Abstract: The goal of human life is to purse happiness and no one would like to experience the pain. Many stimuli that afftcts happiness include food, marriage, friendship and companion, money and wealth and other factors. Both pursuing happiness and avoiding distresss can staisfy the need of happiness. Why do such simple things as eating our favorite foods when hungry, drinking cold water when hot and thirsty, bonding with our kin, having sex with our loved ones, being recognized by others, and achieving our goals after hard work make us happy? Why does failing to do any of these things make us distressed or unhappy? These experiences make us happy because, directly or indirectly, they have been linked to, and not having them has presented obstacles to, survival and reproductive success in our evolutionary past. The positive emotions collectively known as happiness are in turn selected by nature to motivate us to continue to pursue these fitness enhancing activities. So has the desire to seek happiness been selected to motivate living. An evolutionary psychological explanation of happiness focuses on the functions of the concerning experiences which are ultimately related to reproductive success including survival to reach reproductive success.

Key words: Happiness, distress, reproductive success, evolution, evolutionary psychology