Parental stature and birth weight.

IN 1938 Walton & Hammond described the results of reciprocal Shire-Shetland crosses effected by artificial insemination. They showed that the weight of the foal of Shire dam and Shetland sire was about the same at birth as that of the foal of pure Shire parents, and the weight of the foal of Shetland dam and Shire sire was no greater than that of the foal of pure Shetland parents. Numbers of observations were very small, but the differences exhibited were so striking that it can hardly be doubted that the weight of the foal at birth was more highly correlated with the weight of the dam than with the weight of the sire. Walton & Hammond attributed this result to the uterine environment, and noted that after weaning "foals from the Shire mares (Shetland sires) grew much less rapidly than pure Shire foals, and the foals from the Shetland mares (Shire sires) grew much more rapidly than pure Shetlands". In rabbits, similar results were reported by Robb (1929) on data provided by Castle who crossed Flemish Giant and Polish breeds. Hybrid animals from Giant does and Polish bucks were almost as large at birth as pure bred Giants; unfortunately Polish does and Giant bucks were not mated. Differences in growth rate were exhibited after birth, and the weight of mature hybrid animals was about midway between weights of the pure breeds. In man, correlations between size of parents and size of offspring at birth have been examined by Lenner (1943), who found only trivial differences (a) between correlations of birth weight with mother's weight (0.19) and birth weight with father's weight (0.18), and (b) between correlations of birth length with mother's height (0.20) and birth length with father's height (0.21). When corrected for height of the other parent correlations were lowered slightly, but still indicated that the size of the child at birth is about equally affected by the size of each parent. A preliminary inspection of a somewhat larger series of our own gave a different result, more consistent with the observations derived from the ShireShetland cross. We have therefore examined more exhaustively correlations at birth, and in the two years after birth, between the size of a child and the size of its parents. In another communication (McKeown & Record, 1954) we enquire to what extent these correlations are modified by changes in the prenatal environment, in particular those associated with litter size and birth order.