The figure shows the ratio of no synonymous to synonymous po

The figure shows the ratio of no synonymous to synonymous polymorphism in humans and the ratio of no synonymous to synonymous substitutions between humans and chimpanzees. What do these data demonstrate about the nature of variation in human populations? Purifying selection is responsible for most synonymous differences between humans and chimpanzees. Much of the variation in humans is under purifying selection and therefore due to deleterious mutations. Humans have very few deleterious mutations and most substitutions are beneficial. Most of the variation in humans is due to balancing selection on beneficial mutations.

Solution

dN/dS=1 neutral evolution

dN/dS<1 purifying selection

dN/dS> positive selection

Synonymous change (silent change)
Nonsynonymous change ( replacement change) amimo acid change.

purifying selection is the selective removal of alleles that are deleterious. This can result in stabilizing selection through the purifying of deleterious variations that arise.

So answer is purifying selection is responsible for most synonymous differences between humans and chimpanzee