Prenatal and Early Postnatal Influences

may be related to the selective advantages of maturity at birth, particularly, in man, the development of immunity to infectious disease. Verbal reasoning scores recorded in the 11-plus examination provide no evidence that the retarded prenatal growth associated with prolongation of gestation affects measured intelligence. There are considerable score differences in a general population of births in relation to birth weight and duration of gestation; but, like the larger differences related to maternal age and order of birth, they are not found in sibs. Still more suggestive is the finding that twins raised singly from birth have