Why Do Middle-Age Men Cheat?

Christopher Ryan and Cacilda Jethá continue to plug their book on the evolution of human sexuality. On infidelity:

With the caveat that every situation is different, one factor we think deserves more attention is the role of testosterone(T) in middle-aged men's eroticism. In their twenties, men's T levelsbegin a long decline, often experienced as diminished passion and appetite for life. Suppressed T levels are associated with depression, heart attacks, dementia,and overall mortality rates...