Slightly off topic but the male/female ratio is very imbalanced in places. Having just moved back to Seattle from Tokyo, this imbalance is very prominent here, which wasn't noticeable in Tokyo. Just yesterday I went to a bar with a colleague. I counted 21 males, 0 females. That type of ratio isn't uncommon here it seems. A friend went to a yoga class with his girlfriend and he said more than half the class was male. They also took salsa lessons together and mentioned that men had to have other men as dance partners since there wasn't enough women to pair up with.

Seattle native here - this is only sort of true. Miami, LA, and Houston have a worse gender split[0]. My guess is that you're probably running in tech circles and hanging out in neighborhoods where locals don't live.

http://blogs.seattletimes.com/fyi-guy/2014/05/13/sorry-guys-...

Eh, I was an engineer in the bay area, and now a mommy in the bay area. I've seen the imbalance both ways in the exact same city. It's just a matter of your habits.

> They also took salsa lessons together and mentioned that men had to have other men as dance partners since there wasn't enough women to pair up with.

I wonder if this is mostly due to those men attending salsa classes hoping to meet women.

Hoping to meet women, or develop a talent/skill that they can use to impress women they meet elsewhere.

Yes.

What kind of bar was it?

In case you're not into skimming through the history, here's the nut graph:

"Any sex ratio much higher than 108 (52 percent male) at any time during pregnancy is essentially excluded by modern data. Past the middle of the second trimester the sex ratio is known with great accuracy, at least in industrialized countries with strong health systems and reliable vital statistics, because nearly every fetal death after that point is recorded. The sex ratio of 20-week fetuses is essentially identical to the secondary sex ratio: The numbers of deaths after that point is too small to make much difference, even if the stillborn were all male."

A note to the reader: this article has far more questions than answers. It's still interesting, but know what to expect before you read it. Unlike some, this author is very careful about understanding the limits of what we know.

It seemed to make a pretty strong statement by the end: "The old story of high primary sex ratio — as high as 282 (74 percent male) by some accounts — declining rapidly and then steadily to birth, is gone. Any sex ratio much higher than 108 (52 percent male) at any time during pregnancy is essentially excluded by modern data."

"Is the primary sex ratio the same in all human populations at all times?" At least the secondary sex ratio naturally varies in human populations, being lowest in African's and somewhat higher in most others, see [0] and many other references.

Meiotic drive can effect which embryo's survive [1] & [2]. It's an intragenomic conflict where one copy of a gene is passed on to offspring more than the expected 50%.

[0] http://www.cdc.gov/nchs/data/nvsr/nvsr53/nvsr53_20.pdf.

[1] https://westhunt.wordpress.com/2015/04/09/a-common-variant-l...

[2] http://www.unz.com/gnxp/human-uniqueness-is-not-unique/

I see a problem. They use data from in vitro fertilization to conclude the primary ratio is about 100. That's neglecting a part of the natural process that could introduce a bias. While earlier on the author rejects a couple of measurements due to their mutual inconsistency - even though they were both above 100.

I would say the ratio of boys to girls at the moment of conception is practically always 1:1?

The entire point of the article is that it isn't that clear.

No, the article is very clear that the ratio at conception is exactly 1:1 (or incredibly close to it).