Since this keeps getting batted around in a certain other thread. Two thoughts: 1) Asking how biology explains free will presumes there may be some reason to believe biology precludes free will (biological determinism or something). I don't think that's true. A counter question would be: why shouldn't a sentient biological organism have free will; and 2) When it comes to scientific explanations, it seems to me complexity and emergent properties are likely to play a role here. If you insist on a scientific basis for free will, that seems to me to serve as well as anything.