Yes, but that's to save River. He'd give up his life for hers in a second. Or at least he would have, until Jubal threatened raping Kaylee too.

I've always wondered, considering kin relationships and species survival when looking at evolutionary biology (some animals will sacrifice themselves to give the advantage to related animals because it best preserves their genes in the long run) if that didn't come into play a bit here. Just subconsciously.