Erm, another good reason left out of this discussion is environmental carrying capacity. If things didn’t die naturally, they would eventually overpopulate the region and die from starvation, habitat loss, conflict, disease, etc. Facing such conditions, a relatively rapid breeding short lived organism has better odds of survival (not to mention mutation). Longer-lived critters die of other causes - there was no evolutional advantage to devoting so many resources (in terms of keeping the body running at peak efficiency) to long life.
Fact is, a breed of immortals would kill themselves off before too long.
Things die because all things fall apart. All systems run towards collapse and require external energy to keep going. By necessity living systems have developed various methods of energy intake and self repair with that energy. Various time lengths are the product of different system structures and different repair strategies, evolving in response to environmental and reproductive pressures.
People, in general not in this thread in particular, seem to think by default things continue as they are. This isn’t true. It requires a great deal of effort to keep things the way they are.
One thing I noticed about this thread, and that I’ve noticed in other threads, is discussion of environmental pressures as reasons for certain adaptations. I’m not sure this is good terminology to use. I think it clouds the issue but I do agree with most of the pressures mentioned as contributing to weeding out adaptations that would allow living things to live longer.
It’s important to differentiate ageing and death in this context. Ageing is the physiological processes that occur in cells as they grow older. Death is simply the cessation of life through any means. It’s perfectly possible to have death without ageing
If your asking why death occurs, then its fairly trivial. It’s the same reason machines break down. Sooner or later, a rock is going to fall on you or your going to get in a car accident. Most scientific estimates predict that death would normally occur around age 400 or so without ageing, more if we lived a safer lifestyle.
Ageing is a more complex matter. There is a part of out DNA called telomeres that shorten every time our cells replicate. Once these run out, then cells have great trouble replicating again. IIRC, this is usually after 20 replications. So evolution seems to have a built in biological clock for all of us.
But that doesn’t explain WHY we are DESIGNED to eventually die. Requiring external energy does not mean that a self-repairing system could not run indefinitely as long as that energy is available.
Pretty much exactly what I was thinking. Evolution would weed out any species that did not have a “self-destruct” mechanism since such a creature would overpopulate it’s habitat, eat the entire food supply and then the whole species would die.
As a side note, I’ve often wondered about the social and economic ramifications if humans were immortal (or lived 400 years when they should statistically die from some accident or disease). It’s a sure bet we couldn’t retire at 65. Would we feel less inclined to “make something” of ourselves if we had 200 years to master somthing? Would people extend adolesence and young adulthood for decades (instead of into their 20s) if their wasn’t such pressure to procreate by their 30s? Or would it be less of a big deal since there would be plenty of time after the kids grow up and move away?
Interesting questions - I think that we are actually already seeing this happen. In the past few decades, “adolesence” has been effectively extended to around the age of 25, as kids are more likely to go to college, and to live at home. Additionally, with the social security crunch, many people are working until they literally can’t go anymore. The retirement age is going up.
So it seems, as we get older and medical technology allows us, we spend longer periods in education (compared to the “finish grammar school and get to work on the crops” society of old) and longer periods of functional working.
Given living until 400, I would agree that we would slow down a great deal, spending longer times being educated and maturing our world view before being considered “adults.”
But all of that is a hypothetical and utopian aside. In any event, it would lead to massive amounts of overpopulation. Being healthier longer is not necessarily a good thing, until technology is able to catch up and provide resources for us at a matching rate. Look at what is happening in India and China and Korea, for example - massively spreading diseases, limited famine, destruction of social boundaries… it doesn’t bode well for the future of humankind. In the end, it may result in condinuted stratification of the classes, and eventual health disparity, where the wealthy live longer and healthier with medicine and better health care, while the poor suffer from malnutrition, diseases, and urban strife.
Interesting points everybody. I can see why there would be selection pressure against long lifespans and in favor of rapid procreation.
For a stable equilibrium, more of one would have to be accompanied by less of the other.
Still hoping that one day we can arrive at a different balance/engineeringcompromise between the two, by applying “intelligent” (or rather, human) design decisions to the process.
And yes, you bet I’d be tempted to extend my adolesence and young adulthood for decades!!
I had a different post but I think it was too long and defensive. Instead I’m going to try and lay out my position a little more clearly.
The question of the OP seems to me to be about two related issues. “Why do individual organisms die?” is the first and “Why don’t immortal organisms evolve?” is the second.
The second issue has to do with the fact that evolution started from scratch. It builds and builds and builds and has no plans or goals or head start. The result is the accumulation of genes that are bad from a human point of view. As long as they don’t hurt their own chances of spreading they spread. Thus immortality, if it were to develop, would not have a propagating edge. Repair systems developed of course, but they are only as efficient as necessary to allow the genes to propagate. The existence of a range of ages for “natural” death to occur in shows that there is room to work with to breed towards longer and longer lives. This is not however a factor in sexual selection in any species that I know of.
The first issue has to do with the fact that no system is perfectly efficient. The self repair systems need self repair. Self repair causes waste, as does the waste removal systems. Every solution produces a new problem or aggravates an old one. The chances of something going wrong increase and as more things go wrong it becomes harder to fix them. Certain problems do not have natural repair systems and when these problems arise death becomes that much closer. Things fall apart and even with sufficient energy this can only be delayed so much. Even external aid cannot stop it, because that external aid will to start to fall apart. If we are considering a hypothetical near perfect system, living or otherwise, then yes it is possible that energy considerations will overtake design ones. Or rather that the extended system collapses first, that is the support systems for the one we are considering collapse and then the one we are considering does.
This last bit leads to the link between the two issues, why don’t living systems that are limited by energy supplies and not their own structure exist? Even by evolutionary “luck” or perhaps tampering (though they would have to exist in a future time, presumably)? This, and a biochemist or similar type may well blow me out of the water here, has to do with the materials that living systems are made from. Clean waste is not in the cards for living systems. Clean waste, in terms of waste that is non-harmful, is needed for long lasting systems. If the waste of a system damages the system that system fails faster.
I think this question is just a part of the “Why aren’t we perfect beings?” question, mentioned by another poster in terms of being strong enough to kill mammoths bear handed. Evolution is not the game of build the best but of build the good enough. All living things are just good enough.
There are some individual plants and trees that have existed for thousands of years by growing a system known to cover hundreds of miles, and some spreading multiple above-ground arms.
Such lifeforms could reach near-immortal status, given enough space to grow. Again, the only thing that stops them is overuse of resources (running out of nutrients in the soil, for example). They are greatly aided by the simplicity of their structure and constant growth. For the great trees, they are limited by the constraints of gravity aboveground.
Given lack of outside factors and sufficient energy supplies, I think it would be safe to say that such lifeforms could continue growing until they simply ran out of space, instead of following a life-death cycle as we know it.
In the end, the answer is the same - environmental variables, carrying capacity, resources, and other factors make “immortal” life unrealistic and a waste of resources, from a biological (not to mention, societal) point of view.
Not to be harsh, but I hate when we allow science to start extrapolating its new-found knowledge far beyond its reasonable boundaries of application. This is one example. Next thing ya know, they will find genes linked to how we pick what cars we drive, or if one puts on a sock and the other sock vs. a sock and then the shoe!
What? Like you can’t possibly die of biological causes until after you reproduce? (Is this written in stone somewhere?) Let’s look at the adult male.
How does that one male sex cell actively involved in forming the zygote know to transmit this information back to all the other cells within the biological father that “It’s ok, pal. you can all die now.” And, how much reproduction is needed to start this death transmission? If this theory held water, wouldn’t we find males who sire kids left and right irresponsibly to be dying faster than the responsible fathers? And, are you suggesting masterbation shaves years off one’s life?
Also, what about the babies who die during infancy? What about elementary and teen kids who won’t live to see adulthood due to various genetic diseases -bad breaks in the genetic craps game of life? Are we all so vane to thing life is so sweet and kind…and it’s all centered about reproduction…and best yet, genetic theory can explain it all? Luckily, my above examples are not the norm or else we’d be extinct. Still, what is it that makes people think life is so kind and biologically ordered?
Huh? Where is this stat coming from? Can we really know what our “potential lifespan” is? Based on the suggestion that genetics is controlling this, where do environmental factors fit into the equation? And, is there one individual amongst us on this planet to form the control group whose arteries are as pure as the day they were born, or virgin lungs that never touched polluted air from car exhaust or second hand smoke? Not to mention some kind of exposure to solar radiation. Is it possible to really know our lifespan potential, yet alone reach our potential? Maybe there’s one hermit somewhere in the Himalayahs (sp?), I guess! - Jinx
OP: “Someone speculated that genes that injure the organism (plant, animal, bacteria, etc) before reproduction are weeded out through natural selection but teh (sic) genes that injure the organism after reproduction are allowed to reproduce and survive for millions of years, over time these destructive ‘post reproduction’ genes built up in all living things and that is why we die.”
Overall, I don’t see how I am so far off-base. I re-read the OP. In short, you’re saying “death genes” are the promoted (dominant) trait after reproduction. And, in trhe same breath you are saying there’s no such thing as infant mortality, or that the odds of death due to genetics prior to reproduction makes it an astronomical possibility. Sure, tell that to my neighbor who lost his teen son to bone cancer, or all the kids suffering with leukemia. Suddenly, it’s not so astronomical. Besides, the logic to this statement is most puzzling to me:
“…genes that injure the organism after reproduction are allowed to reproduce and survive for millions of years, over time these destructive ‘post reproduction’ genes built up in all living things and that is why we die.”
Allowed to live and reproduce for millions of years? It sounds like you’re saying each generation will live for a shorter and shorter lifespan as these genes “build up”. And in reverse, is this to say the first generation (or so) of early man lasted at least a million years? (As I follow you, I feel you’re suggesting the genes were just starting to build?) - Jinx
The idea was that due to the fact that organisms die young and (indirectly) had no need for old age that genes that contributed to death in old age were allowed to develop and grow for billions of years and that is why all living things die. I didn’t see you address this. As far as the fact that people die before reproduction, the theory is that most genes that cause death before reproduction are weeded out or made relatively minimal as these genes cause death before they can be passed on. Genes that cause problems in old age grow rampant as there are no controls preventing them from spreading.
I never said there was no infant mortality, I don’t know where you got that. I’m saying that, unlike genes that cause death and disease before reproduction, genes that contribute to these things post reproduction age will not have any restrictions on them being passed on from generation to generation.
