Law and explanation in biology: Invariance is the kind of stability that matters

This paper develops an account of explanation in biology which does not inv olve appeal to laws of nature, at least as traditionally conceived. Explana tory generalizations in biology must satisfy a requirement that I call inva riance, but need not satisfy most of the other standard criteria for lawful ness. Once this point is recognized, there is little motivation for regardi ng such generalizations as laws of nature. Some of the differences between invariance and the related notions of stability and resiliency, due respect ively to Sandra Mitchell and Brian Skyrms, are explored.