Today there are several lines of research under way that are treating both the infirmities of aging and the aging process itself, so that we are treating many of the phenomena like loss of memory, loss of vision, sexual performance, and so on with individual therapies, and in the course of that we are essentially extending the quality of life for people at a much higher age. If one then in addition looks at the current work on stem cells as well as on certain phenomon like telomerase, an enxyme in DNA, what we find is we are learning a great deal about how that mechanism is the control mechanism for aging, and it is very likely that over the next 25 years, we will be actually be able to manipulate the production of telomerase in individual cells. In other words, society will see serious and effective medical intervention in the aging process---people undergoing such therapy will keep looking and feeling and acting younger than their calendar age. The prospect to individuals for living seriously longer than the current norm will begin to open up.

The Hayflick limit is the limit of the maximum number of cell replications that a human being (or any species) can engage in. So, how many times do our cells replace themselves? That's the limit of human lifespan. When you can't replace your cells anymore, you die. And Leonard Hayflick calculated that number for a variety of species, and for human beings it was 120. So we have almost no documented instances of people living more than one hundred and twenty years.

Science and medicine will not only be essentially extending people to their normal full life span (i.e. 120), but will extend the human natural life span to beyond that, and a reasonable guess as to how much will be gained over the next century or so is at least 25 or 30 years. In other words, a person born in the year 2000 will still be alive in 2150 There's one other factor. If one simply looks at the historical trend, one finds that over the last century, we have nearly doubled human life span. The average lifespan of human beings (average, not maximum) has gone from about 45 to about 85. With the advances in microbiology and molecular biology, there's no reason to imagine that we won't do at least as much in the next century. In fact, if you double 85, you're at 170... so I'm actually being conservative.