Source: Seattle Times.
According to a new study, it is your and my Neanderthal genes that makes us hate spring pollens that give us our allergies to pollens and animal fur. But hey, feel special, yeah? It's about only 2% of our whole genome that has Neanderthal genes and only 50% of the whole wide human race have it. It may be that it had an advantage against bacterial infection but crossing of genes between our ancestral humans and the Neanderthals also gave us a heightened sensitivity that results in our allergies.
This is prevalent in human populations in Asia and Europe when humans migrated into these areas populated by the now extinct Neanderthals.
More on this in the link above but it is a recommended read. Good science. On top of that, the article explains the reason for these innate immunization responses from the Neanderthals that have served our ancestors so well as they moved into new regions of tens of thousands of years ago.