Is aging in adaptive trait? There are several theories of aging. What theory of aging has most support today? Well, I think the studies on evolution were probably the most informative. You have a breakdown in natural selection with a declining role of fitness. So when people reach a certain age, they're not having children or raising children anymore. 

There historically has been less selective pressure to keep those people healthy. And then the question is whether things just begin to break down in the absence of that selective pressure. Or if something like antagonistic pleiotropy is going on, where you have mutations that keep you healthier when you are younger. And the cost is things going wrong later in life. Dr. Brian Kennedy. Dr. Anton Titov, MD.

There are also people that see aging as a program that may be in place for some reason to get rid of the older population or as a consequence of some other pressure. 

So I think we're still debating those kinds of things. It's pretty clear, however, that the selective pressure declines after the age of about 40. And that's about the time you see the onset of age-related changes and chronic conditions that arise from them. In one of your publications, you also mentioned if in several reviews, that despite the natural aging process, it seems like there are several programs that can be easily activated by changing one or a couple of groups of genes. Therefore, aging is not necessarily absolutely programmed in the evolution. 

Yeah, I think the striking thing when I started in the field in around 1990, I think most of the aging field would have said, well, by 2020, we'll know a lot about aging, but it'll be really hard to do anything about it in humans, because it's such a complex phenomenon. And what we've learned is that it's really hard to understand aging, but it's really easy to do something about it. Dr. Brian Kennedy. Dr. Anton Titov, MD.

So there are lots of different interventions now that extend lifespan in a whole range of model organisms. 

They extend healthspan, they prevent age-related disease onset. And now we're trying to figure out why that is. One way to think of it is that if you have something that's already fully optimized, it's really hard to improve upon that, especially by mutating one gene or giving one drug. 

But aging is not under that selective pressure. Aging is sort of what goes wrong after pressure declines. And so it's easier to make things better, because you're starting from this semi-dysfunctional system and trying to improve it. if you want to make a car work better, you don't start with a fully functional Mercedes, where there's nothing wrong with it. 

You start with a used car you get almost in the junk yard. You change the oil, and you change the tires, and all of a sudden that works a lot better. So that may be what's going on here with aging. But the surprising thing is, at least in animal models, it's relatively easy to delay aging, and you get an accompanying benefit and healthy longevity as well. Dr. Brian Kennedy. Dr. Anton Titov, MD.