Individuals homozygous for PKU allele cannot metabolize phenylalanine, a component of many proteins. Result Severe mental retardation if they eat a normal diet. As a result this behavior will be favored by natural selection. The description of the behavior may not be correct. Many psychologists think rape in humans is an aspect of violent or aggressive behavior, not an aspect of sexual behavior.
Biological principles describe the way the world is .
Ethical principles describe the way the world ought to be .