What shocked them was that, for the last decade,

他們震驚的原因是，在過去十年間，

Ispera's mother had been living only with other females.

Ispera 的母親一直只有與母鯊接觸。

But it's actually entirely possible that Ispera had no father—

但實際上，Ispera 非常有可能根本沒有父親。

and the reason why that is also explains other biological curiosities,

而這一原因也解釋了其他生物的奇妙之處，

like the existence of an all-female lizard species.

比如全雌性蜥蜴的存在。

Usually sexual species have sex cells that contain half the number of chromosomes required to create a viable embryo.

通常有性生殖物種的性細胞所含的染色體數，都是製造有效胚胎所需染色體數的一半。

So an egg cell must be fertilized by a sperm cell to form two full sets of chromosomes.

卵子得由精子受精，才能組成兩套完整的染色體。

But some species that have sex cells can undergo a type of asexual reproduction called parthenogenesis—

但有些有性生殖物種也能透過「孤雌生殖」無性繁殖。

meaning "virgin origin" in Greek.

此詞彙在希臘語中意為「處女生殖」。

In parthenogenesis, an embryo develops from an unfertilized egg cell that doubles its own chromosome count.

在孤雌生殖過程中，胚胎在未受精的卵子中發育，該卵子會自己複製染色體。

In fact, some animals only ever undergo parthenogenesis,

事實上，有些動物只會孤雌生殖，

while others can reproduce both sexually and parthenogenetically.

其他則可透過有性繁殖和孤雌生殖兩者繁殖。

It's actually more common than previously thought.

這其實比人們過去認為的更常見。

More than 80 different sexual vertebrate species—

80 種以上有性生殖脊椎動物，

including Komodo dragons and certain kinds of turkeys, pythons, and sharks—

包括科摩多龍、某些種類的火雞、蟒蛇和鯊魚，

have surprised us by occasionally reproducing this way.

都偶爾會以這種方式繁殖，十分驚人。

These discoveries were usually made when females unexpectedly gave birth in captivity.

這些發現通常是在雌性動物在被關著時，意外生下子嗣而產生的。

Ispera's birth, for one, may have been the first account of parthenogenesis in smoothhound sharks.

Ispera 的誕生可能是第一起星鯊孤雌生殖的案例。

Scientists also confirmed that parthenogenesis was taking place in some wild snake populations.

科學家們還證實了，一些野生蛇類也有孤雌生殖的情況。

But just how many fatherless creatures are running, slithering, and swimming around out there is unknown:

到底有多少沒有父親的生物在外奔跑、爬行、游行，我們不得而知。

it's a tough thing to track without population-wide genetic analyses.

如果不進行全族群遺傳分析就很難追踪。

So, why is it happening at all?

那為什麼會產生這種情況呢？

Scientists think parthenogenesis could be evolutionarily beneficial in some contexts because, well, sex can be a drag.

科學家們認為在某些情況下，孤雌生殖可能對進化有益，因為性有時挺拖後腿的。

Mating and its associated demands and rituals can be time and energy intensive,

交配及求偶很花時間和精力，

leave individuals vulnerable to predators, and even be fatal.

此時個體容易受掠食者攻擊，甚至喪命。

Parthenogenesis, meanwhile, requires only one parent.

而孤雌生殖僅需一名父親或母親。

Mayflies can sometimes default to parthenogenesis if there are no males available,

如果沒有雄性，蜉蝣有時會直接孤雌生殖，

which is especially handy because they've only got a day or so to reproduce before dying.

這特別方便，因為牠們只有一天左右時間能在死亡前進行繁殖。

It can also help rapidly expand a population.

這還可以幫助迅速擴大物種數目。

In the summer, when food is abundant,

在夏天，食物充裕時，

pea aphids can rely on parthenogenesis,

豌豆蚜蟲可依靠孤雌生殖，

allowing their population to explode under favorable conditions.

在有利的條件下爆炸性繁殖。

And in the autumn, they switch back to sex.

而到了秋天，牠們又轉回有性生殖。

But some aphids, katydids, lizards, geckos, and snakes only ever reproduce via parthenogenesis.

但有些蚜蟲、蟈蟈、蜥蜴、壁虎和蛇只會透過孤雌生殖繁殖。

So, why do other animals bother with sex?

那為什麼其他物種要承受有性生殖的麻煩呢？

Scientists hypothesize that sex makes up for its shortcomings with long-term gains.

科學家們假設，長遠來看，有性生殖的益處能彌補其不足之處。

It allows individuals to mix their genes, leading to greater genetic diversity.

這能混合基因，製造更多的遺傳多樣性。

That way, when the going gets tough,

這樣一來，當情況變得艱難時，

beneficial mutations can be selected and harmful ones can be removed without ending the entire population.

就能篩出有利個體，去除有害變異，而不會導致物種滅亡。

In a parthenogenetic population, on the other hand,

另一方面，孤雌生殖的群體中，

individuals can only reproduce using their own genetic material.

個體只能用自己的遺傳物質繁殖。

According to a theory called Muller's Ratchet,

根據「穆勒的制動齒輪假說」

that's not good.

這並不是什麼好事。

The theory predicts that parthenogenetic lineages will accumulate harmful mutations over time.

該理論預測，隨時間推移孤雌生殖物種會積累有害變異。

And eventually, after thousands of generations,

最終，經過幾千代，

will reach a point of so-called mutational meltdown.

將達到所謂的突變崩潰點。

At this stage, individuals will be so compromised that they can't reproduce,

在此階段，個體將嚴重損害到無法繁殖，

so the population will nosedive, leading to extinction.

導致物種數急劇下降，最終滅絕。

We haven't yet seen this entire process unfold in nature.

我們還沒在自然界中看過這整個過程。

But scientists have observed an accumulation of harmful mutations in parthenogenetic stick insects that are absent in their sexual relatives.

但科學家已在竹節蟲身上觀察到有害突變積累的情況，而這些突變在相近的有性生殖物種中並不存在。

Only time will tell whether this will cause their extinction.

只有時間才能證明這是否會導致其滅絕。

Otherwise, some parthenogenetic species appear to have ways of circumventing a mutational meltdown.

反之，有些孤雌生殖的物種似乎有辦法規避突變崩潰。

New Mexico whiptail lizards came about when two different lizard species hybridized,

新墨西哥鞭尾蜥蜴是由兩個不同蜥蜴品種雜交產生，

creating this new all-female species.

嶄新的全雌性物種就此誕生。

As hybrids, their genome is a combination of the different sets of chromosomes from their two parent species.

作為混血物種，牠們的基因是來自兩個親本物種的不同染色體組合。

This gives them a high level of genetic diversity,

這讓牠們的遺傳多樣性極高，

which may allow them to survive long into the future.

使他們更可能在未來長期存活下去。

Bdelloid rotifers, meanwhile, have been reproducing parthenogenetically for 60 million years.

而蛭態輪蟲六千萬年來一直都是孤雌生殖。

They might have managed this by taking in foreign genetic material.

牠們可能是通過吸收外來遺傳物質來存活如此之久的。

Indeed, about 10% of their genes comes from other organisms,

事實上，牠們的基因中約有 10% 來自其他生物，

like fungi, bacteria, and algae.

如真菌、細菌和藻類。

How exactly they do this is unclear,

我們仍不清楚牠們如何辦到的，

but whatever the trick is, it seems to be working.

但不管是什麼訣竅，似乎都起了作用。

To totally untangle the mysteries of reproduction,

為徹底解開生殖的神祕面紗，

we'll need more research—

我們仍需多加研究，

and probably a few more surprises like Ispera.

可能還需要一些像 Ispera 這樣的驚喜。