性别决定：比你想象的更复杂：英语精读讲义

My wife is pregnant right now with our first child.

我妻子现在怀着我们的第一个孩子。

And when people see her with her big baby bump, 短語搭配

当人们看到她挺着大肚子时，

the first question people ask,

人们问的第一个问题，

almost without fail, 短語搭配

几乎无一例外，

is,

都是：

"Is it a boy or is it a girl?"

“是男孩还是女孩？”

Now,

其实，

there are some assumptions behind that question that we take for granted 講解

这个问题背后有一些我们理所当然的预设，

because of our familiarity with our own human biology. 短語搭配

因为我们对自身的人类生物学非常熟悉。

For human babies,

对于人类婴儿，

we take it for granted that there's a 50-50 chance of either answer, 用詞

我们理所当然地认为任何一种答案都有 50% 的几率，

boy or girl.

男孩或女孩。

But why is it that way?

但为什么会这样呢？

Well,

嗯，

the answer depends on the sex determination system 講解

答案取决于性别决定系统，

that has evolved for our species.

这是为了我们这个物种演化出来的。

You see,

你看，

for most mammals,

对大多数哺乳动物来说，

the sex of a baby is determined genetically 語法

婴儿的性别是由基因决定的，

with the XY chromosome system. 文化背景

使用的是 XY 染色体系统。

Mammals have a pair of sex chromosomes,

哺乳动物有一对性染色体，

one passed down from mom 短語動詞

一条来自母亲，

and one from dad.

一条来自父亲。

A pair of X's gives us a girl

一对 X 染色体会生出女孩，

and an X and a Y together gives us a boy.

一条 X 染色体和一条 Y 染色体则生出男孩。

Since females only have X's to pass on in their egg cells 短語動詞

由于雌性的卵细胞中只有 X 染色体可以遗传，

and males can give either an X or a Y in their sperm cells, 語法

而雄性的精子细胞既能提供 X 也能提供 Y 染色体，

the sex is determined by the father

所以性别是由父亲决定的，

and the chance of producing a male or a female is 50-50. 短語搭配

并且生男生女的几率各占 50%。

This system has worked well for mammals,

这个系统对哺乳动物来说非常有效，

but throughout the tree of life, 習語

但在整个生命之树中，

we can see other systems that have worked just as well for other animals. 短語搭配

我们可以看到其他动物也有同样有效的系统。

There are other groups of animals that also have genetic sex determination,

还有其他类群的动物也是由基因决定性别的，

but their systems can be pretty different from ours. 用詞

但它们的系统可能与我们的截然不同。

Birds and some reptiles have their sex genetically determined,

鸟类和一些爬行动物的性别是由基因决定的，

but instead of the sex being determined by dad, 語法

但它们的性别不是由父亲决定，

their sex is determined by mom.

而是由母亲决定的。

In those groups,

在这些类群中，

a pair of Z sex chromosomes produces a male.

一对 Z 性染色体产生雄性。

So,

因此，

these males only have Z's to give.

这些雄性只有 Z 染色体可以提供。

However,

然而，

in these animals,

在这些动物中，

one Z and one W chromosome

一条 Z 染色体和一条 W 染色体

together as a pair produces a female.

配对在一起会产生雌性。

In this system,

在这个系统里，

the chance of a male or a female is still 50-50.

产生雄性或雌性的几率仍然是 50%。

It just depends on whether mom puts a Z or a W into her egg. 語法

这只取决于母亲在卵子中放入 Z 还是 W 染色体。

Certain groups have taken genetic sex determination in completely other directions. 習語

某些动物的基因决定性别系统则走向了完全不同的方向。

Ants,

蚂蚁

for example,

就是一个例子，

have one of the most interesting systems for determining sex 語法

它们有着最有趣的性别决定系统之一，

and because of it,

正因为如此，

if you are a male ant,

如果你是一只雄蚁，

you do not have a father.

你其实是没有父亲的。

In an ant colony,

在一个蚁群中，

there are dramatic divisions of labor. 用詞

有着显著的劳动分工。

There are soldiers that defend the colony,

有保卫蚁群的兵蚁，

there are workers that collect food,

有收集食物、

clean the nest and care for the young, 用詞

清理蚁巢并照顾幼虫的工蚁，

and there's a queen and a small group of male reproductives. 用詞

还有一只蚁后和一小群负责繁殖的雄蚁。

Now,

接下来，

the queen will mate and then store sperm from the males. 用詞

蚁后会交配，然后储存来自雄蚁的精子。

And this is where the system gets really interesting. 表達脈絡

这就到了该系统真正有趣的地方。

If the queen uses the stored sperm to fertilize an egg, 語法

如果蚁后用储存的精子使卵子受精，

then that egg will grow up to become female. 短語搭配

那么这个卵就会发育成雌性。

However,

然而，

if she lays an egg without fertilizing it, 講解

如果她产下一枚未受精的卵，

then that egg will still grow up to be an ant,

这枚卵仍会发育成一只蚂蚁，

but it will always be a male.

但它永远是雄性。

So,

所以，

you see,

你看，

it's impossible for male ants to have fathers. 語法

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, 用詞

雄蚁的一生就只有每个基因的一个副本，

much like a walking sex cell. 習語

非常像是一个行走的生殖细胞。

This system is called a haplodiploid system

这个系统被称为单双倍体系统，

and we see it not only in ants, 語法

我们不仅在蚂蚁中能看到它，

but also in other highly social insects like bees and wasps. 用詞

在蜜蜂和黄蜂等其他高度社会化的昆虫中也能看到。

Since our own sex is determined by genes 表達脈絡

既然我们自身的性别是由基因决定的，

and we do know of these other animals that have their sex determined by genes, 語法

而且我们也知道其他一些动物的性别也是由基因决定的，

it's easy to assume that for all animals,

我们很容易就会认为对于所有动物而言，

the sex of their babies still must be determined by genetics. 語法

婴儿的性别一定也是由基因决定的。

However,

然而，

for some animals,

对某些动物来说，

the question of whether it will be a boy or a girl 語法

到底是男孩还是女孩这个问题

has nothing to do with genes at all 習語

完全与基因无关，

and it can depend on something like the weather. 短語搭配

反而可能取决于天气等因素。

These are animals like alligators and most turtles.

这些动物就包括短吻鳄和大部分龟类。

In these animals,

在这些动物中，

the sex of an embryo in a developing egg is determined by the temperature. 用詞

发育中的卵里胚胎的性别由温度决定。

In these species,

在这些物种里，

the sex of the baby is not yet determined when the egg is laid 語法

卵刚产下时婴儿的性别尚未决定，

and it remains undetermined 語法

并且会保持未决定状态，

until sometime in the middle of the overall development period

直到整个发育期的中间阶段，

when a critical time is reached. 用詞

也就是到了一个关键时期。

And during this time,

在这个时期，

the sex is completely determined by temperature in the nest.

性别完全由巢内的温度决定。

In painted turtles,

在锦龟中，

for example,

例如，

warm temperatures above the critical temperature 用詞

高于临界温度的温暖环境

will produce females within the eggs

会在卵内孕育出雌性，

and cool temperatures will produce a male.

而较低的温度则会孕育出雄性。

I'm not really sure who came up with this mnemonic, 短語動詞

我不太清楚是谁想出了这个记忆口诀，

but you can remember that when it comes to painted turtles, 短語搭配

但你可以记住，说到锦龟，

they are all hot chicks and cool dudes. 習語

它们都是“火辣的妹子和冷酷的小伙”（hot chicks and cool dudes）。

For some tropical fish,

对某些热带鱼来说，

the question of will it be a boy or will it be a girl

到底是男孩还是女孩的问题

isn't settled until even later in life. 用詞

直到生命更晚的阶段才会尘埃落定。

You see,

你看，

clownfish all start out their lives as males. 短語動詞

小丑鱼在生命之初都是雄性。

However,

然而，

as they mature, 語法

随着它们的成熟，

they become female.

它们会变成雌性。

They also spend their lives in small groups with a strict dominance hierarchy 用詞

它们也在小群体中度过一生，有着严格的等级制度，

where only the most dominant male and female reproduce.

其中只有最高等级的雄性和雌性才能繁殖。

And amazingly,

令人惊讶的是，

if the dominant female in the group dies,

如果群体中处于支配地位的雌性死亡，

the largest and most dominant male

体型最大、占支配地位的雄性

will then quickly become female

就会迅速变成雌性

and take her place 短語搭配

并取代她的位置，

and all of the other males will move up one rank in the hierarchy. 短語動詞

而其他所有雄性的等级也会随之上升一级。

In another very different ocean animal,

在另一种截然不同的海洋动物——

the green spoonworm,

绿叉螠（green spoonworm）身上，

the sex of the babies is determined by a completely different aspect of the environment. 用詞

后代的性别由环境中一个完全不同的方面所决定。

For this species,

对这个物种而言，

it is simply a matter of where a larva happens to randomly fall on the seafloor. 短語搭配

问题仅仅在于幼虫碰巧随机落在了海底的哪个位置。

If a larva lands on the open seafloor,

如果幼虫落在了空旷的海底，

then it will become a female.

它就会变成雌性。

But if it lands on top of a female, 短語搭配

但如果它落在了一只雌性的身上，

then it will become a male.

它就会变成雄性。

So,

所以，

for some species,

对某些物种来说，

the question of boy or girl is answered by genetics.

男孩还是女孩的问题是由基因解答的。

For others,

对另一些物种，

it's answered by the environment.

则由环境来解答。

And for others still, 表達脈絡

而对还有一些物种来说，

they don't even bother with the question at all. 習語

它们甚至根本不用为这个问题费心。

Take whiptail lizards, 表達脈絡

以鞭尾蜥蜴（whiptail lizards）

for example.

为例。

For those desert lizards,

对于这些沙漠蜥蜴，

the answer is easy.

答案很简单。

It's a girl.

是个女孩。

It's always a girl.

永远是个女孩。

They are a nearly all-female species 用詞

它们是一个几乎全是雌性的物种，

and although they still lay eggs, 語法

尽管它们仍然会产卵，

these eggs hatch out female clones of themselves. 短語動詞

但这些卵孵化出的都是它们自己的雌性克隆体。

So,

所以，

will it be a girl or will it be a boy?

到底是个女孩还是个男孩呢？

Throughout the entire animal kingdom, 表達脈絡

放眼整个动物界，

it does really all depend on the system of sex determination. 語法

这一切确实都取决于性别决定系统。

For humans,

对于人类来说，

that system is a genetic XY system.

这个系统是基因 XY 系统。

And for me and my wife,

而对于我和我的妻子，

we found out it's going to be a baby boy. 講解

我们发现我们将迎来一个男宝宝。