Letter: Life, but not as we know it

From Paul Newell

I find the definition of life as a “self-sustained chemical system capable of undergoing Darwinian evolution,” a surprising one to have gained credence (18 November, p 46). Darwinian evolution can refer only to a group of entities, and indeed many generations thereof. As such, if I were the last human in existence, I would not be considered as “life” by this definition as I would no longer be capable of Darwinian evolution. GM crops which produce sterile seeds would be further examples of non-life.

The mistake that has been made is to constrain all possible forms of life by the definition of the only example we know of. I can envisage a planet where a freak occurrence in its sea of chemicals gives rise to a complex cellular system. The system grows by a mechanism akin to cell division, but every cell is the same as the last. Change is not necessary, for it resides in a nutrient-rich, stable environment with no competition. Existence is a cinch. After millions of years it covers more than half of the planet’s surface.

Maybe one day it will cease to exist because it will have consumed all available resources. Is this system undergoing Darwinian evolution?

No. Is it alive? Of course.

It’s not hard to envisage such life, and many other wackier examples.

So, it’s not hard to realise that Darwinian evolution has no place in a definition of life.

Shepton Mallet, Somerset, UK