From Henry Webber
Michael Le Page tells how all life on Earth derives from LUCA, the last universal common ancestor (16 August, p 30).
It seems odd that life originated only once. Why has a different biochemistry not begun to evolve in parallel during all these billions of years? Was the emergence of prokaryotic and then eukaryotic cells so vanishingly improbable that the chance has not recurred?
It seems likely that other workable biochemistries are possible. Is it possible to put numbers to these evolutionary probabilities? Doing this might indicate something about the chances of life existing elsewhere in the cosmos.
Oxted, Surrey, UK
