[Jedd]

Darwin's family history is fascinating -- the intertwining with the Wedgewoods (as you note, Charles and Emma were first cousins), but doubtless exacerbated by the frequent first-cousin marriages in Emma Wedgewood's recent ancestry.

Darwin was aware of the risks of inbreeding, and this marriage in particular, expressing those concerns in various writings.

They had 9 or 10 children, IIRC, with 3 or 4 of them dying in childhood, and only a couple going on to produce a further generation. (Not so uncommon these days, but at the time I believe this was quite noteworthy.)

[auganov]

Such a rate of childhood death would be high even for sibling parents. So perhaps there was something else going on.

[bzbarsky]

> Such a rate of childhood death would be high even for sibling parents.

Really? In the mid-19th century?

https://ourworldindata.org/child-mortality/ says "in 18th century Sweden every third child died, and in 19th century Germany every second child died" (that's before the age of 5; the usual definition of child mortality). The "England and Wales" chart on that site shows that in the mid-1800s child mortality was about 250-300 per 1000.

So out of 10 children you would expect 2-3 to die before reaching age 5 at the time.

If you look at https://en.wikipedia.org/wiki/Charles_Darwin#Children there were 10 children. Their ages at death are:

74, 10, 1 month, 84, 67, 78, 77, 93, 77, 18 months.

So two deaths before age 5, one death at 10, the rest living to perfectly reasonable ages. Doesn't seem at all unreasonable for the time period.

[auganov]

Thanks, didn't at all realize how bad it used to be :O Even today it seems to be much worse than I'd naively assume.

[bzbarsky]

Yeah, historically people had lots of kids not least because lots of them would not survive...

As for today, child mortality in developed countries is well less than 1%. And most of that is infant mortality (death before age 1). For example, http://apps.who.int/gho/data/view.main.CM1320R (sorry, somewhat slow) shows that in the US in 2015 infant mortality was 5.6 per 1000, while child mortality was 6.5 per 1000. Neonatal mortality (death within 4 weeks of birth) was 3.6 per 1000.

And a lot of that is preterm births; for full-term births the US rate of infant mortality is closer to 2.5 according to http://www.webmd.com/baby/news/20091103/preemies-raise-us-in...

(Insert here rant about how different countries report some of these numbers differently, with some counting a 21-week birth followed by death a day later as a miscarriage, some counting it as a stillbirth, and some counting it as a live baby that died. As the mortality numbers drop these edge cases matter more and more. Obviously back when child mortality was in the mid-double-digit percentages these edge cases were not really important.)

What was your naive assumption about child mortality rates, if I might ask?

[auganov]

I don't remember having a concrete number in my mind. I guess I'd assume .1% for today. Had a picture of it as "something that's very tragic and basically doesn't happen anymore". While .5% puts it into the "not likely but might happen to you" range.

And as for a century and two ago I'd be waaaaaaay off base. Probably 10% or even 5%. It's hard to say in the hindsight. Now it seems so obvious and makes you feel stupid.