[TylerJay]

I'm not buying the Demographic Theory of Senescence.

> Aging is nature’s way of leveling out the death rate, assuring that we don’t all die at the same time. Aging puts our deaths on an individual schedule so we can die at different times; other causes of death tend to kill everyone or no one.

It's a magical "group selection" hand-wavy argument—it sounds nice and is kind of heart-warming, but when making an evolutionary argument, that's usually a bad sign. In this case, it doesn't provide an explanation of how purposeful aging could possibly increase an individual's probability of passing on their genes.

If not aging was an option, you would expect to see something more similar to the results of Michael J. Wade's 1976 experimental attempt to show group selection behavior in individuals of a species. He artificially induced resource constraints on a selected subpopulation of flour beetles to see if the beetles would restrain their reproduction for the benefit of the group. What happened? The adults started eating the young of the other adult beetles.

http://www.pnas.org/content/73/12/4604.full.pdf

I don't have an explanation for aging, but I seriously doubt that it's a way for Nature to regulate population size to avoid resource depletion for the group.

[soneca]

I'm way out of my league here, but what if aging is just the way to evolve and adapt. If there were no natural deaths, beings with the same genes would be around forever, with no possibility for its species to adapt to a new environment.

Any reproduction would be just creating more competition for resources if one expect to live forever. So there would be no deaths, but also no births, no mutations.

If there was no death we still would be just - what is the first life form to age? protofishes? populating the oceans until the salinity (?) changes and we were all dead.

[TylerJay]

Hey, sorry for the delay on this. That's not quite how natural selection works, but it's a very common line of thinking. When making an evolutionary argument, you can't make "top down" arguments. You have to look at it from a "bottom up" perspective.

Lets analyze the scenario where individuals don't die by aging. So we have some members of the species from generation 1 who grow up, then reproduce. In generation 2, there are some that have mutations that make them more suitable for the environment and some that make them less suitable. The less suitable ones are outcompeted and don't survive, the normal ones mostly group up to survive, and the ones with beneficial mutations outcompete all the others, leading to the deaths of some of the ones with the "original" genes, and procreate. This then happens again and again with beneficial mutations and they eventually becoming ubiquitous in the population.

There's just no way that an individual member of the species with a mutation that gives it a definite lifespan has a fitness advantage over the others, all else being equal. What's more likely is that immortality is not necessary to pass on genes, so it simply never developed because it would involve many complex systems, the individual components of which would not have conferred enough of a fitness advantage on their own to become universal in a population. And since the natural environment is harsh and predatorial, most animals don't die of old age anyway, which again limits the usefulness of an unlimited potential lifespan.

[drcomputer]

Yea, coming from the background assumption of "everything comes from the same thing", it seems more interesting to me that we have consciousness to experience, rather than the curiosity that we age and die. Age and death are phenomena we observe of ourselves, a thing that is constantly changing yet fundamentally the same thing.

It's a philosophical quirk, but it really depends on your existential and universal (philosophies / beliefs / religions). Things you must assume, basically, in order to make meaning from what is otherwise, pure logic (structural arrangement) and pure state (instances of that structure).

The idea that aging and death are undesirable is a complex phenomena to begin with. A rock does not care that the water slowly washes it away to shape it into a new form, yet humans have very discerning opinions on the matter across all phenomena they observe. Every explanation humanity manufactures seems to have some bias.

[Umn55]

>it seems more interesting to me that we have consciousness to experience,

Everything that is alive has some level of "consciousness" aka some ability to sense, detect, and adapt to it's environment. The idea that consciousness is "special" and "unqiue" is the big lie. If knowledge is unified, then that means the same is true for the universe, since what we call "knowledge" is in fact the universes structure directly. Like your hand, your car, etc. What we call "knowledge" is our representations (symbolic languages like math, english, etc). We confuse our symbols with reality.

It's not that knowledge is "provisional" (aka the structure of the universe is the truth, hence not provisional), it's that our current abstract representations of it is.

[mitteldorf]

Yes, it is group selection, and group selection has been badly maligned for almost 50 years now. But a large body of literature confirms group selection. See David Wilson's book, Unto Others. Group selection is especially effective in the case of population dynamics. See Michael Gilpin's monograph, Group Selection in Predator-Prey Communities.

And the Demographic Theory has been validated in computer models http://mathforum.org/~josh/LogiSen-EER.pdf and http://mathforum.org/~josh/PRLS4Oikos.pdf

[exratione]

Here are a grab bag of overviews on evolutionary theories of aging, of which there are many, and these don't even cover some of the more recent epicycles, such as explanations for runaway longevity competition in some sessile species:

http://www.senescence.info/evolution_of_aging.html

http://longevity-science.org/Evolution.htm

http://en.wikipedia.org/wiki/Evolution_of_ageing

Group selection isn't as dead as you might think; I've seen it show up in a number of places in evolutionary considerations of aging over the years. But then the field of aging as a whole is very reluctant to let go of any of its hypotheses.

Insofar as there is any consensus on the evolutionary reasons for aging in multicellular organisms, it is along the lines of aging providing a necessary state of life history to provide a selection advantage in conditions of environmental change. Functionally immortal or at least negligibly senescent species clearly can exist, as there are some in the wild at present, but in near every niche that life history option has been outcompeted by aging species. Here is one expression of that idea, which again you'll see is veering into group selection:

http://arxiv.org/abs/1103.4649

"Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes."