the hypothesis which says that a species has a relatively fixed rate of ageing from adulthood. the conclusion? that we're unlikely to be able to manipulate that process because of biological constraints. here to explain more is study author susan alberts from duke university. thank you very much forjoining us. i'm a little bit confused because we are living much longer, aren't we? so what is to say based on your research that at some point in the future we may not find the magic pill that allows us to live forever? thanks for having me. i don't want to crush _ thanks for having me. i don't want to crush anybody sold yet. i think it's a _ to crush anybody sold yet. i think it's a little — to crush anybody sold yet. i think it's a little early for that but certainly _ it's a little early for that but certainly their study points to the idea that — certainly their study points to the idea that there are limits to how much _ idea that there are limits to how much we — idea that there are limits to how much we can extend the human lifespan — much we can extend the human lifespan. there's been a bit of a debate — lifespan. there's been a bit of a debate about that. some people say the human— debate about that. some people say the human life span is limitless in others _ the human life span is limitless in others they know. in fact there are limits— others they know. in fact there are limits to _ others they know. in fact there are limits to how long we can live. to tackle _ limits to how long we can live. to tackle that — limits to how long we can live. to tackle that question we actually asked _ tackle that question we actually asked within species and we compared