The evolution of animal genitalia - Menno Schilthuizen

譯者: Tammy Yuting Chiang 審譯者: Regina Chu

The evolutionary tango of animal genitalia.

動物生殖器官的演化探戈

Can you guess what you're looking at?

你猜得到你正在看什麼嗎？

If you answered "duck vagina," you'd be right.

如果你回答「鴨子陰道」 那就答對了！

Although the bird's outward appearance may not strike you as especially odd,

雖然鳥類的外型或許並不會 讓你覺得有什麼特別奇怪

it uses this strange, intricate,

牠們卻是運用像這樣

奇怪、複雜的 螺旋形器官來繁衍後代

cork-screw shaped contraption to reproduce.

We see similarly unbelievable genitalia in insects,

這般不可思議的生殖器 也能在昆蟲身上找到

mammals,

或是哺乳類

reptiles,

fish,

爬蟲類

魚類

spiders,

蜘蛛

and even snails.

甚至是蝸牛

Apparently, no organs evolve faster and into more variable shapes

顯然，其他器官的演化 都不如生殖器官這般迅速

than those involved in procreation.

這般多樣化

Superficially, it makes sense because evolution works via reproduction.

表面上，這很合理 因為演化即由繁衍而來

When an animal leaves more offspring, its genes will spread.

當一隻動物產下愈多後代 牠的基因就愈能遠播

And since genitalia are an animal's tools for reproduction,

由於生殖器官是 動物繁衍後代的工具

any improvement there will have immediate effect.

每當生殖器官有任何演進 便會隨即產生影響

And yet, what's the point of having such decorative nether regions?

但是，何必要有 這麼裝飾性的下體呢？

After all, the function of genitalia seems simple.

畢竟，生殖器官的功能 看起來終究簡單

A penis deposits a bit of sperm

陰莖產生一些精子

and a vagina receives it and delivers it to the egg.

陰道接收精子，並將精子傳送至卵子

A pipette-like thingy on the male

雄性提供滴管狀的東西

and a funnel-like gizmo on the female should do just fine for any animal.

雌性擁有漏斗狀的構造 在任何動物身上應皆能發揮作用

And yet, that's not what we see.

然而，事情並不全然那麼簡單

The penis of a chicken flea, for example, looks nothing like a pipette,

舉例來說，雞跳蚤的陰莖 看起來一點都不像滴管

more like an exploded grandfather clock.

反而像是一個炸開的老爺鐘

And the vagina of a featherwing beetle

至於羽翼甲蟲的陰道

resembles something you'd find in a Dr. Seuss book.

就好似某個在蘇斯博士的 繪本裡會看到的插圖

Throughout the animal kingdom,

在動物王國裡

genitalia are very complex things,

生殖器官其實是很複雜的東西

much more complicated than seems necessary for what they're meant to do.

遠比其看似簡單的功能更為複雜

That's because genitalia do more than just deposit and receive sperm.

因為生殖器官的作用 事實上不僅止於產生與接收精子

Many male animals also use the penis as courtship device, like crane flies.

對很多雄性動物來說 陰莖也是求愛工具，例如大蚊

In some South American species,

某些南美洲品種的大蚊

males have a tiny washboard and scraper on their penis,

陰莖上具有小型洗衣板和刮具

which produces a song that reverberates throughout the female's body

交配時，能夠演奏出曲子

when they mate.

在雌性的體內迴盪不絕

It's thought that if female crane flies enjoy this unusual serenade,

科學家相信，如果雌蚊 喜歡這首特別的小夜曲

they'll allow the male to father their offspring.

牠就會願意與該雄蚊產下後代

This way, the genes of the most musical penises spread,

如此一來，最具音樂性的 陰莖基因就會傳承下來

leading to rapid evolution of insects' phalluses.

促使昆蟲的陰莖快速演化

Similarly, some beetles have two little drumsticks on either side of the penis.

有些甲蟲的陰莖兩側 各有一枝小鼓棒，原理相似

During mating, they'll rub, slap, or tap the female with these.

交配時，雄性會用它們 摩擦、拍擊或敲打雌性

And some hoofed mammals, like rams and bulls,

部分有蹄類，包括公羊、公牛

use a whip-like extension on the penis's left side

其陰莖左側具有鞭子狀的延伸物

to create a sensation during mating.

能在交配時產生快感

But how can females really choose between males

但假如雌性只能在交配後 才能夠評判雄性優劣

if she can only assess them after mating?

那麼，牠們到底該如何選擇伴侶呢？

This is where the power of female adaptation comes into play.

這時候，雌性的調適能力 就要發揮其重要性了

In fact, insemination is different to conception,

事實上，受精並不等同於受孕

and the female genitalia exploit this distinction.

而雌性生殖器官 充分運用了此一差異

For instance, in some dung flies,

舉糞蠅為例

the vagina contains pockets for separating sperm from different males

其陰道具有多個口袋 能夠分裝不同雄蠅的精子

depending on how appealing they were.

雄蠅的個別魅力即為決勝關鍵

Males using their penises for courtship

雄性使用陰莖求愛

and females controlling their own sperm management

而雌性擁有自己的精子管理系統

are two reasons why genitalia evolve into such complex shapes.

以上兩個理由促使生殖器官 演化成如此複雜的形狀

But there are others

不只如此

because genitalia are also where a sexual conflict is played out.

由於生殖器官 也是性別衝突展現之處

A female's interests are best served if she fertilizes her eggs

雌性的利益唯有在以下情況 才能獲得最佳保障：

with the sperm of the best fathers

卵子受精自雄性伴侶最佳人選

and creates genetic variability amongst her offspring.

以及，為其後代創造遺傳變異性

For a male, on the other hand, this is bad news.

然而，這對雄性來說卻是壞消息

For him, it would be best if a female used his sperm

雌性最好只採用某單一雄性的精子

to fertilize all of her eggs.

來為所有的卵受精

So we see cycles of adaptation in an evolutionary arms race

因此，我們能看到一連串的 調適循環在演化過程中較勁

to retain control.

以爭取主導權

Black widow spiders have a disposable penis tip

黑寡婦擁有拋棄式龜頭

that breaks off inside the vagina blocking the attempts of his rivals,

會斷裂遺留在陰道中 阻擋其他對手精子的去路

and bed bug males bypass a female's genitalia altogether

而雄床蝨則乾脆略過雌床蝨的陰道

using a syringe-like penis to inject sperm cells directly into her belly.

用針筒狀的陰莖

直接將精子細胞注射進雌性的腹部

Not to be outdone,

雌床蝨也沒那麼好欺負

females have evolved their own countermeasures.

牠們演化出與之抗衡的對策

In some bed bug species,

在某些床蝨品種中

the females have evolved an entirely new set of genitalia

雌性演化出一整套全新的生殖器官

on their right hand flanks where the males usually pierce them.

位於腹部右側 也就是雄性經常刺穿的部位

That allows them to maintain the power to filter out unwanted sperm

如此一來，牠們就能夠 繼續運用生殖器官

with their genitalia.

篩選掉不要的精子

And duck vaginas are shaped like a clockwise spiral

至於鴨子的陰道 則呈現順時鐘螺旋狀

so that when the male inflates his long, counterclockwise coiled penis into her,

這樣一來，當公鴨將其 逆時針盤繞狀陰莖送進牠的陰道

and she disapproves,

但牠不同意的時候

all she needs to do is flex her vaginal muscles

牠只需要收縮陰道的肌肉

and the penis just flubs out.

陰莖就會被擠出來

So, genitalia differs so much, not just to fascinate us,

所以說，生殖器官如此多樣化 並非只是要讓我們驚豔

but because in every species,

更重要的是

they're the result of a furious evolutionary tango of sex

生殖器官是各物種性別間 激烈的演化探戈的成果

that has been going on for millions of years

這場探戈已經持續幾百萬年了

and will continue for millions of years to come.

並且還會繼續上演好幾百萬年