When the spring season rolls around, many of us find ourselves suffering from allergies to pollen. This could be classified as a seasonal flu, hay fever, or any other form of reaction to those tiny particles that plants release to fertilize their own species. Weeds, grasses, and trees are all known to release some form of pollen grains at a certain time of the year. We may find ourselves sneezing, coping with runny noses, and having to suffer several other uncomfortable symptoms due to the allergy-triggering pollen. This has been going on for several centuries now, so why hasn’t evolution stepped in yet?
When answering this question, consider this: do a stuffy nose, itchy eyes, and trouble sleeping at night affect your ability to go about your daily life? Apart from the discomfort, the answer is usually ‘no’ for most people.
You can still eat, talk, and breathe with a stuffy nose, so primitive man could still eat, communicate about important and unimportant matters, and run and do other physical tasks requiring hard breathing. You can still drive and read with itchy eyes, so the aim of primitive man might not be affected enough to prevent them from killing their food or gathering it. You can still drive with troubled sleep; you can still go about daily tasks even without getting the recommended eight hours of sleep; in the same way, primitive man could still be a functioning member of his or her community, even if they don’t feel like it.
The fact is, if our ancestors couldn’t hunt/survive with these symptoms, none of us would be here. So this did not affect them the way you might think it would. Hay fever and similar conditions don’t usually kill people, so there was no reason why evolution would even be applicable here.
Studies do show that a disturbed sleeping cycle, stress, and other disturbing aspects can potentially shorten our lifespan. However, this effect is not so drastic that it starts taking the lives of people before they reach the age of production. It’s perfectly normal for a person who suffers from pollen allergies to lead a long and mostly healthy life.
Also, evolution goes for “good enough”. Sickle cell disease, for instance, will greatly shorten your lifespan. It would be especially short without treatment in such a case. However, it also protects equatorial populations from malaria (large mosquito populations pass malaria to humans), as those with the disease are immune. Some random genetic mutation kept someone alive long enough to reproduce and pass the gene on to their kids, and their kids lived long enough to reproduce, etc. Those who got malaria were pretty much dead, so a lot of babies and children died along with adults. But people with sickle cell didn’t, so they passed on their genes with enough gusto so that it still exists today.
Even though a primitive man with sickle cell wasn’t going to live as long as other adults in his community who never had that disease or contracted malaria, evolution never selected against it because it worked to pass on the genes. If sickle cell mutates to the point where it kills people before puberty, it will be selected against since there will be too few people to pass it on.
These primitive people with allergies? Whatever the effects of those allergies, they stayed alive long enough to have kids, who stayed alive long enough to have more kids, etc.
This discussion about sickle cell disease can help us understand the reason we are not immune to pollen. In a sense, the pollen allergy gene doesn’t affect the ability or opportunity for human beings to pass on their genes. Hence, while we may not feel our best when suffering under these allergies, it’s not like they affect our lives in a major way. They don’t affect fertility, threaten the lives of young people, or make us so weak and disabled that we can’t fend for ourselves. This is why pollen allergies remain a part of the human gene pool and will probably do so for ages to come.