Negro groups in West, Central and Southern Africa, also in Jamaica, have mean cardio-thoracic ratios significantly greater than those in corresponding age-sex groups of Caucasians.
To throw more light on the situation, studies on young and elderly Negroes have been made in certain groups in Southern Africa, also on local Caucasian groups. Only slight differences in ratio were found between local Negro groups, and Caucasian groups in South Africa, also in Wales and Tecumseh (U.S.A.). Yet ratios in Negro males from Malawi and Mozambique, resident in South Africa, were significantly greater than values in local Negroes. High ratios are not therefore invariable for Negroes. The difference observed relates to heart, not thoracic diameter. Since the phenomenon, which concerns heart position, is apparent in the young, almost certainly it is of ethnic origin. Investigations on cardiomegaly in African populations must take this factor into reckoning. Its presence or absence locally may readily be assessed by determining ratios in relatively small numbers of young people of both sexes.