What Do You Think You Are The Science of What Makes You You - Brian Clegg Page 0,20

example, assuming that maggots were spontaneously generated on rotting meat, tests were made with containers of the same meat, some open to the air, others sealed. The maggots only appeared in the open containers, showing that there was some external source of contamination – in this case, flies laying eggs – going unnoticed.

In trying to discover the nature of life, biologists tend to approach what it is from the top down, looking at organisms and trying to understand what makes them work. Physicists, though, have provided different insights into the way that flows of energy from place to place could produce life-like structures, or even help us to understand the origin of life itself.

THE LIFE THERMODYNAMIC

Generally speaking, there has been relatively little interaction between physics and biology. (It didn’t help that the great physicist Ernest Rutherford once made a cutting remark aimed at biologists’ focus on identification and classification that ‘All science is either physics or stamp collecting’.) However, a considerable contribution to our understanding of biology was made by Austrian quantum physicist Erwin Schrödinger. In 1944, Schrödinger published a book based on a series of lectures given in his adopted home of Dublin. What is Life? made energy flows central to the nature of life, along with a physical phenomenon called entropy.

Entropy is a feature of the second law of thermodynamics. At its simplest, this important physical law says that heat passes from a warmer body to a cooler body if they are in contact and no energy is put into the system.§ But the same law can also be phrased in a more interesting way that ‘entropy in a closed system stays the same or increases’. Entropy is a measure of the amount of disorder in a system.¶ This sounds a little fuzzy as a concept, but entropy is a precise mathematical construct, reflecting the number of ways the different components of the system can be arranged.

If you think of this book as a system, with the letters in it as its components, there is only one way to arrange the letters to make up the specific book that you are reading (ignoring swapping identical letters). There are vastly more ways to rearrange those letters to make something other than this book. Accordingly, the book has a much lower entropy than has the shuffled-up set of letters. And if you imagine that all the letters were loose on the page, it would be much easier with a quick shake to go from the ordered collection of letters in the book to a disordered mess of letters than it would to go from a scrambled up set of letters to the (hopefully) meaningful book.

Living organisms require a lot of structure and order – so have lower entropy than a random collection of the atoms that make them up. You may consider your life disordered, but in reality, there’s a remarkable amount of order required to make you out of those atoms. Schrödinger’s way of looking at life was as something capable of doing this – of using energy to push against the standard behaviour of the second law of thermodynamics.

In What is Life?, Schrödinger also made the suggestion that biological inheritance would depend on an ‘aperiodic crystal’ – a molecule that could carry information in its structure. This would be a crystal that instead of having the simple repeating structure we’re familiar with to form something like a salt crystal, has a far more complex structure that allows it to carry a whole string of information. This was a prediction that was fulfilled with the discovery of the structure of DNA. But the aspect of thermodynamics would later be revisited by physicists to suggest how life could have got started in the first place.

SOUP AND LIGHTNING

Before we get onto the thermodynamic approach, we can trace a more biologically driven exploration of the origins of life from the 1950s. If you’ve ever seen a film of Frankenstein, you will be familiar with the idea of employing the vast electrical power of lightning to give the initial kick required to bring life into being. Interestingly, in Mary Shelley’s original book, it’s not entirely clear that electricity was used in this way – it’s the 1931 James Whale version that gives us that classic image of the mad scientist harnessing the lightning bolts on a stormy night. It’s hard to believe that the movie wasn’t at least part of the inspiration for an experiment devised by Stanley Miller, a PhD student working