Arthur S. Lodge     |     home
Natural selection: the only mechanism?
In a review of Judith Hooper's book, Bruce Grant (2002) writes: "We have amassed enormous records of changes in allele frequency in peppered moth populations that cannot be explained in the absence of natural selection".

In the paragraph containing this remarkable claim, there is no reference to the literature. At the end of the article are two (and only two) references, namely Cook (2000) and  Grant and Wiseman (2002). These references repeat the claim but do not substantiate it.

It is well known, however, that another possible type of explanation, namely phenotypic induction (or phenotypic plasticity,  Spetner, p. 199), should also be considered as a possible alternative to selection. This is an old proposal that has recently been reviewed by Sargent, Millar, and Lambert (1998). Judith Hooper (p. 287) refers to the controversy surrounding this proposal:

 "However, countless breeding experiments with peppered moths have produced the expected Mendelian ratios in the offspring. Thus, the melanic trait is demonstrably genetic, and if it is genetic, how can it be induced? Laurence Cook flatly rejects the induction theory. 'It's absurd'.

Sargent argues that an induced trait may seem to be inherited in a Mendelian fashion if what is actually inherited is a sensitivity to the inducing agent. He conceives of an allele that is turned on or off - expressed or inhibited - in the presence of a particular environmental pressure. 'This idea is not crazy', avers John A. Endler..'."

Endler (1986) writes:

1.  "Natural selection is not easy to detect".  (p.97)

2.  "It is also important to understand the nature and form of any genotype-environment interaction".
      "It is important to use traits that are either independent of environmental effects or have known heritability, so that environmental effects can be statistically removed during the analysis". (p.57)

3.  "A correlation* may suggest a causal relationship, but this is not sufficient to demonstrate it. Unfortunately, it is all too common for only correlation evidence to be presented in the literature; this is very weak evidence for natural selection". (p.58)

* Correlation here refers to correlation in the sentence "geographically varying natural selection will result in a correlation between the selected traits and the selective environmental factors, after the effects of genotype-environment interaction have been removed". (p.56)

See also the discussion in The Devil in Neo-Darwinian Theory Details.


L. M. Cook (2000) Biol. J. Linn. Soc. 69, 431.
J. A. Endler (1986) Natural Selection in the Wild (Princeton University Press)
B. S. Grant and L. L. Wiseman (2002) J. Hered. 93, 86.
B. S. Grant (2002) Science 297, 240.
T. D. Sargent, C. D. Millar, and D. M. Lambert (1998) Evolutionary Biology 30, 299.
L. Spetner (1997, 1998) Not by Chance: Shattering the Modern Theory of Evolution (Judaica Press, Brooklyn, NY).