But in reality, the odds aren't even.

但事實上，機率是不一樣的。

For every 100 girls born, the world gains about 106 baby boys.

每當有 100 個女孩出生時，相對會有 106 個男孩出生。

Currently that skewed sex ratio comes out to roughly ten million more baby boys than girls born worldwide each year.

目前這樣失衡的性別比例，造成全球每年出生的男嬰比女嬰多出約 1,000 萬個。

There are some countries where human meddling stacks the odds even higher in favor of boys.

有些施行人工干預政策的國家男嬰比例甚至更高。

But that doesn't explain the fixed odds everywhere else.

但這不能解釋世界上其他地方的固定機率。

The intrinsic boy-girl ratio is rigged by mother nature.

真正的男女比例是源自於大自然。

In fact, it's even more rigged than birth rates show.

事實上，自然的男女比例比目前的生育率更不平均。

Human conception results in about 150 male zygotes for every 100 females.

人體受孕的結果大約是 150 個男性受精卵比上 100 個女性。

But there's a rather tragic reason for this big biological boy bias early on.

但在早期，大自然安排男性受精卵比率比較高，是有相對的悲慘原因。

Male fetuses are much more likely to be miscarried or stillborn than female fetuses.

男胎比起女胎更容易流產或是死胎。

And boys that do make it out of the womb suffer more fatal diseases, take more mortal risks and fall prey to more violence than girls.

相較於女孩，男孩出生後較易感染致命疾病，也承擔更高的道德風險，並容易淪為暴力的犧牲品。

So by the time kids grow up and reach baby-making age, the ratio of males to females is just about one to one.

所以當孩子成長到可以生育的年齡時，男女比例大概就是一比一。

But the likelihood of a boy even making it to birth is also influenced by his mom's living conditions during pregnancy.

但是男孩出生的可能性也與母親懷孕時的生活條件相關。

For example, when a massive famine struck China in the 1960s, the relative likelihood of having a son suddenly dropped until the famine ended.

例如，中國在 1960 年代發生大饑荒，男孩的出生率急劇下降，直到饑荒結束才恢復。

And male Americans born to billionaires seem to have higher than average odds of fathering sons.

而含著金湯匙出生的美國男性，生出兒子的機率似乎高於平均值。

Somehow, female biology suppresses boys' survival in the womb during tough times, and boost it when times are good.

不知何故，母體在環境艱困時會抑制男孩在子宮內存活，在環境好時則相反。

We've seen same pattern in other mammals too.

其它哺乳類動物也有相同的情況。

When resources are scarce, mothers give birth to fewer males than normal.

當資源缺乏的時候，母親生下的男胎比平常少。

When resources are plentiful, they bear more.

當資源充足的時候，就會生下更多孩子。

The best explanation we have for this has to do with sex -- the other kind

這個論點最適合用性行為來解釋。

In biological terms, the whole goal of copulation is to reproduce to pass on your genes to someone who will someday pass them on again.

從生物學的角度，交配的目標就是為了繁殖，將自己的基因一再延續下去。

Female offspring are almost guaranteed to reproduce, famine or no famine because male mammals are pretty much always willing to mate.

女性的後代幾乎是繁殖的保證，不論有沒有饑荒，因為雄性哺乳類動物往往很樂於交配。

Males on the other hand have to compete for mating privileges.

另一方面，男性也需要競爭來取得交配權。

A well-nurtured hunk has a good chance of mating with lots of females.

一個威爾納的獵人，他很有可能廣受女性歡迎。

While a male weakened by famine might not score at all.

而一個飢餓無力的男性則一點機會都沒有。

Some male offspring are a bigger risk in general. At all stages they're more likely to die.

某些男性後代通常承受較大的風險，在生命各階段的死亡率都比女性高。

And even if they live they might not reproduce.

而即使他們活下來了，可能也無法傳宗接代。

But when times are good, boys' potential to father lots and lots of babies make them a biological risk worth taking.

但當狀況好的時候，男性有潛力生下非常多的孩子，那麼從生物學上來看，男性存在的風險也許利大於弊。

Thanks to everyone who support us on Subbable.

謝謝大家支持 Subbable。

Without you we literally couldn't continue to make these videos.

沒有你們我們就無法繼續製作這些影片。

If you aren't yet a supporter of MinuteEarth and want to become one, head over to subbable.com/minuteearth to make a one-time or monthly pledged support and thanks for watching.

如果你還不是 MinuteEarth 的支持者，而你想成為支持者的話，去 subbable.com/minuteearth 並且做單次或每月的支持吧！謝謝收看。