Health

Health

Big brothers always have a lot to answer for

Having a big brother “cuts your chances of children” reports the Daily Mail today. It said that researchers believed the fertility of younger brothers or sisters could be affected by having an elder brother. The newspaper added that the phenomenon is thought to begin in the womb as “the physical cost of carrying a boy may take so much out of a woman that the health of her next child suffers”.

The story is based on a study that found that people with an older sister had a 67% chance of having children, compared to only 62% in people with an older brother.

However, the study was of three generations of Finnish people in the 18th and 19th century. There are many differences between present day UK and pre-industrial Finland, where there was a low life expectancy (23 years), high rates of death in childhood (only about half survived beyond 15 years), a relatively late age of becoming a father (26.7 years) and strict social monogamy (97% of couples having children were married).

Although the researchers say that their findings support a biological explanation, it seems equally possible that the slight difference in the chance of having children is due to social reasons, such as the bias shown towards a firstborn male child.