Birth weight and survival in relation to natural selection
Rajanikumari, J.; Rao, T.V.
Anthropologischer Anzeiger; Bericht Uber die Biologisch-Anthropologische Literatur 45(2): 175-179
1987
ISSN/ISBN: 0003-5548 PMID: 3619416 DOI: 10.2307/29539782Document Number: 373139
Birth weight and perinatal mortality of 11,241 singleton infants born in the 2 hospitals of Viskhapatnam, Andhra Pradesh, South India were analyzed to compute the optimal birth weights, selection intensity and selective mortality by gender. The sex ratio was 97.4 males for 100 females. The mean birthweight were 2825.0 g for surviving males, 2091.1 for nonsurviving males, 2742.0 for surviving females and 1938.7 for nonsurviving females. Total perinatal mortality was 9.84% for males and 8.4% for females (p0.01). The optimal birthweights were 3252.9 and 3205.0 g, almost 475 g more than the actual means. Since the birthweights did not fit a Gaussian distribution, the formula of Sansing & Chinnici was used. Optimal birthweights were also computed with the quadratic model. The regression coefficients were 0.98 and 0.96 for males and females, but the curves were asymmetrical around the means. The parabolic fit of the natural log of survivors to nonsurvivors and birth weight suggests that a stabilizing form of selection is acting on birth weight. The selection intensity for male and female newborns was 0.693 and 0.0701. Selection curves were asymmetrical around the means, in an inverted "V" shape. There was a high degree of selection intensity in this series, with 74.76% of males and 81.18% of females less than optimal birth weight. 12.8% were low birth weight, weighing 2270 g. The selective mortality, i.e., the percent of selective deaths, was higher for female (79.55%) than male (65.82%) neonates. These data exhibit a highly negative selection intensity and selective mortality at the lower and higher birth weights than at intermediate weights, an example of stabilizing or centripetal natural selection.