Pretty much what it is for every trait shaped by evolution - does it make the species more successful and able to reproduce?
Humans weren't as fast or strong as many of our early competitors so the groups that learned to socialize and work together were more successful.
Moral codes, particularly the many manifestations of the Golden Rule, are just a codification of what experience shows us works.
I know you want a metaphysical discussion but that's not what evolution addresses.
Evolution theory has effected philosophical changes on society, and no other kinds of changes. It has had zero effect on the products of hard science. As such, there is no dependence whatsoever of science on the philosophy that is evolution theory.
Related to this, all discussions of evolution are either primarily philosophical in nature, or they exist exclusively in a context that is mostly philosophical.