Amongst the general population it is widely held that it is possible to say how much of a characteristic is due to nature and how much is due to nurture. The thought in the background here is that some causes are more important than others. However, there is a longstanding consensus within biology that such talk is in fact meaningless. So what is going on here? One answer is that talk of causal importance should be understood in non-causal terms. I consider three possibilities of how this might be done. The second answer is that despite the consensus it is possible to weigh causes. I explore...