Summary

In Chapter 17, Bryson takes up with sexual organs and gender. Although a German researcher discovered chromosomes in the 1880s, scientists did not realize their significance until much later. Into the late 19th century, many scientists thought diet, air temperature or a woman’s mood determined the sex of a child. A German zoologist, Herman Henking, discovered the X chromosome in 1891. Nettie Stevens, who became a scientist late in life and received little credit for her work, discovered the Y chromosome. Chromosomes were difficult to study because scientists had to get samples from living cells at the moment of cell division. Biologists opted for some odd strategies like waiting at the foot of the gallows to obtain the testis of executed criminals. In 1921, a cytologist at the University of Texas said he had counted 24 pairs of chromosomes. That number stuck until...