My sister's keeper

摘要

Twin brothers can leave quite an impression. The mere presence of a boy in the same womb as his sister causes her to develop bigger teeth than she otherwise would. Girls with twin brothers perform better on spatial-ability tests. They have better ball skills than most females; squarer, more masculine jaws and are more likely to be short-sighted. Now it seems that sharing the womb also has a deleterious effect on the sexual reproduction of women with a twin brother.