Allergies and the Evolutionary Process

Name: Ray
Status: teacher
Grade: 9-12
Location: Il

Question: What would be the evolutionary purpose for allergies?  It seems 
they are nothing but a weakness and if evolution is to allow better traits to 
dominate then the allergies must be a strengthened, the same as with colds and 
other problems.
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First, the frequency of individuals having a negative trait is 
often maintained in the population (this relates to population genetics).  If 
the condition is only slightly harmful those frequencies may even increase.  
Also, there is or was a silver lining behind many negative traits (sickle cell 
anemia, cystic fibrosis, etc).  Many had some advantage which kept the gene 
frequencies up despite their obvious drawbacks.  Lastly, it is the interaction 
or total impact of all the genes in an individual that determines fitness.  
Genes for mildly negative traits may tag along with little negative selection 
pressure.  It is only the severe autoimmune disease or immunodeficiency 
disorders that will prove lethal and have little opportunity for being kept.  
Allergies are quite mild by comparison.  How allergies develop in an 
individual is still a very important part of this puzzle.  If man-made 
compounds in any way enhance this process, it would further explain any 
increases in their frequency.  Of course medication helps us cope and minimize 
the negative effects as well.

Lou Harnisch
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This is sort of off the top of my head, but the basic idea is 
here:  as Lou Harnisch wrote, selection happens at the level of the 
individual, not that of the gene (or in this case, or phenotype.  It seems 
that evolution has often put up with useless and what we perceive as useless 
or negative features for other purposes.  It is certainly the case that 
survival of organisms that immune function is required for our survival, and 
that of many other species.  After all, we provide a rich food and source and 
a controlled environment for all sorts of parasites.  So the advantage ge of 
having and immune system is huge.  In contrast, the cost of most allergies 
seems to be rather small - Lord knows I get nasty hayfever, but I hope that it 
will not ruin my chances of survival or reproductive success.  The important 
thing to note here is that it is *not* just because a feature has evolved does 
not necessarily mean it has a purpose.  This is fundamental to evolutionary 
theory.  What for instance, is the purpose of male nipples?  For the answer to 
this and for an excellent series of articles on evolutionary biology, I would 
like to recommend d any of the books by Stephen Jay Gould.  You will probably 
find some in your local library.  They are readable, accurate, and amusing.

Ethan Benatan
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