13 June 2014

The survival of the fittest?

My wife recently got a glamourous pedometer that talks to her smart phone. Not only does it tell you how many steps she has made in a day, what distance she has done and when she has had high activity periods, it also allows her to keep track of what several other teachers from her school have been doing. It turns a reasonably harmless device into an excuse for fiercely competitive exercise as they try to outdo one another with the highest number of daily steps. The recommendation is 10000 steps per day and when that magical number is attained (usually by walking around our bedroom late at night to get the last couple of hundred steps done) little lights flash to celebrate. It's a neat idea to encourage people to do a bit more every day, especially since your mates can taunt you if you are having a good sit down. And the pressure is on every day in rather a relentless manner. 10000 steps each day is not difficult to get to but for most people it requires more walking than they would typically do. One assumption here is that we should be busy consistently expending energy every day and that doing little, being sedentary, is something that we should avoid. As scientists we should always question assumptions. In my field that usually means thinking about the evolution of a trait.
Are we less active than our ancestors?

So what did our ancestors do? When we think about our archetypal 'caveman' ancestors we picture hairy chaps running through the steppes after mammoths with crude wooden spears, burly lasses carrying hide bags of tubers through the forest, and muddy kids running wild across the heath. We look around us and see modern chaps tapping at keyboards, lasses sipping flat whites and kids in x-box trances. It seems fairly obvious that our ancestors were way more active than there modern counterparts. We also look around us and see symptoms of the problems - obesity, diabetes, cardiovascular disease and so on. Sedentary behaviour, despite the bad press, does have its uses: allowing time and opportunity for social interactions (making friends), pair-bond building (keeping a mate), knowledge acquisition allowing specialisation in societal roles (learning a trade or set of skills) and so on. So we do need sedentary behaviour to be functioning humans but perhaps now we have too much non-active time on our hands. If we were more active then we could be more like our mighty-thewed ancestors. Well maybe.

What traits do we inherit from our ancestors?

There is increasing interest in the medical world in doing something about the outcomes of sedentary behaviour. This has lead to some discussion on the evolution of sedentary behaviour and whether it is now a maladaptation in modern societies, an adaptation that was useful in the past but is no longer effective or appropriate, like our craving for salt. In a paper on 'Sedentary behaviour and chronic disease' published in Perspectives in Public Health, Mike Hamlin, a sports and health researcher here at Lincoln, and I discuss this point. We looked at studies made of activity patterns in hunter-gatherer societies that have survived into modern times. It turns out that total daily energy expenditure between modern humans and hunter gatherers is not significantly different. Patterns of daily energy expenditure are different, in that our ancestors alternated days of high energy expenditure (chasing mammoths) with lots of days just sitting around (probably chewing the fat from the mammoths). Modern energy expenditure is a lot more even between days, without the extreme peaks and troughs (apart from prehaps the teenage phase?). One conclusion from this body of research is that problems like obesity are not necessarily because we have become more sedentary than our ancestors, but rather that we have much higher access to consummable calories. Another conclusion, backed by new research, is that short bouts of high intensity activity provides greater protection against chronic health problems than bouts of longer duration low-intensity exercise.

So is my wife doing the right thing with her pedometer which encourages low-intensity exercise everyday? Probably not if she wants to become a mighty-thewed cave-woman. However, living in a modern society, it's a whole lot better than doing nothing extra. And you get to lord it over your colleagues when you take more steps than they do each week!

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