The expression “man-flu” has entered the Collins English Dictionary, according to the BBC Radio 4 Today Programme this morning. This seems a good cue to unveil my theory of man-flu, mentioned a few weeks ago.

As you may recall, the theory has received the full support of male evolutionary biologists in exchange for a round of beers. It gets a much more mixed reception from women (particularly academics), admittedly with no alcohol as an inducement, so not an accurate control.

But I think there is a serious evolutionary biological purpose to man-flu, or the exaggerated symptoms that the pair-bonded, male homo urbanis feels when infected by virus. It was designed to make him stay home from the hunt.

When I started attending the Bath University Sports Training Village for physio treatment, I noticed signs everywhere urging athletes to stay away if they had a virus. You would not see that in an office. While the purpose here is primarily competitive, elite athletes are arguably the closest we have to the hunters of our past. Viral infection is devastating to performance in lost training time and risk to health.

Hunters living in small communities probably encountered viral infections less often than we do from our globalised, commuting lifestyles. Moreover, their “work” regimes would routinely raise body temperature and burn off most viruses before they took hold, in the way a fever is also designed to. So it might be fair to assume that a virus was a rare event, and one to be wary of.

To see what hunting would have required of paleo man, take a look at the video below which we’ve linked to before. An eight-hour run, chasing down an animal to exhaustion, is a form of marathon few of us have to even think about except on a voluntary basis. But it naturally produces a dangerous form of exhaustion in the hunter himself. Paleo man needed to be highly sensitive to his physiological condition before setting out on such a trek. He would check his fitness. He would know the action of his heart intimitately for advanced warning of illness. And I speculate, therefore, that there is some value in the hunter-gatherer male body over-reacting to the presence of virus.

There were at least two major threats. First, exhaustion leading to collapse from the infection reaching his heart – myocarditis – which can be fatal: it is the reason why athletes (amateur and professional alike) are advised not to run marathons within a month of normal viral infection. Second, sabre-tooth tigers: he’d need to out-run them.

So a virus that today induces malingering in the male computer operator was designed to encourage paleo man to stay home around the camp fire. Any other action significantly increased the risk of death.

All that is needed to invalidate this theory is proof that women went hunting too. Any offers?

Watch again an amazing hunting day in the life of the Kalahari bushmen:-

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