Originally posted by dj2becker
How do you know this? Has it ever been observed or is it simply a theory?
That which helps an organism survive and reproduce remains in the gene pool and proliferates. Those random events which are detrimental to this end disappear from the gene pool.
Take a look at the section of this website titled "Genetic Changes Over Generations":
http://anthro.palomar.edu/evolve/evolve_3.htm
An experiment in which a petri dish of bacteria is exposed to an antibiotic is described. Those bacteria with the genes that make the bacteria immune or resistant to the antibiotic thrive under the new conditions, while those bacteria which are genetically vulnerable die off. Therefore, this part of my post has been observed. The TOE predicted the phenomenon of resistance to the chemicals we use to kill pests and disease causing organisms.
Happiness and pleasure as well as pain and suffering are consequences of those activities and qualities which work towards the end (or against, in the case of pain and suffering) of survival and reproduction in general.
Injuries and disease cause pain and suffering. Rejection from society causes pain and suffering. Being rejected by someone you love causes pain and suffering.
Being healthy causes happiness. Eating fatty, sugary, and sweet foods causes pleasure, and these things help people survive long enough to reproduce when food is scarce. Exercise brings feelings of pleasure.
This correlation has been observed.
Also observed have been where pleasure was detrimental and pain beneficial, but these examples as a whole are exceptions to the general rule. As the TOE predicts, organisms are not perfect and often in conflict with one another. For example, those drugs which humans did not synthesize and which cause pleasure are products of other life and used for the purposes of that life. Human synthesis of drugs helps the drug makers by giving them wealth even when it causes problems for the users.
As logic helps me attain that which brings happiness and avoids pain, I trust it.
Logic has helped me be at peace with death. It helps me attain the goals I set for myself. It explains nature exceptionally well. Technology is a result of logic, and it's given a tremendous amount of humanity enough to eat, protection from natural disasters and enemies, etc such that more people can reproduce and survive. The value of logic has been observed.
So what I described is a theory. The evidence for this theory has been very much observed. The answer to your second question is 'both'.