For which?

1) Does "for which" mean "because of which"?
2) Does "rationale" mean "theoretical base"?

Context:

The other main type of altruism for which we have a well-
worked-out Darwinian rationale is reciprocal altruism ('You
scratch my back and I'll scratch yours'). This theory, first intro-
duced to evolutionary biology by Robert Trivers and often
expressed in the mathematical language of game theory, does not
depend upon shared genes. Indeed, it works just as well, probably
even better, between members of widely different species, when it is
often called symbiosis. The principle is the basis of all trade and
barter in humans too. The hunter needs a spear and the smith
wants meat. The asymmetry brokers a deal. The bee needs nectar
and the flower needs pollinating. Flowers can't fly so they pay bees,