The study of life (humans very much included) has not missed out in race to reduce. Our studies have borne much fruit. The realisation that DNA, inherited and reproducible, encodes our entire bodies has revolutionised our understanding. A natural conclusion of this might be that everything about us can be explained by our genes. Going back to our ‘onion’, we’ve peeled back all the layers to the core, found there a reel of programming, and then worked our way back out taking with us explanations for everything as we go. In some ways this is helpful and indeed true. In other ways it is hopelessly inadequate.
Take for example human behaviour. It is true that our genes do affect us and the way we act. We know this from twin-studies. Taking whole series of identical twins and seeing how their behaviour is similar or different to their brother or sister gives us a good idea of how much influence their shared genetic programmes have. What we find is that whilst the genes do have their say, they don’t have control. For some behaviour patterns there is a stronger genetic pressure than others, but the important thing to realise is that their effects are limited. They are only a fraction of the story.
Genes contain the programmes that have given us the bodies, and especially the brains, that in turn have given us permission to enter a whole new world, an unprecedented vista of culture, history, legacy, spirituality, morality and countless other things that when added together make us human. In these realms genes are like a parent unwilling to let go of a child though it has come of age. They still have influence but they’re limited, sometimes even powerless.
Suppose I were offered the position of Agony Aunt in my local paper (an unlikely scenario I know). In my new position I get asked by one heartbroken individual about why they were suffering so much in their love life. Would it be out of place of me to politely suggest that their problem is all down to their particular variant of the gene AVPR1A (known to be involved in pair bonding and relationship quality)? Or how about if I blame it all on their oxytocin levels? I don't think it would go down to well or even actually be of any help. Clearly, in these kind of situations reductionism doesn't work.
So, whilst we can gain much from breaking any complex subject down into its component parts - in many cases that isn't enough. Some scientist/philosophers fail to spot the difference.