Retorts

Abiogenisis and Evolution

I am prepared to agree with Renton Maclachlan [Retorts, July] in dividing the issue between us into two:

1: How did the earliest self-replicating entities arise? and

2: How do simple organisms evolve into more complex ones, and how do new features of life appear?

The answer to 2 is, by mutation and/or genetic mixing by sex, followed by natural selection. It is illogical of Mr Maclachlan to claim that because he thinks 1 is impossible, then 2 must also be impossible. The manifold examples of evolution are explicable by natural selection; I must again refer him to basic texts. The mechanism of mutation is now well understood at the molecular level (changes in DNA bases), and increased complexity can also be facilitated by gene duplication.

Mr Maclachlan asserts mutations are "degenerative" and "damaging". To refer in these terms to the acquisition of DDT-resistance by insects is anthropocentrism at its most extreme. To the insect this represents progress, enabling the species to survive in changed conditions otherwise lethal.

On 1, Mr Maclachlan derides my comment that scientists are "looking hard" for an answer. Lucky fellow, he knows the answer without having to look! Some of the "road blocks" he believes lie between the non-living and the living are now looking more circumventable. The abiotic synthesis of biological monomers was observed in the laboratory some decades ago, and astronomers are finding increasingly large organic molecules in space. Another "road block" is the linking of such monomers into the biopolymers, nucleic acids and proteins. I refer readers to recent work from Orgel's laboratory, demonstrating just such synthesis on the surface of minerals. Polynucleotides and polypeptides up to 50-mers were made; these are into the size range of informational macromolecules on which life depends.

I challenge Mr Maclachlan to set out and justify his idea of a minimum replicator. His emotional conviction of what is and is not possible is anti-scientific. Such an attitude rules out any enquiry before one could start.

Professor Bernard Howard, Christchurch