An intresting question Carly, however you have made an assumption that I belive is untrue. You ask why allergies evolved, I am not so sure that they did evolve.

One possible cure for allergies is to introduce worms into the gut of the sufferer, these seem to supress allergies.

I would therefore reason that a dependance on parasites of some form has developed. As health of a country improves there is also an increase in the amount of allergy sufferers. By removing the parasites we have removed the regular strain on our immume system the immune system begins to attack anyting that it can such as; pollen, nuts and the self.

So the gene-enviroment interaction was benifical in the past but now that the enviroment part has changed the gene part nolonger provides a benifit. As this has only occured recently on an evolutionary timescale there has not been a change in the genetics to get around this. There is also very little selection pressure agenst allergies, many people that do suffer from them are not unable to pass on their genes.

First, we should talk about allergies from the root cause.

What do allergies mean? They mean that the economy of the human body has some strong immune responces strongly to some kinds of antigenic substances. These kind of immune response may destroy your tissues and lead to some severity of different hazards.

Then, why we sometimes are suffering from the allergy? One important reason is by inheritance which is inevitable. The other reason is that maybe we contact the allergen which means something which can make us allergy. There are some kinds of allergen in our daily life as follows.

The first one, the ingestion of food allergen, incluing eggs, milk, fish and shrimp. The second category, inhalant allergen, contains pollen, animal skins and epiphyte. Last,contactant, such as oil paint and cleaning agent.

So ,i think what we should do maybe is just to avoid to suffer from the allergies.

In my opinion, allergies are not good things. They at least lead us a bit out of sorts.