1. Jet lag describes the fatigue and disorientation that result from flying across many time zones. What causes jet lag, and how does the body eventually adjust to a new time zone? Why is there no...

1. Jet lag describes the fatigue and disorientation that result from flying across many time zones. What causes jet lag, and how does the body eventually adjust to a new time zone? Why is there no such thing as “train lag” or “bicycle lag”?

2. How has natural selection acted on testosterone levels in men? Is there an ideal testosterone level for all phases of a man’s life?