Peppered moth evolution
Industrial melanism in the peppered moth was an early test of Charles Darwin's natural selection in action, and it remains a classic example in the teaching of evolution.
After field collection in 1848 from Manchester, an industrial city in England, the frequency of the variety was found to have increased drastically.
The story, supported by Kettlewell's experiment, became the canonical example of Darwinian evolution and evidence for natural selection used in standard textbooks.
[8][9][10] However, failure to replicate the experiment and Theodore David Sargent's criticism of Kettlewell's methods in the late 1960s led to general skepticism.
When Judith Hooper's Of Moths and Men was published in 2002, Kettlewell's story was more sternly attacked, and accused of fraud.
His seven-year experiment beginning in 2001, the most elaborate of its kind in population biology, the results of which were published posthumously in 2012, vindicated Kettlewell's work in great detail.
[16] During the early decades of the Industrial Revolution in England, the countryside between London and Manchester became blanketed with soot from the new coal-burning factories.
This led to an increase in bird predation for light-coloured moths, as they no longer blended in as well in their polluted ecosystem: indeed, their bodies now dramatically contrasted with the colour of the bark.
[3] The implication that industrial melanism could be evidence supporting Charles Darwin's theory of natural selection was noticed during his lifetime.
Steward compiled data for the first recordings of the peppered moth by locality, and deduced that the carbonaria morph was the result of a single mutation that subsequently spread.
Even taking into consideration possible errors in the model, this reasonably excluded the stochastic process of genetic drift, because the changes were too fast.
The insert, labelled carb-TE, is a class II transposable element that has an approximately 9-kb non-repetitive sequence tandemly repeated two and one third times.
[31] In 1925, K. Hasebroek made an early attempt to prove this hypothesis, exposing pupae to pollutant gases, namely hydrogen sulfide (H2S), ammonia (NH3), and "pyredin".
[32] In 1926 and 1928, Heslop-Harrison suggested that the increase of melanic moths in industrialised regions was due to "mutation pressure", not to selection by predators which he regarded as negligible.
Salts of lead and manganese were present in the airborne pollutant particles, and he suggested that these caused the mutation of genes for melanin production but of no others.
In 1953, Kettlewell started a preliminary experiment in which moths were released into a large (18m × 6m) aviary, where they were fed on by great tits (Parus major).
[2][36] Theodore David Sargent[a] performed experiments between 1965 and 1969, from which he concluded that it was not possible to reproduce Kettlewell's results, and said that birds showed no preference for moths on either black or white tree trunks.
[38][39] He suggested that Kettlewell had trained the birds to pick moths on tree trunks to obtain the desired results.
[23] Reviewing the book, Jerry Coyne noted these points, and concluded that "for the time being we must discard Biston as a well-understood example of natural selection in action, although it is clearly a case of evolution.
She said that E. B. Ford was a "Darwinian zealot",[43] and claimed that he exploited the scientifically naive Kettlewell to obtain the desired experimental results.
"[49] The intelligent design advocate Jonathan Wells wrote an essay on the subject, a shortened version of which appeared in the 24 May 1999 issue of The Scientist, claiming that "The fact that peppered moths do not normally rest on tree trunks invalidates Kettlewell's experiments".
[50] Wells further wrote in his 2000 book Icons of Evolution that "What the textbooks don't explain, however, is that biologists have known since the 1980s that the classical story has some serious flaws.
"[51] However, peppered moths do rest on tree trunks on occasion, and Nick Matzke states that there is little difference between the 'staged' photos and 'unstaged' ones.
Their concluding remark runs: "These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.
