Summary

Bryson begins chapter 18 with a discussion of sperm, which he says are both the “astronauts of human biology” and “blundering idiots” because so few of them go on to fulfill their evolutionary purpose (289). The likelihood of fertilization from an act of sex is only 3 percent. From here, Bryson discusses fertility problems and lower sperm counts in the western world, although he also notes that many factors like diet and body temperature at the time of testing can affect measurements of sperm counts. Women have way more eggs than they use in a lifetime: about 180,000 total. Women receive all of their eggs in the womb. Bryson writes, “A twenty-week-old fetus will weigh no more than three or four ounces but will already have 6 million eggs inside her” (291). The quality of the eggs diminishes as the woman ages, but across...