As has been said, it depends alot of the individual situation.
I don't think self defense is selfish at all. But I do think it is
a form of survival. I think part of what justifies it though, is
summed up in one word: retribution. A justified punishment
as consequence to ones choice of action. To threaten or
harm another for what is rightfully thiers is wrong. In many
cultures it is considered a crime worthy of death.
If someone is willing to threaten or even murder myself or
my loved ones for what we have, then they may do it to
others too. Thus there could be a civic duty to protect thier other
potential victims from being murdered as well.
AS to other situations, lost in the wild, ship wreck, etc:
Someone else mentioned that leaving another person behind is
in a way killing them. While I do agree that not saving them
does imply a lesser chance of thier survival, to suggest that
it's your, or my, job to save everyone is nonsense. I believe it is
every adult persons' own responsibility to train, learn and prepare.
It is thier own responsibility to decide thier priorities and
if survival had been one of them, then they should have made
more effort to be ready, and to do so. If they did not for whatever
reason, that is thier problem, and thier fault. Not mine.
Nor will I feel any guilt or shame for not saving them.
Now if saving them is something I can do without significant
risk to my own(or my loved ones') well being, then I will.
I'm not heartless. But if saving them means a major risk to
my own survival, hey, sucks for them.
I also think that it may be fair to say that alot of the altruistic
ideals people place on survival situations are illogical.
The idea that letting the strong die off first to save the weak
seems kind of silly. If they were too weak to survive on
thier own, then how are they gonna survive once you're
dead and no longer there to baby sit them?
As someone else mentioned, if the baby bear dies, momma
bear can have another baby bear. If momma bear dies,
so do all her babies, present and future.
Self sacrafice can be noble and beautiful in the
movies with fancy music and pretty sunsets,
but in reality it seems to be more detriment than
benefit.
If you wanna call it selfish, fine. Maybe selfish
makes a stronger more responsible people.