Discussion of everything related to the Theory of Evolution.
To Butterfly1, I agree with Biohazard, it makes no evolutionary sense for an organism to be programmed to die in order to give more room to its offspring. If dying is a given, though, it may make evolutionary sense for an organism to sacrifice itself for its offspring. I think that if there were genes that made it possible to live and reproduce forever, and there was an evolutionary path to those genes, life would have found it.
I think that women live longer than men because of the grandmother effect mentioned above, but also in primitive societies, men are expendable. 10 women and one man means ten babies next year, 10 men and one woman means one baby next year. A tribe cannot afford to lose many of its women, but it can afford to lose many of its men. Thats why in primitive societies, men are more likely to wage war, not women. There's no reason why that value system should not be encoded in the DNA to some extent.
Excellent words there.
But in a way life has already found a way for an organism to life forever, or at least for a very long time. This can be seen for example with bacteria or plants. A bacterium in a suitable environment essentially lives forever. Admittedly, it is hard to keep track who or what is the first bacterial cell after several cell divisions, but the point is that those organisms do not die of old age. Instead, they simply keep dividing on and on. Of course one could argue that dividing indefinitely is not living indefinitely when it comes to any single organism.
But if you consider plants, some of them (most notably trees) do not exhibit this animal-worldish way of reproducing a finite time and then stopping it and dying. Instead, trees keep producing offspring for long time, some of them hudreds if not thousands of years if nothing happens to them. Of course, in the end they die too, but it is bit difficult to tell if it is "old age" or something else :)
Anyway, what I'm trying to say is that ageing must be a sum of many things, and none of those things alone is something that cannot be avoided by the tools evolution has given to organisms. Together, however, they make creatures die of "old age" - some later, many sooner!
From the evolutionary point of view it is quite interesting that often males and females are born in approximately similar numbers despite the fact stated by Rap, that you only need a few males to fertilize dozens of females, or even more. In many species this obviously has a lot to do with competition: the nature makes males to fight for their right to have offspring, thus ensuring that the best genes survive. But if so, why not make 2/3 males and 1/3 of females to make the competition even more fierce? Or make 1/3 males and 2/3 females simply to allow for more babies to be born. Also, human males are born at a slightly higher rate than females, is this because more males get themselves killed before they reach adult age?
It seems what you're looking for is the evolutionary rationale for aging, which is what really clears the field for offspring. But not every organism ages. Even discounting asexual reproducers (as mentioned above, how "old" is a bacterium?), why is there variation in sexual reproducers?
The reason for equal numbers of males and females is differential evolutionary pressure.
If there are normally more females, which seems the optimal reproductive ratio, then there is an evolutionary advantage to producing more males. So evolution supports those who make more males. In the long run, it all balances out with equal numbers of male and female offspring.
Last edited by skeptic on Sat Feb 05, 2011 7:27 pm, edited 1 time in total.
Yes, if organisms could live forever, why should there be aging? "clearing the field for offspring" does not work, because why eliminate one reproducing organism in favor of another? If an old organism has demonstrated fitness in dealing with the environment by living to an old age, why should it be programmed to die in favor of other younger organisms who might not be so fit?
An idea that intrigues me is the "red queen" effect. An organism is born with a set of genes to combat disease, parasites, predators, etc. (DPP). The DPP evolve to counteract these defenses. So its a genetic arms race, and the older an organism is, the more subject it is to newly evolved DPP.The organism species must keep evolving just to stay even with the DPP, like the red queen tells Alice that she must keep running just to stand still. At some point, it makes no sense to encode longevity, it won't work anyway. But, unless encoding longevity brings some kind of penalty, why encode for lack of longevity?
Actually it's statistically proven that women live longer than men! Look around and you will notice men do a lot of heavy jobs which wear the body out more quickly. This also due to a deeper factor involving the blood. You see, women tend to have an iron deficiency because of menstrulation. The iron in our blood equals age for our cells, and because men have more iron, their cells age faster. Also, women tend to vent their frustration better then men because men are often taught to internalize their emotions, which leads to stress. So yeah. Now you know
Speculation does produce some interesting thoughts.
Serious research does however point us in a direction that has some answers to this question
Thomas Perls & Ruth Fretts have done some such serious research.
They are summarised here
http://www.cmu.edu/CSR/case_studies/wom ... onger.html
An extract (with my emphasis)
"Men and women alike have seen profound gains in life expectancy in this century. Since 1900, the average national increase in life expectancy in developed countries has been 71 percent for women and 66 percent for men. This increase cannot be explained by physiological or evolutionary theories. Rather, swift changes in knowledge of health and disease, changes in lifestyle and behavior, and advances in medical technology have greatly improved the chances of both sexes' living to old age.
In the past two decades, however, there has been a notable deceleration in the extension of life expectancy in women. The reasons for this decline are still being debated. Some researchers feel that women in developed countries are close to reaching the natural limits of human life span, and so their gains in life expectancy must inevitably diminish.
But some sociologists have discounted this reasoning, pointing instead to women's changing roles in society. As more women have taken on behaviors and stresses that were formerly confined to men--smoking, drinking and working outside the home--they have become more likely to suffer from diseases that were traditionally considered "masculine." Mortality from lung cancer, for example, has almost tripled in women in the past two decades. Smoking seems to be the "great equalizer" for men and women: current actuarial data from Bragg Associates in Atlanta show that on average middle-aged female smokers live no longer than male smokers do."
This assumes that natural selection happens only on an individual and never on a group level. But there is plenty of evidence that that is not the case and the mechanism is easy to visualize. Given a population of a species that had no reproductive controls/generational turnover versus one that did, the sub-population with the immortal individuals would overbreed, exhaust the resources of its local ecosystem, and perish, leaving the other population successfully outcompeting it and passing on its genes for mortality. The selection has to happen at the individual level but what impacts the group often does impact the individual, so that's not a barrier.
Hmmh. So what is keeping the immortals in their local ecosystem? If the ecosystems are completely separated, there cannot really be any competition between the two groups, can there?
Also, there are many species that are "immortal". For example virtually all prokaryotes do not die of old age, but just keep dividing as long as they can. And they indeed do exhaust all their resources in their local environment if they can and they die after that, because of that. The trick is to constantly look for new environments and only get back to old ones when they can again sustain growth.
So, why haven't bacteria evolved to die of old age in order to conserve their environment? (:
Most certainly, the game is played both ways when it comes to living beings. Some go to the very extreme in terms of quantity and others of quantity. But in the end all organisms must have both numbers and quality to survive, it is just the ratio of those that keeps differing.
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