A reminder that Darwin was not merely drawing up a list of the advantages and drawbacks of marriage before deciding to wed, but following the ideas of Benthamism then in vogue, and specifically Jeremy Bentham's schemes of "moral arithmetic"

The Darwin archive holds an amusing sheet of paper on which he sets out the pluses of having a wife, such as tasty cooking and domestic cosiness, and the minuses, such as having to be friendly with a mother-in-law and putting up with a woman in his own house.

In the end the pluses outnumbered the minuses, and Darwin married his cousin Emma; they remained married for 43 years and brought 10 children into the world