Observed behavior is likely to have developed because it is adaptive. It has been naturally selected, i.e., individuals who are best adapted survive and reproduce. Behaviors may even be sexually selected, i.e., individuals who are most successful in gaining access to mates leave behind more offspring. The mind is therefore equipped with ‘instincts’ that enabled our ancestors to survive and reproduce.
A strength of this approach is that it can explain behaviors that appear dysfunctional, such as anorexia, or behaviors that make little sense in a modern context, such as our biological stress response when finding out we are overdrawn at the bank.