MadSci Network: Evolution

Re: Do Lamarcks theories provide a good explanation for the change in the moth?

Date: Fri Aug 19 22:22:32 2005
Posted By: Michael S. Robeson II, PhD Student in the Ecology and Evolutionary Biology Dept.
Area of science: Evolution
ID: 1122513656.Ev

No, Lamark's ideas do not provide a very good explanation for moths. His ideas 
for acquired characteristics would most likely mean that all the moths would 
eventually become light or dark colored. In contrast, according to Darwin's 
theory of Natural Selection and basic population genetics, there will tend to 
be (recessive) alleles that are expressed in the minority.

It is the access to this minority population (of recessive alleles) that allows 
the species to alternate between light and dark color patterns when the 
environment changes. This is because studies show that these color patterns can 
appear as dominant or recessive alleles. Meaning that although a moth may be of 
one color type, it has the ability to carry and pass on the recessive color 
(diploid organism: they have two copies of each gene), which can express itself 
when mating with another heterozygote or homozygous recessive moth. So, you 
would have the possibility of having offspring that can express or also carry 
the recessive (or mal-adaptive) trait. 

So, mal-adapted organisms are maintained in small numbers for a long time 
before that allele becomes wiped from the population.

The appearence of mal-adaptive moths would not occur under Lamarkian thinking. 
This is because Lamarkian thinking states that all individuals under the same 
environmental pressure would pass on the same acquired, beneficial traits to 
their offspring. Obviously, we do not see this occur in nature.


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