Life from the cold, dark depths?


Creation: The Origin of Life / The Future of Life by Adam Rutherford (Viking)

Reviewed by Peter Forbes

Until recently, the most widespread hypothesis on the origin of life was that originated by Darwin: ‘But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts – light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes.’

This became more than inspired speculation in Stanley Miller's 1953 experiment in which electricity was passed through a mixture of common gasses to produce a few of the organic chemical building blocks of life. But, as Rutherford explains, a bolt of lightning might indeed have stirred a warm pond to produce a few proto-chemicals for life, but then there would follow … absolutely nothing. Rutherford explains why and outlines a viable alternative.

Creation: The Origin of Life is the latest attempt to popularise the theory that life evolved not in a warm pond but in the deep, cold ocean. This, originally the work of Bill Martin at the University of Dusseldorf, was elegantly outlined in Nick Lane's prizewinning Life Ascending, and also featured in Brian Cox's TV series Wonders of Life.

Students are taught that the vital attributes of life can be summed up in the mnemonic ‘Mrs Gren’: Movement, Respiration, Sensitivity, Growth-and-repair, Reproduction, Excretion and Nutrition. But we now know that there is a crucial missing factor – one that is the key to the origin of life: constant energy. You can't make a car go by exploding petrol in a cylinder once only. It has to keep on firing. So what were nature's primal fuel and spark plugs? The Lost City mid-Atlantic deep-sea vents discovered in 2000 are the best bet. Here, hot, mineral-rich fluids pour into a cold ocean where a rift opens between tectonic plates. They produce mineral chimneys with porous structures in which these energy processes could have become trapped in a micro-environment shielded from the open sea.

But energy gradients in themselves are not enough. In fact, there are three things that have to come together to produce free-living life-forms: the energy cycles that now power every living organism, a container cell and a replication process. The first life, according to Rutherford, may not have been cellular at all but merely the contents of cavities in these undersea chimneys. But at some point, the cell had to appear. This is the easy part of the mystery. Cell membranes, made of lipids rather like kitchen sink detergents, self-assemble readily in the laboratory. Rutherford has a nice analogy for this kind of self-organisation – he recommends observing a bowl of breakfast Cheerios which will spread across the surface of the milk to create a perfectly regular monolayer (although I think that mini-croutons on chicken soup illustrate the point better). Take phospholipid molecules with one water-loving end and one oil-loving and a sheet of them will automatically roll up into a hollow spherical ball, aka a cell.

But it's replication that causes the most problems. It used to be thought of as a chicken-and-egg problem: DNA makes proteins and DNA needs protein enzymes to replicate. So how did this ever start? But the most likely answer is neither chicken nor egg but rather a chegg or an ecken. RNA is an intermediary between DNA and proteins, but it can also replicate itself with no enzymatic assistance.

In the second book, Rutherford describes the ingenuity of research in pursuit of modified life-forms. The DNA/protein system of life is universal on Earth – just four bases in DNA and 20 amino acids in proteins. But biologists are now creating novel substances: DNA analogues with additional bases or a different sugar backbone – xeno-nucleic acids or XNAs. The antiviral drug acyclovir, for example, commonly used to treat cold sores, contains a novel synthetic base that gums up the viral works….

Peter Forbes's Dazzled and Deceived: Mimicry and Camouflage is published by Yale.

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