Subtitles section Play video
-
Most parents-to-be assumed that the sex of their child comes down to a flip of the chromosomal coin, with an equal chance at having a boy or girl.
-
But in reality, the odds aren't even.
-
For every 100 girls born, the world gains about 106 baby boys.
-
Currently that skewed sex ratio comes out to roughly ten million more baby boys than girls born worldwide each year.
-
There are some countries where human meddling stacks the odds even higher in favor of boys.
-
But that doesn't explain the fixed odds everywhere else.
-
The intrinsic boy-girl ratio is rigged by mother nature.
-
In fact, it's even more rigged than birth rates show.
-
Human conception results in about 150 male zygotes for every 100 females.
-
But there's a rather tragic reason for this big biological boy bias early on.
-
Male fetuses are much more likely to be miscarried or stillborn than female fetuses.
-
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.
-
So by the time kids grow up and reach baby-making age, the ratio of males to females is just about one to one.
-
But the likelihood of a boy even making it to birth is also influenced by his mom's living conditions during pregnancy.
-
For example, when a massive famine struck China in the 1960s, the relative likelihood of having a son suddenly dropped until the famine ended.
-
And male Americans born to billionaires seem to have higher than average odds of fathering sons.
-
Somehow, female biology suppresses boys' survival in the womb during tough times, and boost it when times are good.
-
We've seen same pattern in other mammals too.
-
When resources are scarce, mothers give birth to fewer males than normal.
-
When resources are plentiful, they bear more.
-
The best explanation we have for this has to do with sex -- the other kind
-
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.
-
Female offspring are almost guaranteed to reproduce, famine or no famine because male mammals are pretty much always willing to mate.
-
Males on the other hand have to compete for mating privileges.
-
A well-nurtured hunk has a good chance of mating with lots of females.
-
While a male weakened by famine might not score at all.
-
Some male offspring are a bigger risk in general. At all stages they're more likely to die.
-
And even if they live they might not reproduce.
-
But when times are good, boys' potential to father lots and lots of babies make them a biological risk worth taking.
-
Thanks to everyone who support us on Subbable.
-
Without you we literally couldn't continue to make these videos.
-
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.
