Tracing genealogies has become immensely popular of late, and numerous companies offer to help you search through historical records or analyze your DNA. The pastime is no doubt enlivened by the scintillating possibility that you might discover noble blood, or even a notorious rogue, hiding in your family tree. But such discoveries generally don’t tell the searcher much; most of us have little idea of how our genes are bequeathed to us at all.
Carl Zimmer’s interest in genetic inheritance began when his wife, Grace, was pregnant with their first child, and the couple met with a genetics counselor. Zimmer, who has written books on evolution, neuroscience, and bacteriology, didn’t see the point of the meeting, for they had already decided to have the child regardless of any genetic flaws that might be found. It was only when the counselor asked the couple about their family histories that Zimmer realized how little he knew about his own, and began to be curious about his ancestry.
The result, many years later, is both two delightful, healthy daughters and She Has...