In former writings on this subject, especially in the "Edinburgh Medical Journal" for January 1872, I have insisted on the purely mechanical nature of this disease; that it is like a dislocation or a hernia; that, if hypertrophy favours its production, it is by the increase of weight it implies; that, if relaxation or laceration of tissues favour its production, it is by removal or diminution o...

Historical data from Finnish populations reveals that, for females, exposure to a male twin in the womb may have significant, life-long, effects on subsequent fitness, with profound implications for the evolution of sex ratios and brood size.