Kettlewell and the Peppered Moths

  1. I'm just wondering how many of you learned the Kettlewell experiments and how it proved solid evidence for evolution in high school?

    I later learned that the Kettlewell experiment was riddled with many problems (using dead moths, assuming birds have similar human vision, contradictory data in other parts of the country collected by Kettlewell and other scientists, as well as the fact that the moths don't rest vertically on the tree trunks but rather below the branches upside down).

    Why is this poor experiment commonly cited as evidence for evolution in High Schools especially with the threat of creationist belief on the rise.
  2. jcsd
  3. Evo

    Staff: Mentor

    You seem to have been duped by creationist/ID propaganda. The Kettlewell experiment is still considered a fine example. It is the creationist/ID camp that has spread misinformation about it.
  4. no serious experimenter suggested that Kettlewell’s results were invalid. Indeed, subsequent experiments to test these criticisms broadly confirmed Kettlewell’s results

    I partially disagree with this statement; Kettlewell's results incorrectly demonstrates natural selection and his conclusion on melanic industrialism was little too simple and did not completely explain geographic distribution of carbonaria or typica.

    it is our view that past attempts to assess the relative fitnesses of the forms, using formal predation experiments, have been flawed for two reasons. First, moths have been placed out on the wrong parts of trees (e.g. Howlett & Majerus, 1987; Majerus, 1989). Second, moths have been placed out in positions appropriate to their phenotype on the basis of human perception, without consideration of the UV element of the moths' pattern, or that of the substrates. The same criticism may be made of assessments of the relative crypsis of the forms of the peppered moth in different regions when these have been made by humans, with moths placed on tree trunks. The inclusion of these flawed assessments in multiple regression analyses (e.g. Lees et al., 1973; Bishop et al., 1975; Steward, 1977a,b) will lead to misleading deductions of the importance of crypsis
    -A bird's eye view of the peppered moth

    Michael Majerus himself says in his book Melanism: Evolution in Action, "in most predation experiments peppered moths have been positioned on vertical tree trunks, despite the fact that they rarely chose such surfaces to rest upon in the wild" (p. 116)

    The understanding of industrial melanism in the peppered moth (Biston betularia) (Lepidoptera: Geometridae)
    Rory J. Howlett, Michael E. N. Majerus
    Computer models based on these selective coefficients show that they are not sufficient accurately to explain observed melanic frequencies

    I think a less contested example of natural selection would be a far greater way to provide evidence for school children. If the Kettlewell experiment was presented in such a manner that students could think critically about the experiment (specifically its method) rather than accepting it as "white moths are eaten on black trees because they're visible" then it would be a worthwhile experiment to talk about in class.
  5. Evo

    Staff: Mentor

    You can read the controversy over the excerpts you posted here.

  6. Evo

    Staff: Mentor

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