Question 041121b: Is the change in color of the peppered moth (biston
betularia) from light grey to black an example of "evolution under your
own eyes"?
see also http://www.iconsofevolution.com/embedJonsArticles.php3?id=590
(in English)
see also http://www.arn.org/docs/wells/jw_pepmoth.htm
(in English, with pictures of the moths)
see also http://www.weloennig.de/BistonA.html
(mostly inGerman. Auf deutsch)
Answer 041121b: No it is not.
Is was found that a black version of the peppered moth is prevalent in
areas where birch trees were darkened because of industrial polution. once
the polution decreased and the birch trees became white again, more moths
were white, too.
Huxley wrote in 1958 that this is an example for "evolution
under your own eyes". The change form white to black and back to white occured
within 100 years. Huxley's explanation was that sudden mutation caused a
few of the moths to become black. Thus they were not as easy to be found
and eaten by birds than the white ones, who were clearly visible on the blackened
tree trunks. Thus mutation led to selection and to a new species - a prime
example fro evolution!!
....actually not. Here are the counter arguments:
1. The black varieties of the peppered moth (and other moths) occur everywhere,
if the trees are blackened by polution, or if the trees grow in unpoluted
areas. Black and white ones coexist.
Citation: (Lees and Creed 1973):...melanic forms of several species which
today show industrial melanism also occur in unpolluted areas and have done
so since before 1870.
Citation: (Parkin, 1975):It seems the melanism in moths can occur almost
anywhere....some species have melanic forms that live on peat bogs, in dark
shady pine forests, or even, perhaps, in areas where the trees are blackened
by frequent burning....Such polymorphisms have probably been in existence
for a very long time, and it would be of interest to know whether any of
these alleles have migrated into industrial areas.
Interestingly, it can be found that the black variation is more prevalent
in clean areas than in poluted areas.
Citation (West about the american Biston betularia cognataria 1977):The
melanic [black] swettaria form of B. b. cognataria is at a low frequency
in two localities in the central Appalachians of southwest Virginia (1.2
+- 0.2 per cent at Blacksburg and 2.9 +- 0.4 per cent at Montana Lake)....why
is the frequency higher in the seemingly unspoiled montane forest at Mountain
Lake than in the vicinity of a minor pollution source like Blacksburg? There
may be gene flow from areas of higher swettaria frequency or there may be
subtle effects of air pollution at MLBS and less so in Blacksburg that have
increased the relative fitness of swettaria in some way not primarily
related to lichen cover and the colour of tree limps and trunks.
2. In order to change from white to black no formation of new genes is
necessary. It seems that all moths have thew gene to produce black pigment.
Just in most of the moths this gene is switched off. Now, from time to time,
in a few moths, this gene is switched on and the moth becomes black. Thus
the black moth did not evolve from the white ones. They coexist.
3. The propsed selection of the new "evolved" black form comes from the
better visibility of the white form on the black tree trunks. But the peppered
moth does not rest on tree trunks . It also does not rest during the day.
Rather, it rests during the night and under leaves! So there is no evidence
that the change of tree trunk color is responsible for the increase of the
black variant.
Some authors even went so far and glued DEAD moths onto tree trunks and
photographed them as evidence for the proposed selection mechanism!
see pictures of this at http://www.weloennig.de/pic/BisonGr.jpeg.
If you are not convinced that this is a fake picture, ask yourself how high
is the propability to see two moths, one white and the other one dark at the
same time on the same tree trunk?
4. do birds see the same colors and contrast as humans? I doubt that.
It might well be that the visin of birds and humans is different, so that
what is an obvious difference in contrast is not necessarily so for birds.
As a conclusion, we can say:
"Looking at the famous case of industrial melanism more than 20 years
later, we have to point to the most surprising fact that the case has recently
been found wanting (Sargent et al.; 1998; Majerus, 1998; Coyne, 1998). ...
Here is the new evidence: After summarizing Kettlewell's presentation of
the Biston betularia instance, Coyne (1998) states the main points of the
critical recent observations as follows:
(1) The peppered moth normally doesn't rest on tree trunks (where Kettlewell
had directly placed them for documentation).[some other authors even glued
dead moths onto tree trunks to observe the eating by birds.]
(2) The moths usually choose their resting places during the night, not
during the day (the latter being implied in the usual evolutionary textbook
illustrations).
(3) The return of the variegated form of the peppered moth occurred independently
of the lichens 'that supposedly played such an important role' (Coyne).
(4) Kettlewell's behavioral experiments have not been replicated in later
investigations. Additionally, there are important points to be added from
the original papers, as (5) differences of vision between man and birds
and
(6) the pollution-independent decrease of melanic morphs (for details,
see the authors referred to above)."
This citation is adapted from Prof. Loennig's internetsite about evolution).
back to Main page