RH: We think back to our first memory, our first big adventure, and it's almost as though there was a movie camera in our head recording every detail. But that's not the way it is. That's an illusion. What we're remembering is a memory of a memory of a memory, of perhaps the real thing. A man may wear a wrist watch when he's 20 and the same watch when he's 50. It's the same watch but it's not the same man inside. Every atom in his body has changed, has turned over. I'm not the child I once was. The child I once was is dead.
Irving Kahn, a financial trader on New York's Madison Avenue, who has come to work every day since 1927. Irving is 105 years old.
Dr Nir Barzilai: For Irving, and especially for his sister, Helen, she's been smoking for 95 years, two packs for 95 years, which shows you that if you smoke for 95 years, you live a long life!
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So the point here is that our centenarians, as a group, did not interact with their environment the way the doctors tell their patients, that you have to watch your weight, you have to exercise, you shouldn't smoke and you should drink one cup of alcohol a day and all the things we know to tell them. It doesn't matter for them.
RH: So, for some, lifestyle and environment don't play as large a role as we've been told. But if Irving's genes hold the secret to long life, why hasn't evolution given us all genes like his? If there are genes that increase longevity out into the hundreds, why didn't natural selection favour those genes in our ancestral past?
Dr Nir Barzilai: Well, I will tell you, there is something very upsetting in this sense in our group. First of all, a third of the centenarians in the world don't have children. OK, so I don't know, is it having children, raising them, rearing them, I don't know what? But the point is that there is some exchange between reproduction and aging. But also, in my study, the centenarians had less kids at a much later age than my control population. So, if the control population has 3 to 5 kids on average, our centenarians are 1.7 kids on average. And so, if you are thinking that way, we're losing longevity genes, right? Because in every generation, we populate more with kids of the people who don't have longevity genes than have longevity genes.
RH: Our genes appear to trade long life for reproduction.Longevity seems to be connected to later reproduction or no children at all. So how long we live and why we die are dependent on our genes.
