It seems to me that these discussions about human nature are treating
nature and "the social" as falsely dichotomous. Human self interest is
a product of psychic dislocation from the whole of nature and
integration into the human social network through language acquisition.
Self awareness is not even possible without socialization--as G. H. Mead
points out among a slew of others--so surely "self interest" is also a
social by-product. However, this process of individuation is a truly
"natural process" in the sense that there is no "human being" without
it. That is, there are no human characteristics present in unsocialized
homo sapiens; in them resides human potential only.
Of course the obvious implications from this brief (very brief) sketch
is that this discussion of self interested rationality reveals itself as
a paradox; and a historically contingent one at that. Our nature is
only "self interested" if one accepts the fact that our nature is
ultimately social. For if the social system were one based on the
material necessity of cooperation then surely we would observe a much
different type of "self interest", yet, because of the socialization
process which appears to me to one or "ego-building or individuation"
humans would still be self-interested even if this manifest itself in
some type of "group first" orientation.
This also points out the necessity of "unpacking" the concept of self
interest. It is used in a variety of analytic and ideological forms.
The defintion currently used by "classical economists" and rational
choice theorists is nothing more than antiseptic-capitalist ideology
which obscures the systemic imperative for accumulation; which would
more rightly be called "greed". This posting is clearly not to offer an
exhaustive or theoretically rigorous answer to the human conundrum; it
is rather meant to be suggestive of a way of thinking about it.
Cheers,
Christian