
但你可以这么记，就是说到锦龟，它们都是辣妹及酷哥。
For some tropical fish, the question of will it be a boy or will it be a girl isn't settled until even later in life.
对某些热带鱼而言，是男是女这个问题一定要到生命更后期才能回答。
You see, clownfish all start out their lives as males.
你看，小丑鱼在一开始都是雄性。
However, as they mature, they become female.
但是，成熟后都变成雌性。
They also spend their lives in small groups with a strict dominance hierarchy where only the most dominant male and female reproduce.
它们也一辈子活在小群体内，严格遵守阶级制，只有为首的雄鱼及雌鱼能繁殖下一代。
And amazingly, if the dominant female in the group dies,
而且很奇异的是，如果小群内为首的雌性死了，
the largest and most dominant male will then quickly become female and take her place,
其最大最具优势的雄鱼会很快地变成雌性并且代替她，
and all of the other males will move up one rank in the hierarchy.
然后其他雄性的地位都会向上提升一格。
In another very different ocean animal, the green spoonworm,
而另一种非常不一样的海洋动物，绿海洋蠕虫，则完全不同
the sex of the babies is determined by a completely different aspect of the environment.
其幼虫的性别由环境决定。
For this species, it is simply a matter of where a larva happens to randomly fall on the sea floor.
这种生物，就只看幼虫掉在海底哪里。
If a larva lands on the open sea floor, then it will become a female.
如果幼虫直接掉在海底就成了雌性。
But if it lands on top of a female, then it will become a male.
如果幼虫掉在雌性上面，就变成雄性。
So for some species, the question of boy or girl is answered by genetics.
所以对某些物种而言，是男是女由遗传决定。
For others, it's answered by the environment.
对其他物种则是由环境决定。
And for others still, they don't even bother with the question at all.
还有一些则根本不在乎这个问题。
Take whiptail lizards, for example. For those desert lizards, the answer is easy.
以鞭尾蜥为例，对这些沙漠蜥蜴而言，这答案很简单。
It's a girl. It's always a girl.
女生。永远都是女生。
They are a nearly all-female species, and although they still lay eggs, these eggs hatch out female clones of themselves.
这个物种几乎全是雌性，而且虽然它们也下蛋，这些蛋孵出来的只是复制的自己罢了。
So will it be a girl or will it be a boy?
所以是男是女呢？
Throughout the entire animal kingdom, it does really all depend on the system of sex determination.
整个动物界从上到下的确都有一套性别决定系统。
For humans, that system is a genetic XY system.
对人类而言，这套系统是遗传的XY系统。
And for me and my wife, we found out it's going to be a baby boy.
而对我及我的妻子而言，我们发现这会是个男宝宝。