Do people do what they perceive to be in their best interest?
Yes. One basic trait of all individuals is self-interest. We are interested in protecting our close family and ourselves. Why?
Since natural selection is about survival and reproduction, and individuals either survive or die and reproduce or not, it makes sense that individuals are predisposed to act in ways that enhance their own prospects for survival and reproduction. The ancestral environment consisted of limited resources, including reproductive resources. Self-interest came naturally.
What if our ancestors were composed of altruists – individuals that helped others at their own expense? Altruistic individuals are at a disadvantage. They are always vulnerable to some mutants that advantage of them. Altruistic behavior cannot evolve by natural selection since natural selection favors success. Only behavior that is selfish or for the mutual good is in an individual’s self-interest and therefore favored by natural selection. Some behaviors may under certain circumstances look like altruism but can often be explained by self-benefit. Social recognition, prestige, fear of social disapproval, shame, relief from distress, avoidance of guilt, a better after-life or social expectations are some reasons behind “altruistic” acts.
The love of approbation and the dread of infamy, as well as the bestowal of praise or blame, are primarily due…to the instinct of sympathy; and this instinct no doubt was originally acquired, like all the other social instincts through natural selection…We may therefore conclude that primeval man, at a very remote period, would have been influenced by the praise and blame of his fellows. It is obvious, that the members of the same tribe would approve of conduct which appeared to them to be for the general good and would reprobate that which appeared evil. To do good unto others – to do unto others as ye would they should do unto you, - is the foundation-stone of morality. It is therefore, hardly possible to exaggerate the importance during rude times of the love of praise and the dread of blame. A man who was not impelled to by any deep, instinctive feeling, to sacrifice his life for the good of others, yet was roused to such actions by a sense of glory, would by his example excite the same wish for glory in other men, and would strengthen by exercise the noble feeling of admiration. He might thus do far more good to his tribe than by begetting offspring with a tendency to inherent his own high character.
It must not be forgotten that although a high standard of morality gives but a slight or no advantage to each individual man and his children over the other men in the same tribe, yet that an advancement in the standard of morality and an increase in the number of well-endowed men will certainly give an immense advantage to one tribe over another.”