Last week on the Naked Scientists you said that we have been walking the way we do for the last 1-1.5 million years. Why do you see so many people with arthritis in the hips and the knees? It's not rare for people who've had major surgery in their hips or knees. Hasn't evolution caught up with us yet after 1-1.5 millions years? Due to changes in our lifestyle is there a difference to 50-60 years ago when our average lifespan was relatively the same as it is today?
Chris - It's a good question. Why haven't we evolved out of getting diseases like arthritis? Why hasn't that gone away, why hasn't evolution given us better cartilage. The answer is, Dave kind of hinted at this earlier. It's all down to having children. If something stops you ahving children then the genes that stop you having children will be removed from the population and genes that help you to have children and live long enough to have children will be enriched in the population. Since arthritis is really a disease of old age – it doesn't tend to come on until you're in your 60s. I think 100% of people aged 60 have some degree of arthritis. It's not till you're a bit older than that even that you tend to have occupational problems of joint damage already that you need major surgery. The reality is that because arthritis doesn't stop you have you children the genes that might make you have an increased risk of it don't get removed from the population. As a result we all have the same risk of arthritis. It's a bit like going bald. Because most people don't get bald until after they've had children as a result we haven't removed that gene from the population. There's lots of men who've got male pattern baldness.