I do know the answer about the sportsmen - basically, men in "high testosterone" jobs, like competitive sport, are more likely to have girls. I think it's because they make so much testosterone to do that and that makes their little Y-chromosomes not quite up to the job. The girly Xs can resist all that manly testosterone swilling around in there.

High testosterone women are more likely to have boys, low testosterone women girls (this is due to how hospitible the uterus is to the sperm). Hmm, looking at my blood tests that means I'm more likely to have boys. I think this is why some women seem to have only boys and others only girls, but lots of couples have a mix.

For non-stressy men, I don't think there's a big difference in the boy:girl ratio.

As for certain sex conceptions running in families: well, I'm the daughter of a daughter of a daughter of a daughter, and so back until the days of Eve; my husband is the son of a son of a son of a son (until the days of Adam) so I wonder what we'll have!

Also, let us not forget our statistics: there is a 1:2 chance of every child being a girl and a 1:2 chance of every child being a boy. If your first child is a girl, the chance of your next child being a girl is still 1:2 - just because you already got one, doesn't mean you will get something different next time. It's like flipping a coin twice: some people will get two tails, some two heads, others a head and a tail.

So the chance of having three boys is 1:8, but if you already have two boys your chance is 1:2 - assuming no other sperm-selection is used. Oh, I love probability!