Hello Friends

Are we any clearer on why certain species age and die ? I remember in the Selfish Gene, Dawkins put forward the idea that perhaps certain "death genes" mutated in a very early ancestor and were so successful that they survive to this day, as obviously many organisms still die.

I believe he said something along the lines of, these "death genes" only started affecting the host organism after adolescence, and of course by then, there is a good chance that organism has had sex, and passed on the death genes.

That's one, the other one I've heard is about the Telomeres getting shorter and shorter with each cell division.

Any help and information on this topic would be great. Please bear in mind I am a n00b, so nice clear baby explanations would be awesome.

Thank You.

PS. I know Evolution wouldn't happen if organisms didn't die. But that's not the topic here.

Evolution is easier to understand if you consider it from the point of ecosystems, rather than being about individuals or species.

hehe and about the cause of death bit ?

Are we talking about cellular death or organism death?

Cells are programmed to die (apoptosis) at regular intervals. One of the causes of cancer is that cellular apoptosis is no longer operating certain anti-cancer drugs are been/ have been developed to switch on those genes which regulate cellular apoptosis. IIRC there is one cell line used in cancer research which may be 100 years old and I think from a female.

The death of an organism and here I presume from old age rather than other reasons, then it is a multi-factorial event. We tend to think of an organism as a complete whole, whereas in fact it is a collection of different parts which all depend on each other in order to function at an optimum level.

As an organism lives the cells in each structure divide and die. Eg. Red blood cells have a life span of just over 90 days, so the red blood cells in your body are not the same as the ones you had when you are born, similarly skin cells(epidermis) are shed daily, as are cells of the corneal epithelium some of which are discarded every time you blink. Eventually cellular replacement ceases to be efficient due to problems with telomeres at the same time the bodies organs be less efficient. So eventually the organism dies because the efficiency of the support organs, heart, liver, lungs etc are no longer capable of providing the required functions.

Here, a problem I have often observed in the elderly, is that the gut no longer absorbs nutrients at the required levels. I have seen people in the local EMI Unit over the years just being 'cured' by having three square meals a day. This is the reason that supplements are often suggeted for the elderly in that a person may be getting the RDA but is not able to absorb efficiently and is thus not actually getting their RDA.

Thanks for the reply Ian.

Concentrating for a moment on the death of an Organism. Why does the functionality of the Organs and Organ systems decrease with time ?

I mean if the cells keep on happily dividing into new cells (which I presume happens in all tissues, not just at the epidermis), why is it that the new cells aren't as good !

Thanks

Ciwan wrote:Thanks for the reply Ian.

Concentrating for a moment on the death of an Organism. Why does the functionality of the Organs and Organ systems decrease with time ?

I mean if the cells keep on happily dividing into new cells (which I presume happens in all tissues, not just at the epidermis), why is it that the new cells aren't as good !

Thanks

The act of being involves a constant degradation, for most of us the degradation is balanced by constant repair and renewal. As we age this repair and renewal slows or stops (an area of much research). Death is when the renewal can't keep up any more.
Try to imagine a wooden floor, the every day use results in a build up of scuffs and scratches, but this can be remedied with a good sanding down and repolishing. This process can be repeated seemingly indefinitely, but eventually the more serious damage isn't completely removed and begins to build up. At some point you will have sanded down the wood so much that there just isn't any left to sand. This is death, so to speak.

edit to add summary

The short answer is imperfect reproduction, the very same mechanism that is so important in evolution.

Cool, I understand Imperfect Reproduction.

So why is it Imperfect ? I mean what about it is Imperfect ? Is it all about the Telomeres getting shorter ? or is there more to it ?

Ciwan wrote:Cool, I understand Imperfect Reproduction.

So why is it Imperfect ? I mean what about it is Imperfect ? Is it all about the Telomeres getting shorter ? or is there more to it ?

Well, from what little I know, there's more to it. Damage, from radiation for example, also causes imperfections to increase. Exposure to certain elements and other substances also have an effect. I imagine genetics also has a bearing.

Aging happens to organisms basically for the same reason that say, a car rusts or a building becomes rundown. It's basically the default state of affairs for any system; things will tend toward a state of disorder, unless energy is being expended to maintain them in a state of order. Throughout an organism's lifetime, things will go wrong - basically, nearly every chemical reaction required for life will also result in deleterious side reactions, with the result that damage will accumulate over time. Of course, we have a lot of mechanisms for repairing some of that damage, but natural selection will basically only apply selective pressure towards acquiring damage repair mechanisms to fix the sort of damage that might kill us before reproductive age. Which basically means that there are a whole bunch of other forms of damage which we don't have repair mechanisms for, because they affect us long after reproductive age.

The telomere issue is a common misconception when it comes to aging; it is at most a minor contributor, and if you want to live a really long time, lengthening the telomeres of your cells is probably the last thing you want to be doing.
While it's true that if you grab some cells from a person and culture them, then they will only be able to to undergo so many divisions as a result of telomere shortening, things are a little different inside the body. Basically all of our stem cells express telomerase, which means that they could in principle (were it not for other aspects of aging) divide an unlimited amount and renew our tissues indefinitely. So you will never die as a result of 'telomeres running out', because you will always have cells with telomerase active which are capable of producing however many cells are needed (though they can fail to do this properly, as a result of other aging mechanisms). For those somatic cells without telomerase, what usually happens when the telomeres run out is that the cell simply dies, and is replaced by the division of nearby cells - and this isn't harmful at all; we destroy and replace cells all the time. What is harmful, is those rare occasions in which the cell doesn't die. This leads to the cell becoming what is known as a 'senescent cell'. Not only do these cells not divide, but they also have several behaviours which are harmful to the organism. The senescent phenotype is thought to have arisen as an anti-cancer mechanism, to halt division in damaged cells that for whatever reason are unable to destroy themselves, and indeed most senescent cells are effectively "failed cancer cells" (cells suffering extensive DNA damage, or activation of oncogenes) rather than cells whose telomeres have run out. These cells have several behaviours which are designed to facilitate their destruction by the immune system; they secrete inflammatory cytokines, they secrete proteases (to break down the extracellular matrix so as to make it easier for immune cells to get to them) and they also secrete growth factors (to encourage the nearby cells to grow to replace the senescent cell once it has been destroyed). This is all fine so long as the immune system gets rid of them quickly, but often the immune system is unable to kill them (and it gets less effective with age). This means over time the number of senescent cells a person has will steadily increase. This is bad for the organism, because the senescent cell behaviours are harmful in the long run; the continual release of inflammatory cytokines leads to chronic inflammation, the proteases released weaken tissues (eg the thinning of the skin on older people is largely due to the presence of large numbers of senescent fibroblasts), and continual growth factor release (ironically) increases the risk of cancer by encouraging greater cell proliferation.

So in summary, telomere shortening does contribute to the production of senescent cells, but most senescent cells are produced by other mechanisms. So, although the idea of lengthening one's telomeres is a popular idea, it isn't something you'd really want to do if you were trying to treat aging because a) you wouldn't really reduce the number of senescent cells all that much and b) telomere shortening is actually a good thing, because it can stop cell lines that have become overly enthusiastic about replicating from becoming cancer cells. Instead the best way to deal with that problem would be to develop a way to selectively kill senescent cells.

Brilliant ! These are the sorts of answers I come here for, thanks Arcanyn

If anyone else had stuff to add, please do. I find this intriguing.

I don't think there is a "cause of death" per se, it is just that life stops.

Hehe, but then my question becomes what causes life to stop.

Well once you started looking at all the processes that go into keeping something alive then when these processes fail then death happens as just one possible side effect.

ramseyoptom wrote:IIRC there is one cell line used in cancer research which may be 100 years old and I think from a female.

You're thinking of Henrietta Lacks' cancer cells, Ramsey.

ramseyoptom wrote:Here, a problem I have often observed in the elderly, is that the gut no longer absorbs nutrients at the required levels. I have seen people in the local EMI Unit over the years just being 'cured' by having three square meals a day. This is the reason that supplements are often suggeted for the elderly in that a person may be getting the RDA but is not able to absorb efficiently and is thus not actually getting their RDA.

Not that I would call myself 'elderly', but I can attest to the deterioration of digestion as you get older. I have fairly recently lost the ability to digest milk products, wheat has become problematic if eaten in quantity, especially if it is refined, and on the whole I know that my digestion has slowed. I supplement, but how can I be assured that they will be absorbed any more than naturally occurring substances?

Great question Ciwan and great answers everyone, allow me to derail it slightly

Do you think that evolution is possible without death of the organism but the selection pressure being on an individual cell's ability to adapt to life as part of the organism?

I know there are a number of arguably immortal organisms but what I'm wondering is can complex life arise on a planet on which it's inhabitants have never known death? Can what happens in terms of natural selection on our planet happen as a microcosm in an organism?

Dawkins has a string matching example in Modeling Neural Networks with Mathematica by James Freeman, somewhere in the chapter on genetic algorithms... that code could be adapted to test the idea that death is a needed cog in the gears of evolution in a generalized way.

I think it is possible to have evolution without death provided that fitness sets the number of offspring. However, a population like that almost certainly meets evolutionary fitness goals more slowly than a population with death, and it might evolve very very slowly if mate selection had lottery style elements. And no doubt, modeling a horde of the undying unfit would be a serious resource drain on even a modern microprocessor compared to just clearing them.

To clarify: If there were a few superfit individuals, and they mate randomly in a unfit undying population, very few of their offspring would be improved compared to parents, and as a population, evolution likely equilibrates at a position far weaker than the one a system with death reaches.

Evolution is all about: fitness, sex and death. And just tiny pinch of mutation (far less than most people guess).

Thinking about the issue of evolution being able to proceed if individuals were effectively immortal, I would imagine that it would not generally be a problem. As even though individuals might be effectively immortal i.e. not degenerate from old age, under natural conditions they would be most likely to actually die in various other ways e.g. get eaten by something else. It would still be the fittest individuals that would generally survive long enough to reproduce, but in any population resources are not infinite, accidents and predation would still happen therefore evolution would still proceed and very few individuals would actually live forever. Ask yourself, how many animals actually get to die of old age anyway?

Of course proposing effectively immortal individuals is quite pointless, as while there are instances of a few, in general individuals will eventually die from lack of resources accidents or predation. Also as the OP stated evolution is blind to deleterious genes that do not express themselves until after reproductive age which therefore could be easily passed on, for what could be the mechanism that would prevent this from happening. Call them "death genes" if you want but I think that's a little dramatic.