If you have a cold. From ScienceDaily:
Research suggests that our selfish genes are behind the aches, fever
The symptoms that accompany illness appear to negatively affect one’s chance of survival and reproduction. So why would this phenomenon persist? Symptoms, say the scientists, are not an adaptation that works on the level of the individual. Rather, they suggest, evolution is functioning on the level of the “selfish gene.” Even though the individual organism may not survive the illness, isolating itself from its social environment will reduce the overall rate of infection in the group. “From the point of view of the individual, this behavior may seem overly altruistic,” says Dr. Keren Shakhar, “but from the perspective of the gene, its odds of being passed down are improved.”
In the paper, the scientists go through a list of common symptoms, and each seems to support the hypothesis. Appetite loss, for example, hinders the disease from spreading by communal food or water resources. Fatigue and weakness can lessen the mobility of the infected individual, reducing the radius of possible infection. Along with the symptoms, the sick individual can become depressed and lose interest in social and sexual contact, again limiting opportunities to transmit pathogens. Lapses in personal grooming and changes in body language say: I’m sick! Don’t come near!More.
Of course all this couldn’t just be happening because the person is sick and behaves that way, whether the behavior is “adaptive” or not. Lots of nonadaptive behaviour is harmful but not fatal early on, thus not likely to be bred out. The same way extinctions can just happen, even though we don’t typically think of them as adaptive for the extinguished species. Oh wait! That paper is just down the road… 😉
It’s almost as if they now need to find a retirement job for Dawkins’s selfish gene. At any rate, it’s a sign of a theory in trouble that it purports to explain conundrums that are only conundrums if one believes the theory (as in, why do sick people behave that way when it isn’t apparently adaptive?).
No wonder Karl Popper saw “adaptive” as a tautology. By the way, whatever happened to Die, Selfish Gene, Die?
It’ll be interesting to see is whether, in the age in which the Royal Society is rethinking our current approach to evolution, that sort of cultural artifact of pop evolution will appear again and again, oblivious to changes in basic concepts. If not, when and how will the rockslide start?
See also: Language study PR namedrops Darwin; sure to get taken seriously now
and
Finally, retiring the term “living fossil” is hot?
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Here’s the abstract:
When we contract an infection, we typically feel sick and behave accordingly. Symptoms of sickness behavior (SB) include anorexia, hypersomnia, depression, and reduced social interactions. SB affects species spanning from arthropods to vertebrates, is triggered nonspecifically by viruses, bacteria, and parasites, and is orchestrated by a complex network of cytokines and neuroendocrine pathways; clearly, it has been naturally selected. Nonetheless, SB seems evolutionarily costly: it promotes starvation and predation and reduces reproductive opportunities. How could SB persist? Former explanations focused on individual fitness, invoking improved resistance to pathogens. Could prevention of disease transmission, propagating in populations through kin selection, also contribute to SB? (Public access) – Keren Shakhar, Guy Shakhar. Why Do We Feel Sick When Infected—Can Altruism Play a Role? PLOS Biology, 2015; 13 (10): e1002276 DOI: 10.1371/journal.pbio.1002276