In the English upper and upper-middle classes, the prevalence of first-cousin marriage had remained steady at between 4% and 5% for much of the 19th century. However, after the First World War, there was a sudden change, and cousin marriage became very unusual.

Are 1st cousins allowed to marry?

Depending on your culture, cousins marrying cousins will either be a normal occurrence or something hugely taboo. Here in Britain its actually perfectly legal for first cousins to marry. Prince Philip and The Queen are even third cousins. Charles Darwin was also married to his first cousin Emma Wedgwood.