Human Life Span & Evolution

Is it? or is the lifespan increases purely 'environmental' in that it is our increased knowledge of medicine and health that allows people to reach their potential more often?Average lifespan in developing countries is not all that much different, so when adverse conditions are present it reduces the likelyhood of surviving to old age.There could be selection for better protection of {children\youth} in populations due to having more able-bodied adults around that would select for the children of those who live {longer+healthy} lives, but this may also select for populations that have fewer children so that they are easier to protect with the resources you have available.And it may select for populations where children take longer to reach maturity. Some estimates put humans at reaching self-sufficiency at age 10 or so -- compare this to other ape ages or even other mammals -- and that isn't even reaching sexual maturity yet (13?).Selecting for fewer kids and slower growing kids could select for increased age in adults to compensate for the loss in offspring productivity, as those who were shorter lived would not live long enough to protect the last batches adequately, putting more strain on other members of the group (or increased abandonement).Isn't there some general relationship between the time it takes for young to reach maturity in a species and the length of life of the species (at least for those where the young are cared for by at least one adult)? Consider elephants for instance.In animals where there is no 'penalty' for taking care of the kids (say alligators and turtles?) increased longevity of the adult would be selected for by reproductive advantage, yes?

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RebelAAmerican.Zen[Deist
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Yes, I didn’t mean to imply that had to be necessarily the case.
I was just musing about what might select for longer life and what the consequences might be. Obviously, there are human interventions that extend life, but then human activities/technologies/social norms etc. are now all important selective forces in our adaptive topography. I don’t think kids are growing slower or maturing later (if anything, maturing faster) but I do believe that as we are required to invest more and more in each child (in western society anyway) this will cause selection to favor having fewer of them. This is ”r’ versus ”K’ selection in life history. Longer life is associated with ”K’ selection, K being the carrying capacity of the environemtn for that species. K-selected organism take longer to mature, have low fecundity and live a long time. In contrast, r-selected individuals are selected to maximize their intrinsic rate of increase ”r’, which results in them maturing quickly, producing large numbers of offspring with little investment in any one, and living a short life. There have been many criticisms of this conceptualization (primarily there are no common units of measurement to quantify) but it is still a useful descriptive contrast. There is always a cost to parental care because the parent is csacrificing energy and resources that could otherwise be used to produce additional offspring. But your other suggestion is interesting. In strict Darwinian evolution, there is no selective advantage for increasing longevity beyond reproductive age, and yet it is possible that if parents contribute to their offspring’s reproductive success late into life, there would be advantages for increasing parental longevity beyond reproductive age. Think about how many grandparents are important providers of child care for their kids. Edited by EZscience, : No reason given.

I was thinking more in terms of on the way to modern human, say up to 200,000 years ago when Homo sap got his\her first legs.Looks like sexual maturity is reached about the same time for chimps, bonobos and humans:
National Geographic Article on Gombe (click)
San Diego Zoo Article (click)
Animal Info - Bonobo (click)
12 to 13 years.When we compare old ages of chimps, bonobos and humans we see 40 to 50 years for chimps and bonobos, comparable to hominid ancestors, but twice that for modern humans? I was thinking more in terms of subsets than the whole range - comparing all species that cared for young for instance - to see if more can be teased from the data. I ran across this article:
YES Magazine Article - Respecting Elders, Becoming Elders (click)
But haven't read it enough to evaluate how much valid how much opinion. But read the "First Grandmother" section eh?

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RebelAAmerican.Zen[Deist
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I'm just courious. If an early human was dated to have lived 800+ years by modern dating methods, would that date be scientifically accepted, or would it be thrown out as being incorrect. Would the archaeologists discard it because it's unreasonable compared to the majority of ages?

I don't think that is likely to happen, but in the case of a highly anomalous result like that, it would not be imediately accepted. It would have to be repeated and confirmed through independent testing by others, preferably using alternative methodologies.

Dating methods wouldn't bracket the age of a fossil with anything like a valid number, if this is what you are meaning -- we can't date when an organism was born, and only 14C dating method relies on the decay of 14C to measure how long ago the organic sample stopped taking in atmospheric carbon (to date when the sample died). Dating the layer under the fossil could easily provide a false "life" of thousands of years - heck we can walk on rocks that are over 3 billion years old eh?The methods we have to judging age at death are fairly limited and are based on our medical knowledge of human and animal changes with age.In order to arrive at a theoretical age of 800 (normal?) years for a fossil there would have to be some rather extraordinary aspects -- all teeth there, but worn down to a nub, severe arthritis, the loss of all cartilege in joints and the subsequent wear on the bones, etcetera.The fossil would be more likely regarded as deformed and diseased than old.This is based on applying the tests for age on the fossil to actually test out to 800 years old, rather than taking 800 years and seeing how they would not test to the right ages.Does that answer your question?

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RebelAAmerican.Zen[Deist
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So even if the individual had lived an 800-year life, we may not be willing to admit it? So if the individual had been an extrememely healthy 800-year old man, we wouldn't see these signs. Would we then date the sample as being very young? So then the answer is "yes?" If we did date an individual to be 800 years old, we would look for other explanations instead of accepting the 800-year old number.Trék

Yes, this was one of my points earlier in the discussion. Its a good one, and is yet to really have a good answer.Matt

"Extremely healthy" would allow a person to live to 90 instead of 40 or 50 years, but it would not decrease the wear and tear on teeth and joints, that would still be progressive. No, this is taking the tests we have for age and then extrapolating what the results would be for an 800 year old specimen, independent of health. We would then look at that specimen and see what could be concluded -- and as I said we would see "some rather extraordinary aspects -- all teeth there, but worn down to a nub, severe arthritis, the loss of all cartilage in joints and the subsequent wear on the bones, etcetera."What we would likely conclude about age at death is that it would be indeterminate due to the {excessive damaged and crippled} ("EDC") condition of the specimen.The age dating methods use cross-references between age and wear that we have accumulated (including references to mummies and other ancient bodies where the age is known). We also have correlation checks with juvenile fossils that show wear at these rates, while the bones are still not fully formed compared to adults in the same populations. These latter fossils rule out cultures with excessive wear pattern due to culture specific behavior (say eating sand) because the increased rate shows up in the young population.This means that to posit an over 10-fold increase in age from what is know that you need to have some mechanism to reduce wear and tear well below normal levels.You need to assume a supernatural explanation for how they age without showing it in order to show evidence for a supernaturally aged fossil. This is begging the question.Now I don't really see the use for speculations like this, because they are all "what if" stories, and the "what ifs" can go on for whatever.If there were a population that had a high incidence of what appeared to be "EDC" fossils -- all having the same characteristics of excessively worn teeth and bones and the like, then there might be cause for {investigating\theorizing\speculating} why and how this came to be.There isn't.If that population were also mixed with others of intermediate ages that showed a clear progression from normal young age to the "EDC" fossils with normal patterns for the very young and sufficient intermediates between them to fill the demographics necessary, showing intermediate stages between normal adult wear and the "EDC" fossils, then you might have evidence to consider an old age.There isn't.If there were a number of isolated fossils that showed "EDC" characteristics you might have cause to speculate on an old age.There isn't.The worst we have are fossils that cannot be dated because there is not enough there to provide the data. This of course proves that an old age is possible ... (if that is what you NEED to prove to yourself at all costs so you can be comfortable with some belief or other anyway).Also see {Bone Maturation}
Bone age - Wikipedia
Page not found - Image Sciences Institute
for fairly accessible articles on some of the changes in the skeleton structure with age.As long as all of the markers that we have for age development occur in normal patterns you cannot then assume some fantastic age for those fossils.Now consider Histomorphometric age assessment of the Boxgrove 1 tibial diaphysis: Notice four things:(1) They can measure age up to 55 years by this method -- not just juvenile development.(2) They also correlate this with samples with teeth wear to show that they have the same age (they didn't have to, and in fact there is a slight difference).(3) There are other methods for estimating age-at-death.(4) This paper is discussing the accuracy of the estimates, the correlations that validate the age estimates and how to make those estimates better.See Dynamic bone remodeling in later Pleistocene fossil hominids. for another early hominid age-at-death study (abstract only).See also {Dinosaur Fossil Bone Leads to Gender, Age Determinations } and {X-ray microanalysis of fossil dinosaur bone: age differences in the calcium and phosphorus content of Gallimimus bullatus bones. } for some other information related to estimating age-at-death.Enjoy.

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RebelAAmericanOZen[Deist
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Surprisingly I don't think this thread has really touched on the theories of the Evolution of ageing too much, so I thought I would just quickly point out a few things worth reading.I wrote a paper myself on this about 3 years ago which is a basic introduction to the concept of the evolutionary context of Ageing (Research, Innovation, Risk Taking and Living Forever: Why Do We Age?). What this paper can probably used for more than anything else for interested parties is the references I have used. particularly worth reading is this paper: shortened link which although it is quite dated now (1957) it still strikes a key theory in the evolution of Ageing and is (for me at least) such a good read.This doesn't pertain to evolution of human ageing exactly, but the overall concept of evolution of ageing should be no different to humans as it is to all other organisms.A few other thoughts I have had as I have read through this thread are: 1. Humans are not really living longer today than at any other time, we simply have a higher statistical age brought about by not dying early. Our theoretical maximum life span seems to be static.
2. ImmInst.com is for sale | HugeDomains is the place to look at if you want to learn more about lifespan because there are a lot of people out there who think science will be able to extend our lifespans artificially in the not too distant future. There is therefore a lot of good material on that site about human lifespans.ShaneEdited by AdminJar, : No reason given.

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Thanks Shane,I notice that the second link can be shortened to
Telomere.orgI also noticed recent reference to the "hobbit" fossil as a 73 year old woman that lived 18,000 years ago
http://dsc.discovery.com/news/2006/08/21/hobbit_hum.htmlAnd have seen other references to old people in ancient sites and that indicate that such age is not outside the possibilities for those people.Thanks.

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RebelAAmericanOZen[Deist
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