I love peanut butter.
Put it on waffles, bananas, apples...hell, I'll even eat celery.
To my dismay, we are now living in a world where kids can’t bring a peanut butter and jelly sandwich to school. Restaurants have to take up space on their menus to indicate whether peanuts have nuzzled up next to any other foods. If we for one brief moment anthropomorphized that jar of Jif, I’d feel deeply sympathetic to this poor little jar and the feelings of loneliness and isolation it must be experiencing. But the real issue to confront is whether we are allowing our own species’ weaknesses to multiply by accommodating the plethora of food-related allergies present in populations around the globe. If natural selection were allowed to proceed without our intervention, what would be revealed?
Is the human race destined to fall to the feet of the dashing Mr. Peanut?
(And what are allergies anyway?)
Not all allergies are created equal. That is, not all allergic reactions are a result of the same series of steps. And don’t worry; I’m not going to attempt to describe all possibilities for you here because food allergens, not the complex modes of allergic response by our bodies, are the topic of this story. In general, the ailments of allergies are a result of an over-reaction of our immune system. Our adaptive immune system is essential to defending our bodies from all kinds of pathogens like harmful proteins that are sneaky enough to get around our innate immune defenses (think mucus, tears, and cells within the body that can engulf foreign particles and break them down like the blob). The power of the adaptive immune response comes from its specificity and development of immunological memory. Plasma cells (also known as B cells) make a ton of antibodies that are able to target specific invading molecules. Once triggered, these cells circulate in our blood vigilantly prepared for a prompt attack against the same thing in the future! Sometimes however, certain cells misinterpret something harmless as harmful. This is an immune hypersensitivity; our bodies over-react.
There are different types of food hypersensitivities, but the most common in relation to allergy is “type I”. These are immediate reactions that result from the presence of a particular type of antibody, named IgE. IgE antibodies can be produced to match all sorts of proteins. A person experiences annoying allergy symptoms because their body becomes “sensitized” to harmless antigen (for example, a peanut-related protein) by producing IgE antibodies that pair with it. When these molecules match up, they signal to our bodies to trigger responses (sneezing, tearing eyes, a seemingly never-ending supply of mucus, etc.) ultimately to expel whatever it is that shouldn’t be inside of us. What a buzzkill, right?
Why do allergies exist? There’s more to it than sniffles.
They may seem like nothing but a waste of energy now, but IgE type antibodies evolved as an adaptation to protect against dangers that were prevalent in the less industrialized culture of early humans. Parasitic organisms were at one time much more of a daily concern for early humans. Strutting around, no shoes, no city or suburban sidewalks…nothing but the ground beneath their torn up feet and more of an overall general concern for creepy crawly tapeworms sneaking in their scrapes. IgE antibodies were very effective at responding and initiating an immune response against these parasites, and over time individuals that possessed the genetics that provided this protection survived more often than those that lacked it. The frequency of this trait increased in the population due to the success of these IgE-producing humans. So why, you may ask, are IgE antibodies still prevalent in our genetic code if we don’t have a high risk of contracting parasites regularly?
It comes down to the vast complexities of natural selection!
Allergies have both a genetic and environmental foundation. The idea is that a person’s genetics predispose them to being likely to develop an allergy such as that toward food proteins, and environmental exposure may allow such a reaction to develop. Scientists are presently working on identifying specific genes and gene regions that may lead to susceptibility to certain allergies (such as CD14), but a lot is still unknown. However strong familial tendencies for allergic disease are present, indicating some level of heritability for genes involved in allergy symptoms or susceptibility. There has even been a scientific study examining the genetics of peanut allergy in a set of twins, supporting a 70% genetic contribution toward food allergy! Because of this, genes related to allergy should be under pressure as either positive or negative selection, right? And since food allergies are nothing but a sign of a weak genetic makeup, they would slowly fizzle out of the population if natural selection were allowed to proceed, right? We all know that catch phrase, “survival of the fittest”…Ah, yes. There’s that dark humor!
Well nothing beyond my peanut butter cravings actually, but sex has everything to do with it.
So are we weakening the gene pool by accommodating people with a collection of food hypersensitivities? Maybe it seems like a valid claim. But here’s the clincher: fitness in terms of natural selection doesn’t mean living to tell the tale of the time a peanut grazed your left arm. All that matters is if an individual has good reproductive health and ultimately produces offspring that will carry on some of his/her DNA. Perhaps this means that if we take a moment to step back a bit and consider humans as the animals we are, shifting our focus from medicine and epidemiology, we may see that being allergic to the peanut does not decrease our reproductive fitness. I think we can all agree that a grocery list of immune hypersensitivities is not advantageous, but at this point in time is it really a disadvantage? I’d say no. Things aren’t quite that nuts…yet.
All jokes aside, the curious thing is the recent increase in frequency of food allergies, especially that of the salty and delicious peanut. The Center for Disease Control reported a general food allergy increase of 18% between 1997 and 2007 and interestingly, prevalence of food allergy was greater in higher income level brackets. In the past decade, the frequency of food allergies in children has more than doubled. Many evolutionary biologists and immunologists support a “hygiene hypothesis” linking food allergy to modern day cleanliness and shift in diet; a concept originally proposed in 1989. We’ve got cleaner water, rubber-soled kicks, and hand sanitizer dispensers every twenty feet. While decreasing our exposure to pathogens and microbes sounds like a good thing, this hyper-clean environment may actually cause our adaptive immune response to atrophy and over-react more. Evidence suggests that sufficient exposure to certain infection agents and microbes early in life is important to priming our immune systems to respond appropriately.
The highly processed nature of our food may also be involved. Our foods are often processed before we consume them, meaning that the proteins present in those foods may be modified in a variety of ways depending on the preparation. High temperatures of peanut-roasting (180 degrees C) may alter protein shapes and has been reported to increase allergen effects. Additionally, it's been seen that 70-80% of children allergic to milk or eggs can actually tolerate cooked or baked forms of the normally allergenic food proteins, supporting the idea that different conformations (shapes) of food proteins may interact differently or not at all with IgE antibodies in the body. Read more here.
Is it too late?
While peanut allergy doesn’t presently affect reproductive fitness, this sensitivity is increasing among younger and younger age groups. The risk of a very serious allergic reaction in children puts their life at risk during a stage prior to reproductive maturity. Over time, and as we may already be observing, it is possible that genes associated with severe peanut allergy may be passed on continually through generations through strict avoidance of peanut contact and more and more children born with immune hypersensitivity. On top of this, studies show that kids with food allergies also experience impaired growth during development. Where does it end?
A 2013 article in the New York Times covered a really cool story of a physician interested in trying to help children overcome severe food allergy. Dr. Nadeau presents some stories of success using gradual oral immunotherapy. Sounds fancy, but the concept is simple. By exposing a person to incremental amounts of a specific allergen (starting with very little of course), the immune system should slowly become desensitized to that protein and stop interpreting it as harmful. She isn't the only one who is having success with this technique and data released from the Lancet (just about a month ago!) from a phase II clinical trial for peanut-protein immunotherapy reported that 62% of allergic individuals were desensitized after 26 weeks of incrementally increased consumption. Check out this brief news story on the New England Food Allergy Treatment Center! On the weirder side, the importance of evolutionary biology in medicine has been emphasized by the suggested use of infection with those same types of parasites I mentioned earlier to actually alleviate allergy symptoms! It's worth reading into if you're as intrigued and mildly grossed out as I was.