Why natural selection will never cure the common cold!

In my last blog entry, I described a trip to Uppsala, Sweden, and the Beaver Snaps I drank there. I learned at the time that Beaver Snaps are often a northern Swedish speciality. This last week, I returned to Sweden – this time much closer to the land of Beaver Snaps. I was in Umea for their annual KBC days, an event where researchers from several departments at the university gather together to interact and share their research findings. My job was to give a plenary talk of general interest – and I spoke on Humans, Evolution, and the Future of Biodiversity. This was simply a grandiose title for what amounted to an advertisement for the importance of considering evolution when evaluating how human activities will shape future biodiversity. I also gave a research talk about ecological speciation.

The cool thing about trips like this is that you talk to all sorts of crazy people who have all sorts of crazy ideas. These ideas are sometimes useful and inspiring and sometimes not, but they are certainly always interesting. And sometimes these crazy ideas are what I remember most, such as in my “What did I learn today” entry from Belgium last winter. On this most recent trip, I spent some hours arguing about behavioural syndromes with my host Tomas Brodin – I remain to be convinced! And Lennart Persson espoused his paradoxical idea – they even have theory and data! – that increasing mortality on a given age class will increase the number and biomass of individuals in that age class. Already published in Science and PNAS, this theory is coming soon to a bookstore near you.

Now that stuff was bizarre enough but perhaps the most surprising discussion started with a question from someone who had seen my general talk. He wanted to know why natural selection has not eliminated our susceptibility to colds – after all they do make us damn miserable and we seem to get them all the time, particularly those of us with kids (more about this later). Now the usual answer to this question might be that colds are caused by micro-organisms that have very short generation times that allow them to adapt to us better than we can adapt to them. But I figure the more interesting answer is that colds don’t currently reduce our fitness – so selection won’t act to eliminate them. I certainly had a raging cold at the time and so the question stuck with me. I began to wonder if colds had actually reduced my reproductive success. I have two kids now but, without colds, would I have three – or four?

So clearly we need a study on this. Perhaps we should ask people whether or not they conceived their children when they had a cold. I suppose that would be hard to remember (hopefully so anyway) and so maybe we could instead test whether people that get more colds have fewer children. Better yet, we could experimentally induce colds in some bars and not others (that should be easy – we just infiltrate the dish washing staff) and then monitor mating and reproductive rates of the patrons (probably a bit harder). And, to figure out if sexual selection was the reason, we could take a bunch of people with colds, give some decongestants and not others, and send them into bars with instructions to ... well you get it. And why not take this train of thought to its logically absurd conclusion. I noted earlier that people with kids get more colds than do people without. Maybe this is a case of selection through sibling conflict. It clearly benefits the kids you already have if you don’t have more kids – because the available resources are divided to a lesser extent. So maybe, just maybe, colds are adaptive in children because they enable them to infect their parents thus (further) reducing the chance the parents will have more kids. Sick kids really are the birth control we always thought they were!



My first daughter, Aspen, trying hard to make sure I don't have a second daughter. It didn't work - perhaps because she couldn't have a cold all the time.