http://www.nytimes.com/2006/08/31/health/31age.html?pagewant...
I'd be glad to believe that genes matter, because my grandparents lived long, healthy lives, and one of my parents is still living, but I think my ancestors had rather different lifestyles from mine.
Evidently "extreme longevity" is more heavily dependent on genetics than non-exceptional lifespans:
"Perls and coworkers originally found that the survival ratio for siblings of centenarians versus siblings of 73-year-olds was about fourfold for ages 80–94 (79). In a more recent assessment involving 444 centenarian families, these investigators found that, compared with the U.S. 1900 cohort, male and female siblings of centenarians were at least 17 and 8 times as likely to attain age 100, respectively (80). Similar findings of a much stronger heritability of unusual longevity have been obtained by Kerber et al., who demonstrated an increased recurrence risk for siblings for surviving to extreme ages (81), and Gudmundsson et al., who found that the first-degree relatives of probands who live to an extremely old age are twice as likely as controls to survive to the same age (82)." [1]
_
1. Annu Rev Med. 2005;56:193-212. Quote is from p205. http://pi.edu.pk/donald/genetics.of.longevity.and.aging.pdf
In these studies, identical twins who are adopted and raised apart have just as much correlation in lifespan as identical twins raised together, suggesting that genetics (rather than family lifestyle) is the cause of the correlation.
Personally, I don't mind the James Dean ethos: "Live fast, die young, and leave a beautiful corpse behind!" :-)
You'd think it would actually be in the best interest of any given organism to have as long a reproductive lifetime as possible, and therefore fitness would increase along with longevity, as long as that longevity remained virile/fertile.
Then again...
If the old did instead survive to compete with the young, evolution would start to fail as a process—you'd have too many non-adapted organisms reproducing with one another, and so what adaptation there was would happen much more slowly.
Today, sexual species that have "dropped back down" into being asexual, reproducing by cloning or the like (which have the same evolutionary disadvantage as a non-aging species would have, but more so) can survive and prosper. However, far enough back in the genetic soup, when sexual species first diverged from asexual ones, there was probably a fierce competition where being a sexual species was only a little better (it requires more resources, after all), and so aging provided an immediate advantage in terms of setting an equilibrium point for species size, so as to not strain resources.
(This may very well be taught in an intro Bio class, but I love discovering things on my own in the form of meditative writing. It's a fact completely untaught in schools today that knowledge lies at your fingertips that you're completely unaware of, not from a book or a website or another person, but from your own mind, and that you can access it without having to have anyone guide you to it. Philosophy is neglected as a means to pursue ordinary, practical knowledge, but it's really just a super-set of science: there's still a hypothesis, experimentation, observations and a conclusion, it's just that the "experimentation" doesn't require a physical world. In the case above, obviously, it would be better to have an actual scientific study, but the very fact that you can derive a preliminary intuition of a topic without anyone telling you what to think, or giving you a demonstration one way or the other, is revelation enough for most people in the world today.)
The old surviving to compete with the young would not make evolution fail. There are limited resources and competition for them so the ill adapted die, there's nothing in there that stops the old living on forever, and if organisms can't breed together they generally don't copulate (adaptation). Great^8 granddad might want to get it on with g^8 daughter, but she'll be uninterested because her adaptations will not see him as sexual, any more than we'd see a chimp.
There is actually only one major family that are asexual the rotifers. Given that sex appears wasteful of energy, the fact that there is only one example of a lineage successful in geological time with asexuality is pretty strong evidence it's a good idea.
For more, better, more clearly expressed, read Richard Dawkins.
Under no circumstances read anything by Steven Jay Gould to learn biology.
Women who stopped having children and instead invested in their grandchildren had more decendents than women who didn't stop having their own children.
Indeed. However I studies philosophy when I was 14 and I suspect it may be due to this early "training" that I am incline to think stuff through on my own and get a logical understanding of things. I have been pleasantly surprised often by so many things I have come up with on my own to only find out that many other people with proper objective undertakings have arrived at the same conclusions, or things I thought were knew and insights to only find out others are studying it indepth.
I think people do not try and think stuff through on their own perhaps because they have not been giving this "early training". There is a danger with thinking stuff on your own and that is the fact that one may come up with whatever story, which is perhaps another reason why laymen may disincline to endeavour in such activity, however if they were introduced with some philosophy and emphasised the objectivity of their undertaking our place perhaps would be filled with much better adapted individuals. For such reason I propose philosophy be introduced in the curriculum at grade 9, rather than religion as they teach here in Britain.
The theory of evolution speaks of adaptation to the environment so that one may survive. Whether they want to survive only so that they may pass on their genes is only a hypothesis which sounds rather convincing, but there is hardly any evidence for it. There is no reason to assume that we only live so that we may reproduce, although reproduction is an important part of our existence.