teri dei Delinquenti' and 'La Pubertà') has investigated the whole question of the influence of the age of the parent on the character of the child. He has found that when both parents are in the same period of age development elderly parents produce the highest proportion of 'very intelligent' children (though not the highest proportion of 'intelligent' children). Marro has also found that, taking the fathers alone, although 'intelligent' children are mostly the offspring of young fathers, 'very intelligent' children are mostly the offspring of middle-aged and elderly fathers. He finds much the same result as regards mothers. He found that the insane show an excess of elderly fathers, while murderers show a deficiency of young fathers and a very great excess of elderly fathers. The highest proportion of defectively intelligent children (this harmonizing with Langdon Down's results) Marro also found among the offspring of elderly fathers. Elderly fathers and very young mothers were found by Marro to produce the largest proportion; of 'good conduct' children, but not of intelligent children.
