03 July 2007

Life: a Newtonian property of molecules?

Last week's Nature editorial tries to look on the bright side regarding 'cut and paste' manipulation of genes on a cellular level:

Synthetic biology's view of life as a molecular process lacking moral thresholds at the level of the cell is a powerful one. And it can and perhaps should be invoked to challenge characterizations of life that are sometimes used to defend religious dogma about the embryo. If this view undermines the notion that a 'divine spark' abruptly gives value to a fertilized egg — recognizing as it does that the formation of a new being is gradual, contingent and precarious — then the role of the term 'life' in that debate might acquire the ambiguity that it has always warranted.
The interesting bit of information at the heart of the editorial is that, contrary to what common sense would tell us, it's actually kind of difficult to find a bright-line test for aliveness at the cellular level. It's true, of course, that this ought to be a problem for those who believe that human life starts at conception. But advocates of the 'divine spark' position have had no problem resisting decades of data about fetal development indicating that, for whatever uniquely 'human' qualities one might define as central to the question, development of these qualities is always "gradual, contingent and precarious." It's unlikely that those committed to belief in the 'spark' will be troubled much by the additional complexity of deciding when a bundle of cells can properly be called 'alive.'

On a larger level, it seems that synthetic biology is positioned to do for the concept of 'life' what quantum mechanics did for the concept of 'physical reality.' Just as QM tells us that, way down on the subatomic level, physical reality breaks down into a set of wave functions and probabilities that just looks like the Newtonian world we think we inhabit, synthetic biology suggests that way down on a cellular level, life breaks down into a series of looped molecular processes that just looks like a 'spark of life.' Results: no bright-line test to distinguish matter from energy, or life from not-life. Which is fine and good, and fun to contemplate, but when was the last time you heard someone outside of a physics lab describing the world in terms of wave functions? Most non-physicist people, even people who accept the mathematical inevitability of QM, still perform their day-to-day thinking in terms of a classically physical universe, because it makes sense on the human scale. What's more, they believe in the physical universe, no matter what physics has to say. Similarly, even as people other than molecular biologists come to understand and accept a non-vitalistic, complexity-oriented view of life, it doesn't seem likely to become a big part of the public debate over things like abortion; it simply fails to fit into the human-scaled belief structure that almost all of us bring with us into ethics discussions.