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Evolution and death
Please only answer the following if you believe in evolution and please also do not reply with religious explanations (in both cases, to avoid spurious sub discussions)
Why does death exist given our current knowledge of evolution?
It could be argued that there is no need for death, because competition would result is culling of the weak and old and so it is not necessary for evolution.
Social arguments against competition by offspring are invalid, because all forms of life ie bacteria, seem to have death built into their DNA.
I am loathe to accept the fact that the constant copying of cells leads to degradation, because if this was the reason, most lifeforms would have the same lifespan in the absence of competition.
I am loathe to accept the argument of competition, because life-forms could be kept alive indefinitely in a perfect environment. (In the absence of any competition)
Is death a hangover of some basic property of life that has been propagated from it's inception, or is there another more obvious explanation given current evolutionary theory
Why does death exist given our current knowledge of evolution?
It could be argued that there is no need for death, because competition would result is culling of the weak and old and so it is not necessary for evolution.
Social arguments against competition by offspring are invalid, because all forms of life ie bacteria, seem to have death built into their DNA.
I am loathe to accept the fact that the constant copying of cells leads to degradation, because if this was the reason, most lifeforms would have the same lifespan in the absence of competition.
I am loathe to accept the argument of competition, because life-forms could be kept alive indefinitely in a perfect environment. (In the absence of any competition)
Is death a hangover of some basic property of life that has been propagated from it's inception, or is there another more obvious explanation given current evolutionary theory
Answers
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As rov1200 said, we are not built to be everlasting.
You mention that competition would result in the culling of the weak and the old .. presumably by them either dying or being killed off in some other way. Whatever the mechanism, the end result is the same - they die.
And there is one very simple practical reason too ... if we didn't die off the world would get rather crowded, and overall we can only support and feed a (large but) limited number of people. Or do you envisage us eveolving to the point where we don't need to eat ?
You mention that competition would result in the culling of the weak and the old .. presumably by them either dying or being killed off in some other way. Whatever the mechanism, the end result is the same - they die.
And there is one very simple practical reason too ... if we didn't die off the world would get rather crowded, and overall we can only support and feed a (large but) limited number of people. Or do you envisage us eveolving to the point where we don't need to eat ?
No those are bad answers
They do not explain why we cannot continue to repair our bodies, why we wear out, they just observe that we do.
Death is the price we pay for sex.
Before sexual reproduction you have amoeba and the like. When they split you have two perfect copies.
Which is the parent and which is the child?
The question makes no sense so in a way amoeba are immortal.
Imagine a planet devoid of animal life.
In which there are 3 Animal species A reproduces asexually, B sexually and does not age and C sexually but does age and die.
After a few generations A has the least variation, B has more variation and C the most variation.
B has more variation than C because the original generation competes with the later generations so fewer of the later generations get enough resources and get to reproduce.
Now the environment changes - rapidly!
The species with the most variation is in the best position to survive the rapid change - or at least some of them are.
So the question is actually rather the reverse - why are there still asexually reproducing creatures.
I would suggest that if you look at creatures like bacteria they evolved to become very, very hardy.
I may be way off, I'm not a biologist and these are just my thoughts.
Very good question though
They do not explain why we cannot continue to repair our bodies, why we wear out, they just observe that we do.
Death is the price we pay for sex.
Before sexual reproduction you have amoeba and the like. When they split you have two perfect copies.
Which is the parent and which is the child?
The question makes no sense so in a way amoeba are immortal.
Imagine a planet devoid of animal life.
In which there are 3 Animal species A reproduces asexually, B sexually and does not age and C sexually but does age and die.
After a few generations A has the least variation, B has more variation and C the most variation.
B has more variation than C because the original generation competes with the later generations so fewer of the later generations get enough resources and get to reproduce.
Now the environment changes - rapidly!
The species with the most variation is in the best position to survive the rapid change - or at least some of them are.
So the question is actually rather the reverse - why are there still asexually reproducing creatures.
I would suggest that if you look at creatures like bacteria they evolved to become very, very hardy.
I may be way off, I'm not a biologist and these are just my thoughts.
Very good question though
Why would just copying aging lead to all creatures having similar lifespans. Different animals have different cell structures arranged in different ways doing different jobs.
Examples of unique cell structure is shown by specific diseases like rabies that can only affect specific mammals. If cell degradation was all the same then cells would all be the same and we could all get the same diseases.
Plus our brains are much more complex than other animals so there are more things to go wrong, extrapolate a similar argument to all organs and ultimately cells in the body and simple degradation of copies gives death.
Plus some cells stop or never start regenerating after birth, leading to death.
Plus enviromental factors and random chance give rise to problems in cell copying, worst case developing cancer or other problems leading to death. Live long enough and some cells will mutate in a malignant way. The more cells and more complex the DNA the greater the odds of dangerous mutation in a given period.
Plus simple accidents will always kill things.
Loads of reasons for death, and your question has one very strange statement "there is no need for death". Who says death needs a reason?
Examples of unique cell structure is shown by specific diseases like rabies that can only affect specific mammals. If cell degradation was all the same then cells would all be the same and we could all get the same diseases.
Plus our brains are much more complex than other animals so there are more things to go wrong, extrapolate a similar argument to all organs and ultimately cells in the body and simple degradation of copies gives death.
Plus some cells stop or never start regenerating after birth, leading to death.
Plus enviromental factors and random chance give rise to problems in cell copying, worst case developing cancer or other problems leading to death. Live long enough and some cells will mutate in a malignant way. The more cells and more complex the DNA the greater the odds of dangerous mutation in a given period.
Plus simple accidents will always kill things.
Loads of reasons for death, and your question has one very strange statement "there is no need for death". Who says death needs a reason?
Jake, there are still asexually reproducing creatures because they do still evolve, through mutations in the DNA just like mutations within cells in more complex organisms. Asexually reproducing organisms are the most prolific and varied organsims on the planet, they have the, most variationa nd can change the quickest because there isnt much to change, just one cell.
Single celled organisms tend to inhabit very small specific ecosystems with very fine tolerances. If their environment changes a tiny bit they die, but luckily for them the ecosystem is so small that it is actually very robust. i.e. they require a very specific level of something very specific, like CO or a pH level, seems fragile but the upside is that they don't care about anything else. On the other hand more complex multi-cellular creatures need clean water, sufficient oxygen, low levels of toxins, the right amount and right type of nutrition, all very variable and also susceptible to the same problems. We depend on more factors so perversely we are less adaptable to major changes but more adaptable to minor changes.
Single celled organisms tend to inhabit very small specific ecosystems with very fine tolerances. If their environment changes a tiny bit they die, but luckily for them the ecosystem is so small that it is actually very robust. i.e. they require a very specific level of something very specific, like CO or a pH level, seems fragile but the upside is that they don't care about anything else. On the other hand more complex multi-cellular creatures need clean water, sufficient oxygen, low levels of toxins, the right amount and right type of nutrition, all very variable and also susceptible to the same problems. We depend on more factors so perversely we are less adaptable to major changes but more adaptable to minor changes.
Symmetrygirl
I fully understand that asexually reproducing creatures do evolve through mutations. You see similar mutation in our own mitacondria
My question is why have they not been outcompeted by sexually reproducing creatures.
Your answer about depending on small numbers of factors is interesting but you do not relate that to asexual reproduction - you simply observe that asexually reproducing creatures such as bacteria tend to inhabit such niches without explaining why that should be so
I fully understand that asexually reproducing creatures do evolve through mutations. You see similar mutation in our own mitacondria
My question is why have they not been outcompeted by sexually reproducing creatures.
Your answer about depending on small numbers of factors is interesting but you do not relate that to asexual reproduction - you simply observe that asexually reproducing creatures such as bacteria tend to inhabit such niches without explaining why that should be so
Every organism only has a finite amount of resources (energy from food etc.). Whilst it might be possible for an organism to develop hugely efficient immune and regeneration systems, these developments would have to be at the cost of something else, such as the investment of energy into the production and (if applicable) rearing of offspring. Since natural selection favours traits whihc increase reproduction (abilities to avoid predators or attract more mates), there is a trade-off between longer life and maximisign reprosuctiove sucess.
The exact nature of this trade-off is different for different organisms with different life histories - those which are likely to die younger, or are subject to more competition for mating/reproductive opportunities will devote more energy into maximising the number of offspring they have whilst they can and have a correspondingly less well-developed immune system.
The exact nature of this trade-off is different for different organisms with different life histories - those which are likely to die younger, or are subject to more competition for mating/reproductive opportunities will devote more energy into maximising the number of offspring they have whilst they can and have a correspondingly less well-developed immune system.
(apologies for previous typos)
I should probably add a little explaning why immune systems and repair are necessary and why it isn't possible to keep organisms alive indefinately.
At the level of the whole animal, tissues and organs succumb to wear and tear - parts eventually wear out and are not repaired for the reasons I mentioned in my last past (concerning allocation of resources).
At the cellular/ molecular level, the chemical constituents of our cells are subject to damaging chemical reactions (oxygen, water etc.). Such damage is patched up and repaired as necessary and is one of the key roles of our immune systems. However, such a system is not perfect due to the inherent life history trade-offs and organisms cannot continue to function at top rate.
Added to these effects is the presence of pathogens (such as bacteria, viruses and various parasites) and predators (or herbivores in the case of plants). In other words, its a tough old world!
I should probably add a little explaning why immune systems and repair are necessary and why it isn't possible to keep organisms alive indefinately.
At the level of the whole animal, tissues and organs succumb to wear and tear - parts eventually wear out and are not repaired for the reasons I mentioned in my last past (concerning allocation of resources).
At the cellular/ molecular level, the chemical constituents of our cells are subject to damaging chemical reactions (oxygen, water etc.). Such damage is patched up and repaired as necessary and is one of the key roles of our immune systems. However, such a system is not perfect due to the inherent life history trade-offs and organisms cannot continue to function at top rate.
Added to these effects is the presence of pathogens (such as bacteria, viruses and various parasites) and predators (or herbivores in the case of plants). In other words, its a tough old world!
Single celled creatures inhabit such niches because they are able to and not much else is. Simplicity gives the ability to survive extreme conditions and if nothing else can compete then these creatures will continue to survive and thrive. If they do this they do not need to change or adapt anymore.
Complex creatures would do it if they could and actually do to a certain extent, deep sea fish can only live very deep down too shallow and they die, but at their depth there is less competition. Those shrimp that live on the edge of volcanic vents are another example. Freshwater crocs and saltwater crocs live in different environments and so avoid competition with each other. Bacteria can just do it to a greater extent.
Complex creatures would do it if they could and actually do to a certain extent, deep sea fish can only live very deep down too shallow and they die, but at their depth there is less competition. Those shrimp that live on the edge of volcanic vents are another example. Freshwater crocs and saltwater crocs live in different environments and so avoid competition with each other. Bacteria can just do it to a greater extent.
Asexual reproduction means the exact DNA is passed on not a random mix as in sexual reproduction so the offspring will have exactly the same characteristics and be able to survive in the same conditions. Plus asexual reproduction requires less energy and resources (no genitals for one thing) so asexual reproduction necessarily means less complexity and less strain on resources, and vice versa. As discussed less complexity means more adaptability and a greater capacity for variability and more success in life and reproduction.
It is not that asexual creatures have these traits that is significant, it is that sexually reproducing creatures cant have these traits. If they could they would in accordance with evolutionary theory.
It is not that asexual creatures have these traits that is significant, it is that sexually reproducing creatures cant have these traits. If they could they would in accordance with evolutionary theory.
My question relates to why natural aging has come about and whether it relates to evolutionary theory.
I posted this question on other notice boards and think that �Death is the price we pay for sex� provides many answers �
1. Genes have evolved to maximise reproduction, not through any purpose, but solely because that reproduction ensures that the gene continues to exist.
2. The environment has imposed genetic constraints on lifespan because cells of any kind,( animal or vegetable) cannot reproduce endlessly and so reproduction lifespan within genes has been built to match the respective environment.
3. There is a physical limit within the DNA copying process and if this could somehow miraculously be removed, then organisms would continue to reproduce until competition for resources made that organism no longer suitable for its environment or it died in competition for resources.
I want to simulate evolution in a computer environment and so need to know if death by natural aging is vital to evolution.
I do not think this is the case, because death by natural aging appears to be caused by the degradation in the physical copying of DNA, which does not occur in digital systems.
Regarding sexual versus asexual reproduction �
Asexual reproduction is obviously successful within given environments because it exists today (and is exceptionally successful because of the prevalence of asexual organisms), so my next question would to be ask why this is a useful evolutionary strategy. (Re Jake - reproduce like crazy, but get zapped by competition in the current environment but in that reproductive frenzy, rely on mutational changes in DNA to create an organism that can survive in the current environment)
If you have any further thoughts then please expand on why life forms die of old age
Willo89
I posted this question on other notice boards and think that �Death is the price we pay for sex� provides many answers �
1. Genes have evolved to maximise reproduction, not through any purpose, but solely because that reproduction ensures that the gene continues to exist.
2. The environment has imposed genetic constraints on lifespan because cells of any kind,( animal or vegetable) cannot reproduce endlessly and so reproduction lifespan within genes has been built to match the respective environment.
3. There is a physical limit within the DNA copying process and if this could somehow miraculously be removed, then organisms would continue to reproduce until competition for resources made that organism no longer suitable for its environment or it died in competition for resources.
I want to simulate evolution in a computer environment and so need to know if death by natural aging is vital to evolution.
I do not think this is the case, because death by natural aging appears to be caused by the degradation in the physical copying of DNA, which does not occur in digital systems.
Regarding sexual versus asexual reproduction �
Asexual reproduction is obviously successful within given environments because it exists today (and is exceptionally successful because of the prevalence of asexual organisms), so my next question would to be ask why this is a useful evolutionary strategy. (Re Jake - reproduce like crazy, but get zapped by competition in the current environment but in that reproductive frenzy, rely on mutational changes in DNA to create an organism that can survive in the current environment)
If you have any further thoughts then please expand on why life forms die of old age
Willo89
It is more remarkable that sexual reproduction is so prevalent. Sexual reproduction is costly: Consider two populations of equal size, one reproducing sexually, one asexually, and females each produce 2 offspring.
In the asexual population, every member of the new generation is capable of producing 2 further offspring and the population can double in each generation, whereas in the sexual population, only 50% of the new generation (the females) can reproduce and the population does not increase.
The costliness of males (the two-fold cost of sex, http://en.wikipedia.org/wiki/Two-fold_cost_of_ sex) was first described by John Maynard Smith.
In order to explain the evolution of sexual reproduction, we must explain how a strategy in which only one half of the population (assuming a 50:50 sex ratio) can reproduce, can ever be successful. Most answers relate to the ability of sexual reproduction to create novel genotypes more quickly and to increase the spread of advantageous traits.
In the asexual population, every member of the new generation is capable of producing 2 further offspring and the population can double in each generation, whereas in the sexual population, only 50% of the new generation (the females) can reproduce and the population does not increase.
The costliness of males (the two-fold cost of sex, http://en.wikipedia.org/wiki/Two-fold_cost_of_ sex) was first described by John Maynard Smith.
In order to explain the evolution of sexual reproduction, we must explain how a strategy in which only one half of the population (assuming a 50:50 sex ratio) can reproduce, can ever be successful. Most answers relate to the ability of sexual reproduction to create novel genotypes more quickly and to increase the spread of advantageous traits.
I'm afraid the simulation will have to include a random factor regarding the degradation of the DNA. Although it would have to include a level of random mutation anyway to enable modelling of a beneficent mutation, so the simulation just has to include a time-dependent level of mutation within organisms that eventually kills them.
A decay constant related to the genetic structure and a condition where a smaller decay constant leads to a better chance of reproducing should model the evolutionary advantage of living longer. Just have to find a way to limit the minimum size by including negative aspects of old age somewhere (e.g.more resources consumed, more likely to be killed in competition etc.). A tricky simulation
A decay constant related to the genetic structure and a condition where a smaller decay constant leads to a better chance of reproducing should model the evolutionary advantage of living longer. Just have to find a way to limit the minimum size by including negative aspects of old age somewhere (e.g.more resources consumed, more likely to be killed in competition etc.). A tricky simulation
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