To Shakespeare’s Hamlet, we humans are “the paragon of animals.” But recent advances in genetics are suggesting that humans are far from being evolution’s greatest achievement.

For example, humans have an exceptionally high proportion of fertilized eggs that have the wrong number of chromosomes and one of the highest rates of harmful genetic mutation.

In my new book, “The Evolution of Imperfection,” I suggest that two features of our biology explain why our genetics are in such a poor state. First, we evolved a lot of our human features when our populations were small, and second, we feed our young across a placenta.