Fraternal asymmetry

Small body asymmetries are thought to be the result of the problems faced by the developing foetus, such as a mild infection in the mother. The more older brothers a man has, the more likely he is to show random asymmetries in his body shape. It is thought that male foetuses trigger an immune reaction in their mothers, linked to antigens produced by genes on the Y chromosome. Each successive male child would boost that response.
(F) Fuzzy exceptional problems