The income elasticity of marriage fidelity

Exercise

Apparently, a negative relation between the level of income and married fidelity exists: the frequency of infidelity, which is 50 percent for a man who makes 40,000 dollars a year, goe sup to 70 percent when his income increases to 70,000. Provide two explanations: economic and biological, and compare their predictive power.

----------------
The Economist, “Gentleman's Relish” (November, 25, 1989, p. 73).