Shouldn't there be more males than females? What am I forgetting about evolution? (cf breeders)

[LSLGuy]

That one has generated a couple of long threads with lots of “common-sense” handwaving about the huge effects and lots of math saying “Nope.”

It’s not up there with the 0.9999… = 1.0 or some of our other epic probability wars, but it’s close.

[DrCube]

@Leo_Bloom

fecundacity (can’t think of the word).

“Fecundity”.

[Leo_Bloom]

@HMS_Irruncible

Wild horse sex ratio is something like 43/57 in favor of females, according to a bit of Googling. If you are thinking that males should be overwhelmingly favored just because they can reproduce anytime, consider that about half of the father’s sperm actually codes for girl horses. (The mother always contributes an X chromosome, the father has roughly even chances of contributing an X or Y chromosome).

As to why the racetrack population seems skewed, it’s nothing to do with the birth rate, it’s just the fact that the faster horses tend to be male, so breeders send more males to the track.

Just as a side note (side bet) in my Kentucky Derby evolution model, it did not include the valuability of the offspring in The Great Game–males or females being desirable as winners wasn’t even in my mind; just the greater value in the Breeder’s/Leo’s Quondam God’s mind as a long term money-maker (which is the other, real Great Game for the lifetime of every player.

All this because of my dog, whose Uncle is showing in Westminster next week.

[Leo_Bloom]

Bump: Did I mention my dog’s Uncle is being shown at Westminster?

[Chronos]

Quoth markn+:

The answer, somewhat non-intuitively, is that it will have no effect. The sex ratio will remain at 1:1 despite the law, since every child born has an equal chance of being a boy or girl.

That depends on how long a run you look at. There are probably some people who are, for whatever reason, more prone to having one sex or the other. Absent that law, they’d naturally tend to occur in balanced numbers both ways. But with the law, people who are prone to having boys will tend to have more children than those who are prone to having girls. And so, if the tendency towards boys is heritable, over the evolutionarily-long run, the boy-biased folks will be favored, and will tend to make up an increasing proportion of the population.