Cuckoos and Peppered Moths – how natural is selection?

Cuckoo. Cheating by Nature – Nick Davies, Bloomsbury, 2015

Of Moths and Men. An Evolutionary Tale: The Untold Story of Science and the Peppered Moth- Judith Hooper, 2002

There is a long history of the inferential use of natural history observation , and the fascination it creates for the observer and reader. Gilbert White (reverend)and his correspondents allow themselves to speculate , and to reinforce their belief in the Great Design.  Others set out to look for some kind of proof of phenomena  – I think of Fabre‘s  laborious experiments  imposing repetition  and variation on his hunting wasps;this tradition eventually sinking into the confident personification of animal intent that permeates the voice-over of countless ‘nature programmes’.


The cuckoo book is in the Fabre tradition, sometimes known as ethology,  written by a  field scientist working on the nearest cuckoos to Cambridge . It has the essence of a species monograph , which spills over into the more popular science and natural history genres.

It is about cuckoos, but it is , of course, also about how to situate reporting the work of scientists into a more popular market. This it does well, and the conundrums of the evolution of cuckoo behaviour, and what Davies’, following Darwin,  characterises as an’ arms race’ with their hosts, led me back into the theory of natural selection again.


In fact to the extent that it came to haunt and dominate my response to the book.

I remembered a doubt I have always had about a view of natural selection which sees it as purposive, and directional . This is invoked by the famous phrase about the ‘survival of the fittest’, which was originally developed as a Victorian apologia for human suffering , and enthusiastically adopted by Darwinians (and at times by Darwin).

In another form – and this is where Cuckoo goes- it gives us to believe that  all evolved characteristics probably have some useful purpose. For example here is Davies explanation of the different plumage morphs in cuckoos

 Variable plumage is characteristic of other species of parasitic cuckoo too, and is likely to have evolved to confuse enemy recognition by host

and again on how host species recognise their own eggs

An obvious way of avoiding this mistake would be to imprint only on the first laid egg.This would ensure the host learned what its egg looked like before any cuckoo had a chance to lay. This would work beautifully if there were no variations in the hosts own eggs.. If a females eggs were variable however, then she would need to prolong learning.. The best compromise may be to prolong learning until the host has been exposed to a rangeof its own general learning should be more prolonged the more variable the host’s own eggs and the lower the chances of parasitism. Experiments are needed to test these ideas



A cuckoo in the Museum of Scotland demonstrates that being out of focus is an adaptive disguise..

I might quickly point out that experiments are indeed needed, but they would show what happens – not why it does. Or they might show what can happen now – but not how that came to pass. And in most  real life situations there are too many variables to control to make more than an impressively thorough Just So Story.

How did the Peppered Moth lose its Sprinkle..

Then I stumbled across Of Moths and Men  in the local library. My ecology degree is dated , but I recognised many of the names inside – Ford, Kettlewell, Haldane, Huxley , Lewontin , Jay Gould, without being able to place them in connection to each other in the history of science. ( I notice I am keeping to the convention of enumerating the scientists by surnames , like footballers, which is slightly awkward since many of them in a process of natural selection, have  given birth to other scientists…)

The book is about crypsis , hiding things, overtly, peppered moths.. proximately, flaws in evidence , and ultimately, a critique of scientific method, which flowed from the pen of Thomas Kuhn in the 1960s, and I found immensely helpful in an unreformed science department in the 1980s.


Melanism in the peppered moth was believed to be supported and encouraged by the selective predation on a more common morph on the altered bark of sooty trees in industrial areas of the UK. This was a reasonable hypothesis , given both the rapid spread of a black melanistic form  through the industrial revolution and the development of the synthesis between natural selection and genetic theory . A group of scientists and mathematicians  in Oxford had founded a branch of science called ecological genetics , and sought proof  of how these type of changes might occur.
An experimental trial by a researcher in the team appeared to show selective predation by birds on white forms in polluted areas , and black forms in non-polluted, and to a degree which implied that it was statistically sufficient explanation for the spread of the black, melanistic form.


So conclusive that it appears( ed) in most scientific textbooks as the supporting proof of natural selection – partly because of its clear premise and experimental design (and partly because there were few convincing alternatives). I was rewarded for reproducing it in various biology exams.

It still feels a shock to find out it is not true . As the book carefully demonstrates, the experimental design was repeatedly altered to reflect the bias of the researcher, moth and bird behaviour were effectively manipulated in the trial, and the results were smoothed in such a way that they are statistically impossible.  Aspects of the findings produced scepticism , initially from lepidopterists, and then successively from statisticians, evolutionists and ethologists, up to the present.  However even within the book the most critical biologists are unwilling to say it was fraudulent or even wrongly premised.

an adaptationist programme has dominated evolutionary thought in England and the US during the past forty years. It is  based on faith in the power of natural selection as an optimising agent. It proceeds by breaking an organism into unitary traits and proposing an adaptationist story for each considered seperately


Initially , the book suggests, this was because it was released as a foundation of how evolutionary genetics could take place, and currently , as it is a pedagogic prop to the teaching of evolution, under attack by creationists, and by university governments moving towards more lucrative cellular views of biology. Criticising the paradigm leaves you open to these attacks, and damages your own reputation – I mean, the Scottish Education Department might even rescind my Higher Biology..


The book advances ( somewhat slowly) towards its  argument through the prism of the personalities of a group of charismatic but insecure scientists, participating in their own survival of the fittest around academic tenure, reputation and legacy… Some of these are charicatures, maybe scurillous ones, and have upset the colleagues of the deceased scientists. They have in turn strongly criticised Hooper’s research , but do not seem to have produced repudiations of the flaws she has pointed out in the experiment and its subsequent promotion*.


EB Ford s school  of ecological genetics ( which apparently was never formally recognised as a university department) was the initial victor , and paradigm setter, but was quickly and successfully challenged  by the more stochastic ideas of Stephen Jay Gould and  Richard Lewontin (beautifully expressed through analogy in The Spandrels of San Marco and the Panglossian Paradigm ) and in the UK by C.H.Waddington. Under these conditions the scepticism of lepidopterists and statisticians were no longer discounted , and various other hypotheses about the rise ( and subsequent rapid fall ) in the melanistic peppered moth population were aired.

Natural selection, which was first considered as though it was a hypothesis that was in need of experimental or observational confirmation, turns out on closer inspection to be  a tautology, a statement of an inevitable although previously unrecognised relation. It states that the fittest individuals in  a population (defined as those who leave the most offspring) will leave the most offspring. Once this statement is made , its truth is apparent…. CH Waddington, 1966


Frustratingly for the eco-geneticists the possibility of organising a sufficiently ‘rigorous’/ controlled experiment ( eliminating alternative explanations and introducing control populations) seems impossible , leading us back once again to the distinction between lab science with its simple cause-effect relationships , and the chaos of linking observation to proof in the real world.


I remember my reactions to the efforts of ecological genetics  as vaguely desperate stuff, and found myself particularly sceptical about traces of purposiveness in the idea of natural selection. I cant decide now whether I was sniffing out tautology , or simply found the determinism anathema to my fledgling Marxism.

Not surprisingly I preferred SJG’s ideas . A writer and polymath, left-liberal, and able to drop his ideas into magazine article length pieces, peppered wth asides about baseball and books, his view of evolution seemed more credible. It finds room for the  then discredited  (but instinctively attractive) ‘jump’ theory of evolution, in the suggestion that populations contain many mutations which are neither harmful or useful until a particular situation makes them so, and that survival of individuals and species have a lot more to do with luck than fitness. Within his accounts I can find room for the jumping universe ,  not-knowing  and randomness. He also will let go an occasional side swipe at the Oxbridge set. Perhaps unsurprisingly his ideas have made much less impact in the UK, and despite all of his intellectual chutzpah, do not offer a clear new paradigm.

In the UK we are still sheltered from the tide of creationism ( and its intellectual wing , intelligent design) that is threatening free thought in the US. But it is coming , as faith schools, Brexit and increasing university privatisation  play out and create a cold climate for liberal thought.  It will become harder to describe your world-view as ‘only a hypotheses that seems to make best sense of things to me’, and easier to look for justification in knowledge systems that others may not understand. To do so  is the challenge for post modernism in the face of all kinds of backward looking certainty.

There is a story near the end of Moths and Men about a biology teacher who is trying to update his teaching about the famous experiment . This involves trying to introduce an understanding about the scale and scope of the experiment , the flaws in the design , the problems in eliminating the flaws, the process of deciding what parts of the story we can still believe , and perhaps the process of being close to the gaining and losing of certainty in knowledge. I d like to think that approach might spread..


* A quick scan over Wikipedia about Moths and Men and the peppered moth experiment will show how live the controversy about the book is. The most recent posts concern the reproduction of the experiment by Michael Majerus, a now deceased senior entomologist of the Ford school, who claims to have corrected the experimental bias and found the same results , which he reiterates conclude that predation causes the differential in survival of the different forms.   His conclusion is supported by one of the American entomologists who questioned the original findings.

However the paper is only available from academic websites which charge substantial sums to non-academic subscribers. This is of course of no concern to scientists who believe journalists , and the general public are unable to understand the subtleties of their work – as the other criticisms of Hooper suggest. And which completely miss the point about why she found a market for her book , and the destabilising claims of creationism are able to take root in the post-consensual heart of a sceptical public.

If I ever get to see the paper I will be interested to see if it has addressed the suggestions for alternative explanations for differential spread of melanistic moths. And I promise to make my findings freely available, which is how we challenge the  conservatism of orthodoxy , whether its theistic or scientific.







One thought on “Cuckoos and Peppered Moths – how natural is selection?

  1. Damn lies & statistics! The epidemiology approach to trying to discover the underlying cause of anything is problematic. Trying to isolate one factor in a real life situation is impossible but there are still well–funded research projects ongoing. The alternative of lab-research is also imperfect because the natural situation has been removed……
    So, scientists all use statistics and have various ‘set’ criteria that they assume are crucial to the event they are studying. Sometimes these conditions may be good – particularly for something quite tightly controlled anyway. For most stuff it’s baloney and probably results are skewed to fit the paradigm (so the graph looks convincing and the discussion is easy to write – the next grant more likely to be funded!


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