Stephen Buranyi misses some key points in his article (Do we need a new theory of evolution?, 28 June). Darwin saw novel speciation as resulting from natural selection acting on anatomical variants, but that simple skeleton needed fleshing out. It took a century of research, for example, for us to understand the importance of inheritance in very small populations if novel variants were to become predominant.
The major problems in understanding evolutionary change today are as follows. First, working out how anatomical variants form – and this is hard because we don’t yet have a full understanding of how normal embryology works (evolution, it has been claimed, is development gone wrong) and can only rarely recognise a favourable mutation. Second, unpicking the generally opaque processes of selection (there are at least four independent reasons why zebra stripes would be favoured). Third, understanding why substantial evolutionary change seems so slow, albeit that this is what the fossil record demonstrates. This is the topic that excites the community that Buranyi discusses, even though modern molecular genetics and systems biology show that heritable novelties can form more rapidly than they realise.
The deeper problem is that evolutionary change involves the complete scale of nature, from DNA mutation to climate change, so of course there can be no unifying theory. The difficulty for scientists is that convincing experimentation is hard and slow.
Prof Jonathan Bard
Oxford
• Those biologists who are critical of current Darwinian orthodoxy and who want to modify the theory in the direction of the “extended Darwinian synthesis” need to take things further. They need to recognise that all living things are purposive. They pursue goals – without necessarily being aware of it – the ultimate goal being survival and reproductive success.
Purposive action can, in a multitude of ways, influence what has survival value – and thus influence the future course of evolution. Purposive action that results in living in a new environment, or pursuing new kinds of food, can change what has survival value for that creature and its offspring, and thus can influence the future course of evolution. Foxes hunting rabbits breed rabbits better able to escape; and rabbits escaping breed foxes better able to catch them.
Above all, when animals make discoveries and learn from one another, cultural evolution becomes possible, and that can have a massive impact on subsequent evolution, as the case of human evolution, and the evolution of language, show.
We need a new, unified version of Darwinian theory that recognises that the purposive actions of living things play a vital role in evolution. This is very definitely not Lamarckism, although too many biologists have denied the Darwinian role of purposive action in evolution for fear that that commits one to Lamarckism. For more about this, see chapter 6 of my 2020 book Our Fundamental Problem: A Revolutionary Approach to Philosophy.
Nicholas Maxwell
Emeritus reader, science and technology studies, University College London
• Surely there’s no problem with having several conflicting theories of evolution? Eventually the fittest will survive.
Pete Bibby
Sheffield
