>You don't have to be consciously aware that your uncle has a 1/4 chance of having any particular gene in your body
It's not a question of whether we're consciously or subconsciously aware. Without modern technology, we cannot be aware of genes at all; or said another way, we cannot be aware of whether somebody is REALLY our uncle. We can only go (generally subconsciously) on cues that will tend to be correlated with relationships, like similar features and habits, growing up with somebody (in the case of siblings or cousins), growing up to see someone as an authority figure (in the case of parents, uncles, etc), or raising someone (in the case of children —although for mothers, there is also bearing and nursing, which can create quite powerful ties).
In other words, our evolution-derived tendency to sacrifice for our kin MUST rely on a mechanism that can also lead us to sacrifice for our non-kin, because we have no way of detecting whether or not people are really kin or have merely filled an analogous role in our lives. Even a mother's tie to the children that she bears (which may well be so strong because it couldn't be faked) can now be invoked by merely surrogate motherhood (which can cause a lot of problems when a surrogate mother comes to love a baby that she agreed 9 months earlier to give up).
Most of the time, this falls short of altruism. Many people are quite willing to make small sacrifices for strangers, but most people would not sacrifice so much that you would call them altruistic. (And anyway, it's not really ‘altruism’ if it doesn't extend to everybody, which it usually won't.) But when communism (since this is a thread about communism) does work, and (as far as I'm aware) this is always on a small scale, I think that it does co-opt our innate tendency to help those like us, taking advantage of an ‘us against the world’ attitude.
>Most acts of kindness expect, if only implicitly, some reciprocation, however indirect it may be.
There are exceptions, but I'll agree with that for most acts. Of course, communist societies can take advantage of this too!