I thought the discussion about Vijg et al. study on aging was interesting, but I don’t think the panel really delved into what it means that life expectancy (probability that at any given age you will live longer) has increased but life span (total length of one’s life) doesn’t. Kara was arguing that the limit on life span may be due to things like cancer. But wasn't this what the article was arguing against? We can imagine two models: (1) life span is the result of the combined probabilities that you will get sick at some time, (2) life span is determined by some intrinsic process that is independent of this. By the first model, you would expect that as we get better at treating disease that both life expectancy and life span would increase. By model two, you would expect that no matter how good we get at treating disease, this will only increase life expectancy and not life span. Kara’s example of cancer would fall into the first model. She may be right that there is an inherent relationship between cancer and the mechanisms of aging, but simply treating cancer itself would not increase life span -- just life expectancy. As the panel discussed, extending life span would involve going beyond treating “disease” (or redefining the word) and altering the underlying normal processes by which cells age.
Another point that caught my attention was Steve’s argument that it would be hard to renew the brain without causing a change in one’s “self”, and that this imposed a limitation. But I wonder? Don’t our brains continuously change throughout our life span and doesn’t our “self” constantly change with it? What exactly would be lost if we start replacing our current neurons with new ones? Kind of comes down to how we define our “self”. I would argue that whatever continuity we experience is probably an illusion – we have memories, most of which are probably reconstructed, and we have patterns of behavior that constantly change. As long as we maintain an internal dialog and maintain the illusion of a continuous “self” we may be fine. We will change, but I will still be “me” – because that is how it works in real life. It would just have to be gradual. Can you imagine what you would think if one day you were your 20 year-old self and the next day you were your 60 year-old self. You would be in shock at how much you had changed. But if you do it slowly, and it is simply called “life”.