Evolutionary theory would also suggest that we have some mechanism to ensure our deaths. Longer lifespans cause fewer generations per time period, resulting in less adaptability as a species.
(Of course, we do die. But the explanation looks more like "growing and reproducing quicker beats longevity" than like "planned obsolescence".)
I also think, making grandparents less mobile means they are around the campfire teaching the youngsters. It makes sense it would be selected for in a race of communicators.
Humans can live for decades beyond their most-productive years. Their has to be a Darwinist reason for this.
Thus, the number of healthy years in the wild relates to both the probability of an external death AND internal heath issues. For a mouse this suggests a minimum of internal maintenance for maximum reproduction where a parrot can make significant trade-offs in reproduction in order to live 10x as long and have more long term reproductive chances.
However, that's in the natural setting. A pet (mouse, cat, parrot) can live slightly longer in captivity by surviving pat the point where it can find food for it's self. If you look a human vision decline people are significantly less capable of surviving on their own before they lose reproductive capability. And in that "unnatural" old age it's not uncommon for various species to have increasing reproductive issues.
We evolve because we don't die...we don't evolve so that we may live.
http://www.fightaging.org/archives/2011/03/we-age-because-th...
But the degree to which aging is programmed - versus simply an unhappy stochastic decay due to diminishing selection pressures in later life - is a big and ongoing debate. Some species clearly have a lot of programming going on. For example, salmon age at a rate determined by the laziness of bears near to their particular rivers:
http://www.fightaging.org/archives/2007/12/bear-consumption-...
But there are equally good counter examples for many more species that suggest the situation is that evolution sets up to win the short race, front-loading as much as it can for early success, and then the selection pressure drops off after you had your shot at reproductive success. All that front-loading produces unpleasant later consequences as things fall apart - you're not set up for the long term.
The adaptive immune system is a good example of this - it's a system that could never run as evolved for an indefinite period of time. It's always going to crash and burn at some point, and that's somewhat a consequence of how it's evolved to run extremely effectively right out of the gate in early life:
http://www.fightaging.org/archives/2006/12/when-and-how-does...
For more reading on this topic, you might look into antagonistic pleiotropy - the premature optimization of the evolved world:
http://en.wikipedia.org/wiki/Antagonistic_pleiotropy_hypothe...
All known species die of old age. This includes species that are not social and do not share resources. Group selection can not be the mechanism at play here.
Except, possibly, the immortal jellyfish. http://en.wikipedia.org/wiki/Turritopsis_nutricula
In your example, what stops the genes from spreading is that the entire village dies of starvation or competition with other tribes that have younger, fitter members.
Its a matter of degree. Humans are social to a high degree, but possibly not as high as ants for instance. Ants eat members of the tribe that are injured, an extreme example of group-efficiency taking priority over the individual.
Young people on average, seem to be more acceptant of new technology, where older seem to be less acceptant. Additionally, from personal experience; I think younger people think about problems differently as well which leads to new developments. It makes me wonder, even if our capabilities to develop new technology are growing (Kurzweil's theory of Accelerating change) perhaps the age of both the general population, and the engineers will cause some level of impedance.
Along the same lines, if a growing population requires growing technological change. And my concept is correct, that age reduces technological evolution, is it possible that it also reduces our ability to adapt, and a natural population balance occurs?
I think to change anything substantially, you have to wait for a complete turnover - everybody has to die off, before the seeds of change can take root.
Young people (< 20yrs?) are purportedly more adaptable than older folks, say 20-50. I maintain they aren't really adaptive, they simply have more choices when they learn their first pattern. And they have many patterns to learn, which takes years, perpetuating the myth that they are adaptable.
PS: There is also trade offs involved which probably provided evolutionary benefits to those cutoff ages.
When they want to test learning they find people that don't know something, teach it to them, and test them at all points in the process. They also don't limit themselves to a single type of skill and can measure improvement based on how much they improve over time to measure long term skills acquisition.
Unless they limit themselves to reflex action or some such, it becomes impossible to separate previous learning of anything complex.
I think I give researchers plenty of credit. But they don't often have the time/resources to have many/any controls. When a remarkable correlation appears (like 'students stop learning about when they leave school') I call foul.
If you take 2 individuals and one dies sooner than the later, the alive one will have had more chances to pass his genes, so it's not adaptive to have mechanism to ensure our deaths.
Apparently, it typically is better to create new organisms every now and then. That may just be energetically better or it may be because (in particular, sexual) reproduction allows for faster adaptation to changed circumstances
Only if you assume the non-reproductive members are a net negative (grandparents becoming a burden)
Regardless of reproductive lifespan, in a population that is in equilibrium (not increasing or decreasing significantly), the average number of (surviving and reproducing) children per individual is going to be 2. So supposing we could live to be 1000 years old, and still reproduce at that age, we'd have an average of 2 generations per 1000 years.
It seems that I've seen a somewhat(?) common pattern among people who have young families and get divorced that often times have another family (+2 children) when they re-marry.
This is not true though. It would be true assuming a constant population size or a single offspring. The number of children I have and the number of children my children have has nothing to do with how long we live.
Think of it this way: if you knew you had a high probability of living to 80, you might decide to have fewer offspring so that you could dedicate your earnings to supporting yourself in your later years (children are very expensive after all).
Regardless of whether this hypothesis is true, clearly the number of years you live likely has some bearing on how many children you might choose to have.
Not all animals are pre-programmed for an early death. I wonder if curve for these animals looks like the lightening bolt curve?
http://www.fightaging.org/archives/2007/06/ageless-animals-t...