Thursday, 6 September 2007

The Meaning of Life? Or, Why Definitions Are Important...

Larry Moran points to a new article by Carl Zimmer that's up over at Seed, on the search for definitions of life. A lot of space in it is devoted to Carol Cleland, a philosopher, and Christopher Chyba, an astronomer, who argue that

the search for a definition of life is beyond problematic, and we should simply stop looking for one. The quest could either be impossible or scientifically trivial.
They compare the search for definitions of life to alchemy in the middle ages:
Cleland and Chyba also determined that there was an even bigger problem with the pursuit of a definition of life—one that lies in the nature of definitions themselves. "If you really understand what a definition is," says Chyba, "it's not up to handling the problem... ...scientists who try to define life today make the same mistake that alchemists did in the Middle Ages. Alchemists tried to define substances by their properties, without any understanding of the underlying chemistry. Water, for example, was defined according to its ability to dissolve different solids. This definition led alchemists into confusion. Since ice couldn't dissolve anything, it couldn't be water. Alchemists gave the name "water" to things that we know now are nothing of the sort. They called nitric acid aqua fortis, or strong water, because it could dissolve most metals. Aqua regia, or noble water, was actually a mixture of hydrochloric acid and nitric acid that was powerful enough to dissolve even gold and platinum, the so-called noble metals.

Searching for a better definition of water would have not gotten alchemists out of this mire. A solution only came in the 18th century, as scientists formulated a theory of chemistry. The behavior of water and other substances suddenly makes a lot of sense when you realize that they are all composed of atoms, which are in turn composed of smaller particles. Chemists can now say water is H2O. However, "'Water is H2O' isn't a definition," says Cleland. "It's a discovery."

So what's the remedy? To forget about definitions and build a 'theory' of life, apparently. How will we do that?
For Cleland, the most promising way to build a theory of life is to look for alien life. In 2013, the European Space Agency plans to put a rover back on Mars. Called Exomars, it will drill into the Martian crust to seek out signs of life. NASA has plans of its own on the drawing board, including one possible mission that would bring Martian soil back to Earth for intense study. Meanwhile, other promising habitats for life, such as some of the moons of Jupiter and Saturn, beckon. Cleland argues that finding alien life would allow us to start figuring out what is truly universal about life, rather than just generalizing from life as we know it. Only when we have more data, she reasons, will we have a basis for comparison. As it stands now, says Cleland, "we have no grist for the theoretical mill."
I agree more data is vital, but to me their trivialising of the need for a definition is entirely the wrong way round. Looking for alien life to gather more information on what life is is all well and good, but it presumes that we will be able to recognise it as life. And how will we do that? Either we will simply look at it and say 'That's life', in which case we already have an implicit definition, or we will have an explicit definition we compare it to to decide whether it is life or not. And this is where their analogy with the discovery of H20 falls down. Alchemists had another 'alien' form of water right in front of them: ice. They couldn't recognise it, however, as their definition of water was faulty - they had defined it as something that could dissolve things. How was progress made? Well, they looked further into the matter and realised everything is composed of atoms - they then applied this knowledge to water as defined by the old definition, realised ice was identical to it and subsumed both substances within a new definition referring to H20.

I submit that science progresses by defining things, examining them, applying this new knowledge to the old definition to make a better definition, and so on, ad infinitum - a 'virtuous circle', if you will. But the vital point is to make any headway, you need to kick start the circle - you need some kind of definition, no matter how bad, to decide what it is you're actually talking about. So to say 'the whole definition project is worthless.' is far from the truth. The definition project is of imperative importance: however, we don't need to have a perfect definition at the first try. Let's not agonise for ages for it. Let's just grab the most reasonable one we have now off the shelf, plug it in to science's 'virtuous circle', and sit back and admire the results.


Christopher Taylor said...

An awful lot of time has been wasted in the past because people failed to realise that they were using different definitions. Take the "evolution happens very slowly" vs. "evolution can happen very quickly" debate that surrounded Punctuated Equilibrium. A lot of unnecessary heat came out of people failing to realise that a "long time" for an ecologist might be a "short time" for a geologist. Definitions are critical.

Ben D said...

Exactly. That's why the denigration of the need for definitions irritates me so much. If you can't settle on a definition there's not much else you can do!