Expert: Dana Krempels, Ph.D. - 9/19/2010

Question
We humans suffer from differnt kinds of allergies.  And since we take care of our sick siblings, we assure that allergy genes are transmitted.  We would expect that in nature, allergy would be selected away, unless there would be a reason why being allergic would be an evolutionary advantage.  In farmed animals, one would expect that allergic animals were less likely to be kept for further breeding.  Pets would be an exception.  Though I hear about horses with grass allergies and so.  So what would be the occurence of allergies in the animal kingdom in reality ?  
Any ideas of sources of information on that subject ?  

Answer
Dear Ronny,

An allergy is simply the immune system's response to a particular substance to which an individual has become sensitized.  To completely remove the likelihood of an allergy ever developing, one would have to do away with the immune system itself, which would not likely be adaptive for animals as complex as vertebrates.

Sometimes a trait/system that has evolved in response to natural selection can become a liability if the environment changes.  A moth's reflex to follow a bright light, a navigation response using the moon as a cue, has also made them susceptible to flying into artificial flames, bug traps, and inside a lighted house where they will likely pull themselves out of the gene pool.  But the benefit of being attracted to the light may outweigh the loss of a few individuals.

I suppose it may also be that way with allergies.  I don't know if wild animals develop allergies.  If they do, I wouldn't be surprised if they were triggered by anthropogenic substances in their environment.  And if an allergic response was serious enough, those few individuals who developed them would also be out of the gene pool.  But the benefits of an immune system likely outweigh the costs and possible "haywiring" of a few individuals.

When it comes to our own species, and the ones we have artificially selected to serve as domestic "partners," we've changed the game entirely.  Allergies are survivable, and while they may be an economic liability, they are not so maladaptive--at least in most cases--that they remove someone from the gene pool.  So the genetic basis for the allergies remains, people (and pets and livestock) get treated, and our species goes on with our allergies.

I don't have any sources about this, but if you are looking for scholarly articles in this area, you might try:

www.googlescholar.com

But I don't know if this issue has been addressed, or even identified in wild animals.  (It would be pretty hard to study!)

Hope this helps.

Dana