There is an old saying, “A bird in the hand is worth two in the bush”.  According to social science, this is more than a proverb.  It is true that our motives toward an aim are time indexed – the incentive we feel to on objective depends on our distance in time to its realization.  An example which illustrates this is: 


Suppose you had a choice between two plans a benefactor offers you, but you could not choose both.  On one plan, you will receive $500 in four years. On the alternate plan, you will receive $1000 in six years.  On these terms, it is predictable that most people will take the second plan rather than the first, since the expected utility is greater. 


On the other hand, suppose instead your benefactor offered you a choice between waiting two years to receive $1000 in two years or simply taking $500 now. On these terms it is predictable that most people will take the second option, even though the first has the greater expected utility, because they can think of immediate uses they can put the money to at the moment, or something like that.  The fact that this is actually predictable is what makes it seem that incentives are time indexed.  This is called “weakness of will”, not being able to choose what is in your best interests.  The view also seems to imply that there is no personal identity, since if we had an enduring personality, it would not have radically alternate priorities at different times.  To prevent weakness of will we have to behave now in such a way as to sabotage what our future selves will want to do.


It seems to me that there is perhaps a connection between weakness of will and the utility principle in the theory of evolution of species by natural selection.  According to the utility principle, only those features possessed by an organism that actually make a difference to its survival in its immediate environment are naturally selected for perpetuation.  If the feature does not contribute so, then it goes extinct.  Considering this along side of the predictability of weakness of will, it seems to show that expected utility calculation has never really played a role in our survival, that the needs of the moment have compelling power of what is in our long term best interests.  So given the utility principle and weakness of will, the ability to do expected utility calculations should have disappeared by now.


But given that expected utility calculation is flourishing in our society, there must be sources of explanation and causation that fall outside of the scope of natural selection. And they are most likely to be non-natural accountants.