When I was studying Biology at ‘A’ Level, the Peppered Moth was advanced as the classic evidence for Darwinian evolution. Admittedly, Haeckel’s imaginary ‘ontological recapitulation’ drawings were also flourished at us as authoritative proofs, so perhaps I should have been less credulous about the moths. But then, I was in my teenage years, and clamping firmly onto the Darwinian bait was what everyone did.
Most children who studied Biology at secondary school no doubt have prominent memories of moths, and finches and strangely-shaped glass vessels, containing exotic gases, out of which novel forms of life emerge spontaneously – because it just does. The Peppered Moth was a great favourite because it supposedly proved how light-coloured insects evolved into darker-coloured forms in order to survive predation during the industrial revolution.
At University, still studying Biology, the moths figured prominently – as they did in the main secondary school textbooks when I was training as a science-teacher later on. Like Monty Python’s famous cafe, where you could have everything you wanted provided it included Spam, those darn Peppered Moths were always on the menu.
Apparently, they still are. Wikipedia features the little darlings prominently, as perhaps one might expect. The same story is regurgitated on the Butterfly Conservation website, and BBC Bitesize pulls off the same trick. There would be little point in listing all the instances of this childhood fairytale that exist on the interweb – Google generates 895,000 of them, the internet equivalent of the repetition of myth.
Of course, the whole Peppered Moth saga is, in fact, no persuasive evidence of Darwinian evolution at all. If the science is at all to be believed, there were more dark-coloured insects around at the time of the industrial revolution (when those trees got sooty), and rather less of them after the Clean Air Act. Evolution is supposedly a process whereby ‘natural selection’ leads to permanent adaptive changes in populations of organisms, fuelled by a continual background instance of genetic mutations. There has been no such change here, and yet the Peppered Moth is still heralded, on a multiplicity of websites as “one of the best known examples of evolution by natural selection, Darwin’s great discovery, and is often referred to as ‘Darwin’s moth’” (according to Butterfly Conservation).
However, I did, quite intentionally italicise the use of the word ‘if’ in the above paragraph when referring to our belief in the science itself, for even that is highly questionable. Those grand claims are based upon some work conducted by the physician, Bernard Kettlewell in the 1950s who boarded the Darwinian juggernaut and made his place in history by discovering what he called ‘Darwin’s missing evidence’. This was a big help to those promoting the evolutionary story as it was, frankly, not furnished with the most persuasive stock of supporting evidence. In fact, Kettlewell’s research turns out to be deeply flawed (we knew this apparently in the 1980s, but they certainly weren’t telling school-children!). Peppered Moths don’t normally rest on tree trunks during the day when they could be predated – they hide away under branches and fly by night. This seems an altogether more sensible solution than the painstaking evolutionary equivalent of mutating over the millennia, only to find that some Government had invalidated all that undirected genetic change, by passing the Clear Air Act. By releasing moths onto tree trunks during daylight, Kettlewell had created a scenario that simply did not exist in the wild – and, to add insult to injury, in order to take those famous photos (you know, the ones in all the textbooks), he actually glued moths to tree bark, so they couldn’t hide away. Never has a small insect been so misused and misrepresented. It is a surprise that the Peppered Moth has not developed a complex as a result, so perhaps the brief lifespan may be an aid to its psychological equilibrium.
You couldn’t make it up, but evolutionary polemicists did. Who wants the data to get in the way of a good story, eh?
Which reminds me of Richard Dawkins’ famous aphorism from his 2006 blockbuster, The God Delusion. Here we go, this is Dawkins at his vintage best:
By contrast, what I, as a scientist, believe (for example, evolution) I believe not because of reading a holy book but because I have studied the evidence…When a science book is wrong, somebody eventually discovers the mistake and it is corrected in subsequent books. That conspicuously doesn’t happen with holy books.
This is simply not true. At best, it’s a misleading comment. At worst, it represents the deliberate promulgation of dogma that achieve a kind of pampered, protected species status in the world of ideas. And, yes, they’re still teaching this nonsense to our kids.
I am grateful to a friend for pointing out that there has been a subsequent attempt to validate Kettlewell’s research, as the evident flaws to it had been a source of great consternation to ideological evolutionists such as Jerry Coyne (Not black and white, Nature 396 (1998)). Most of the sources footnoted on the Wikipedia article are (typically) inauspicious, but one did stand out as a valid, counterbalancing contribution.
Between 2001 and 2006, Michael Majerus studied Peppered Moths within a large, unpolluted rural garden in the Cambridge area, attempting to compensate for the perceived deficiencies in the earlier research. Whilst, unfortunately, his premature death interrupted the flow of his research, he had already admitted that his “results may be somewhat biased towards lower parts of the tree, due to sampling technique“. It is no surprise, therefore that his sample of 135 moths shows a greater exposure to other parts of the trees, than those identified by previous researchers, who had, quite rightly, called into question the kinds of conclusions drawn by Kettlewell. I managed to track down his analysis and this indicates that 35% of those moths observed were located on tree trunks (where they are more liable to predation) and 65% of those observed, on branches and twigs (where the dangers of predation are less). Clearly, the actual parameters for Kettlewell’s research could no longer be replicated, due to changes in air quality, and (as Majerus observes) numbers of the darker moths (carbonara) are in decline anyway. As a result there is no statistically significant difference in the daytime predation on darker or lighter variants of the Peppered Moth, and the data indicates that at nighttime, the bats are partial to both variants equally.
Whilst respecting the sheer care and attention to detail of Majerus’ work, the more one reads, the more one is impressed that this is a ‘much ado about nothing’ exercise. Before the industrial revolution, both variants of the moth existed. After the Clean Air Act, both of them still exist, side by side. One has not ‘adapted’ or ‘evolved’ into the other, which is the kind of inference in the textbooks, and was certainly the claim made by Kettlewell. The best one can say is that survival rates of either variant will differ, depending upon natural conditions, which is a bit like saying that the snow will last for longer if the temperature remains below freezing. Coyne’s own comments, criticising Judith Hooper’s book Of Moths and Men, quoted by Majerus, frame the problem: “By peddling innuendo and failing to distinguish clearly the undeniable fact of selection from the contested agent of selection…” (original emphasis preserved). Simply categorising variations in moth survival as ‘selection’ and leaving agency on the shelf, gets us no closer to a proof of Darwinism. Majerus’ work is more evocative of a cherished icon being lovingly polished, than a failed hypothesis being convincingly rescued.
Perhaps as importantly, whilst Kettlewell’s observations provide insubstantial insights into a hypothetical process which purports to hinge on the interaction between genetic mutations and natural selection, they have largely been invalidated by Sermonti & Castatini (mid 1980s), Mikkola (1984) and Jablonski (2012). The latter appears to have caused Coyne considerable anguish, and this backdrop helps to emphasise the sheer paucity of any direct evidence for Darwinism. Every time this happens, the ensuing consternation attains the status of a kind of crisis of faith.
The stakes are high: when Majerus presented his own results in 2007, he reemphasised again the need to teach the story of the Peppered Moth because “it provides after all: The Proof of Evolution” (his own emphasis). Needless to say, that message was swiftly seized upon by those who are wholly invested in the polemic.