Andrew - Famine is usually defined as a catastrophic shortage of food of such immensity that it's associated with very high mortality levels.
Anna - But how come so many people actually come through famine and survive?
Andrew - Let's start thinking about how the body manages in metabolic terms. The first thing it needs to know is how fat or thin it is, and so there's a hormone that tells the brain that acts as a fuel gauge. When the brain realises that it's very short of food, it starts to save energy, use up body fat, protect the major organs and hence protect survival. There are very clever mechanisms by which this is orchestrated and also some very terrible ones, for instance, cannibalism.
Anna - How come we haven't evolved similar mechanisms for dealing with lack of water, especially as lack of water and lack of food due to drought are often quite highly correlated?
Andrew - That's a very difficult question and one which I haven't thought about before. I guess one explanation is that humans have been clever enough to dig wells. So even if there may not be enough water for the crops, they are generally able to get enough to drink.
Anna - If famine has been such a driving force in evolving what we like and what we eat and how we deal with food, how come we need such a range of foods in order to be healthy? Why can't the Atkin's diet, say, be enough?
Andrew - I think we need to separate out survival and optimal growth and development. If you look back at mediaeval times or people who live in small cottages and hit their head on the beams all the time, you will realise that people were much smaller. So although you could hang on in there and survive, there's a big difference between that and growing optimally, having optimal brain function and optimal survival. That's where the quality of diet is really important.
Anna - While we're on the subject of diets, obviously obesity is becoming a big problem nowadays. Are these adaptations that we've had in the past causing us more problems than just obesity?
Andrew - I think obesity is the obvious where we've got a complete mismatch between our modern environment and our very ancient metabolism that has evolved to survive famine. Diabetes is also though to be a consequence of our evolution against famine because it is associated with the propensity to lay down fat very quickly. So in times of feast we lay down fat and that is regulated by insulin. And then during times of hunger and famine, we use up that fat again.
Anna - Do you think our bodies are going to evolve to deal with fat in the same way that we've evolved to deal with famine?
Andrew - I think that's an absolutely intriguing question. It's a difficult one to answer. To some extent you can argue that evolution has stopped now. We're not trying to have many children and so the fact that it takes a fat woman a lot longer to conceive two children than it takes a thin woman to conceive two children doesn't make much odds. So my feeling is that we won't evolve back again.