The graph below shows the birthweights and infant mortality rate as recorded by researchers in London between 1935 and 1946. The bars represent the number of births recorded in 0.5-pound increments. The orange dots represent the mortality rate for each birthweight and are shown on a logarithmic scale. What type of selection does this graph suggest directly affects human birth weight?
Graph adapted from: M.N. Karn and L.S. Penrose, Birth Weight and Gestation Time in Relation to Maternal Age, Parity, and Infant Survival. Annals of Eugenics, January 1951, Vol. 16 No. 1., Page 147-164.