Infants of a more medium weight survive much more often and the bell curve of the human population peaks at a birth weight that the newly born babies exhibit the minimum death rate. This is an example of

Stabilising selection eliminates individuals from both the extremes of a phenotypic distribution curve and more individuals acquire mean character value. Babies of low weight lose heat more quickly and get ill from infectious diseases more easily, whereas babies of large body weight are more difficult to deliver through the pelvis. Infants of a more medium weight survive much more often. For the larger or smaller babies, the baby mortality rate is much higher. The bell curve of the human population peaks at a birth weight that the newly born babies exhibit the minimum death rate.