27 Dec 16
Originally posted by twhiteheadI agree that it is complicated. That is why I created this thread. I can usually come up with a decent theory to explain the course of evolution but this is the exception. I am assuming that life first evolved with unlimited life spans with the exception of predation and accidental killing.
Its a large topic that probably cannot be done full justice here. But ultimately it comes down to the most efficient way to reproduce in the niche that an organism is in.
1. It is essential that an organism reaches reproductive age, or assist in the reproduction of siblings or close relatives.
2. How long it lives after first reproductive age depends on ...[text shortened]... te for resources within the species vs those that mostly do not.
In summary, its complicated.
http://www.sciencefocus.com/article/nature/how-long-does-a-bacterium-live
Since some single celled organisms can have a very long life span I am trying to figure out why other multi-cellular species have evolved limited life spans. I started thinking that prey would have less need for a limited life span because of predation, but I do not think this is the case. Herbivores like cows do not live all that long so I had to abandon that theory.
I started to think that a limited life span might cause a species to evolve faster by eliminating the older individuals, but what about assexual reproduction? It isn't easy to make sense of this when all things are considered. Why not let an older individual live long and reproduce as long as that individual can survive in that environment? When I plant potatoes from tubers there is not much change in genetic material other than genetic drifting. Only if the potato sexually reproduces is there much genetic diversity in the gene pool.
The more I analyze this the more confused I get. That is why I am seeking help from others. I am curious.
There has to be some sort of competitive advantage to limited life spans. That is the only decent explanation I can think of, but I cannot come up with a comprehensive detailed explanation. Why does a rabbit grow old and die if it is likely to be eaten before it gets old?
27 Dec 16
2 edits
Originally posted by Metal BrainThat is a bad assumption to make. For single celled life forms, it is unreasonable to consider a cell line to be a single living thing. The actually living cells typically do not live that long. There are exceptions, but it is not the rule. With single celled life forms there is definitely a competitive advantage to being able to reproduce fast and evolve fast.
I am assuming that life first evolved with unlimited life spans....
Only if the potato sexually reproduces is there much genetic diversity in the gene pool.
Plants are a completely different case from animals. Many plants are annual simply because surviving the winter or one particular season can be a problem. They put all their effort into reproducing for the year.
Plants that are not annual often do not have set age limits and do not grow old as such. Most plants do have the problem that they keep growing and that usually sets a limit.
Why does a rabbit grow old and die if it is likely to be eaten before it gets old?
Part of the problem is simply that there is no selection for things to help it survive old age. Most ageing is not so much programmed ageing but lack of programmed anti-ageing.
Also very important with animals is the fact that they are typically programmed to grow to a certain size and no more. In many cases this result in shutting down the growing which to some extent shuts down the repair. Even when repair is active there is a delicate balance between repairing too fast which become growth, and not enough repair. It is notable that animals that are able to keep growing tend to live unusually long lives compared to those that do not.
27 Dec 16
Originally posted by twhitehead"Most ageing is not so much programmed ageing but lack of programmed anti-ageing."
That is a bad assumption to make. For single celled life forms, it is unreasonable to consider a cell line to be a single living thing. The actually living cells typically do not live that long. There are exceptions, but it is not the rule. With single celled life forms there is definitely a competitive advantage to being able to reproduce fast and evolve ...[text shortened]... s that are able to keep growing tend to live unusually long lives compared to those that do not.
I am skeptical of that claim. What is your source of information?
27 Dec 16
Have a look at the topic of cell death, for example at:
https://en.wikipedia.org/wiki/Apoptosis
There appears to be a chemical or molecular-level process going on all the time to 'age out' cells. This may be relevant to the question what the life span of any given species is.
Generally, speaking, the more complicated the organism, the more possible ways cell regeneration can go wrong.
Furthermore, a species which lives in a very stable environment can be expected to become very well-adapted to it over time and thereby lose the capacity to adapt to other environments, whereas species which live in unstable environments, or which move around a lot, tend to retain the capacity to adapt to change. Adapting to change is complicated, staying the same is simple.
Empirical evidence to date indicates that some of the longest-lived organisms are also some of the simplest and thrive in extremely stable regions. See for example:
https://www.washingtonpost.com/news/speaking-of-science/wp/2016/05/26/a-sea-sponge-the-size-of-a-minivan-could-be-one-of-the-worlds-oldest-living-animals/
27 Dec 16
1 edit
Originally posted by moonbusThis is a great topic. I think it is important, however, to distinguish between cellular mechanisms of aging and organismal mechanisms. It is a cell, not an organism, that undergoes apoptosis (more appropriately termed "senescence" in the context of aging). This mechanism relates to the very imprecise task of maintaining the ends of linear chromosomes during DNA replication. Over each cell division, a piece of the chromosome is lost. In gametes, this length is maintained by an enzyme not typically present in somatic cells. And in fact, at the cellular level, just a few changes can overcome mortality.
Have a look at the topic of cell death, for example at:
https://en.wikipedia.org/wiki/Apoptosis
There appears to be a chemical or molecular-level process going on all the time to 'age out' cells. This may be relevant to the question what the life span of any given species is.
Generally, speaking, the more complicated the organism, the more possible ...[text shortened]... /2016/05/26/a-sea-sponge-the-size-of-a-minivan-could-be-one-of-the-worlds-oldest-living-animals/
But organisms operate differently. To keep things in balance, multi-celled organisms have evolved very precise mechanisms for keeping cell division under control, during development and homeostasis. Thus, cells are born to die to benefit the organism. Many cancer-causing mutations occur in genes that are involved in the negative regulation of cell division.
27 Dec 16
1 edit
Originally posted by wildgrassThe point is that cellular death and regeneration cannot continue indefinitely (in an individual); an organism eventually succumbs to an imbalance between cellular deaths and regeneration whereby the cellular deaths overtake the organism's capacity to regenerate.
This is a great topic. I think it is important, however, to distinguish between cellular mechanisms of aging and organismal mechanisms. It is a cell, not an organism, that undergoes apoptosis (more appropriately termed "senescence" in the context of aging). This mechanism relates to the very imprecise task of maintaining the ends of linear chromosomes duri ...[text shortened]... -causing mutations occur in genes that are involved in the negative regulation of cell division.
Moreover, some types of cells do not regenerate, e.g., brains in mammals.
27 Dec 16
Originally posted by Metal BrainMy somewhat inadequate knowledge of the subject. I could be wrong. I also suspect that it is more complicated than one or the other but a complex interplay of many things with differences depending on which particular cell type or organism we are talking about.
"Most ageing is not so much programmed ageing but lack of programmed anti-ageing."
I am skeptical of that claim. What is your source of information?
28 Dec 16
Originally posted by moonbusYes. Lifespans are generally inversely correlated with metabolic rates. Calorie restrictive diets (even in mammals), which lower metabolic rates, can dramatically prolong lifespan. Animals whose niche require a high metabolism (i.e. foragers, frequent feeders) tend to have shorter lifespans. This is attributed to chemical forces acting on the stem cells and organism which, as you say, cannot keep up with the necessary repairs.
The point is that cellular death and regeneration cannot continue indefinitely (in an individual); an organism eventually succumbs to an imbalance between cellular deaths and regeneration whereby the cellular deaths overtake the organism's capacity to regenerate.
Moreover, some types of cells do not regenerate, e.g., brains in mammals.
An organism is not just cells, either. A heart valve, for instance, undergoes constant extracellular remodeling to maintain its integrity and function. Faster heart beats require more remodeling in a given time.
29 Dec 16
Originally posted by wildgrassI agree: at every level, molecular, cellular, single organ, and whole organism--there are factors which limit age. For example, organs which filter blood tend to accumulate toxins (pesticides, heavy metals, and so on) which ultimately degrade the organism's ability to regenerate. Blood vessels accumulate plaque and fatty deposits; nerve sheaths degenerate, etc. etc.
Yes. Lifespans are generally inversely correlated with metabolic rates. Calorie restrictive diets (even in mammals), which lower metabolic rates, can dramatically prolong lifespan. Animals whose niche require a high metabolism (i.e. foragers, frequent feeders) tend to have shorter lifespans. This is attributed to chemical forces acting on the stem cells an ...[text shortened]... maintain its integrity and function. Faster heart beats require more remodeling in a given time.
29 Dec 16
Originally posted by moonbusIt has been proven that selective breeding can lengthen the life span of fruit flies.
Have a look at the topic of cell death, for example at:
https://en.wikipedia.org/wiki/Apoptosis
There appears to be a chemical or molecular-level process going on all the time to 'age out' cells. This may be relevant to the question what the life span of any given species is.
Generally, speaking, the more complicated the organism, the more possible ...[text shortened]... /2016/05/26/a-sea-sponge-the-size-of-a-minivan-could-be-one-of-the-worlds-oldest-living-animals/
http://www.nytimes.com/2005/12/06/science/live-longer-with-evolution-evidence-may-lie-in-fruit-flies.html?_r=0
The opposite has been done unintentionally by dog breeding. They have shorter life spans than wolves.
http://www.huffingtonpost.com/quora/why-do-dogs-have-such-sho_b_6083772.html
I think it is possible to selectively breed mammals to have a longer life span including people. The only question as far as I am concerned is how much. For this reason I am still skeptical that life first evolved with a limited life span. I could be wrong, but I do not think so. Single celled species can have long life spans.
29 Dec 16
Originally posted by Metal BrainThere is some evidence that human lifespans can be genetic (although complicated by lifestyle factors, see the island of Sardinia, Italy http://www.ibtimes.com/sardinias-secret-longevity-genetics-diet-lifestyle-754380).
It has been proven that selective breeding can lengthen the life span of fruit flies.
http://www.nytimes.com/2005/12/06/science/live-longer-with-evolution-evidence-may-lie-in-fruit-flies.html?_r=0
The opposite has been done unintentionally by dog breeding. They have shorter life spans than wolves.
http://www.huffingtonpost.com/quora/why-do-dogs- ...[text shortened]... e span. I could be wrong, but I do not think so. Single celled species can have long life spans.
Also, I would not rely on domesticated species for evidence of evolutionary oddities. These species did not evolve by "survival of the fittest" as they say.
The metabolic rate theory makes the most sense to me to explain species-specific aging. There's an article here: http://www.discoverymedicine.com/S-J-Olshansky/2009/07/25/what-determines-longevity-metabolic-rate-or-stability/
Cells (and organisms) are essentially a controlled series of very high-energy chemical reactions, that receives constant bombardment from free radicals and external forces. So I don't think it makes sense to think of a cell (or organism) as fundamentally immortal, as it is subject to enormous physical degradation. Evolutionarily, an animal should reproduce as quickly and as much as possible before these physical forces limit its fitness (at which point it should die and stop consuming resources.)
30 Dec 16
12 edits
Originally posted by Metal Brainliving things being programmed to age specifically to function to die of aging, unless this (somehow) results in an overall reproductive advantage (and I/we don't see how), wouldn't make any evolutionary sense whatsoever i.e. cannot be explained by evolution theory. Thus your skeptical of that claim is irrational and/or based on ignorance of the subject.
"Most ageing is not so much programmed ageing but lack of programmed anti-ageing."
I am skeptical of that claim. What is your source of information?
"lack of programmed anti-ageing" in contrast can be relatively easily be explained with evolution theory; there is often a vanishingly small reproductive advantage to living much beyond your main reproductive window of opportunity thus there is often no measurable natural selection pressure for anti-aging attributes for beyond that window.
30 Dec 16
Originally posted by humy... there is often a vanishingly small reproductive advantage to living much beyond your main reproductive window of opportunity ...So why is there often this 'small window'? You say we aren't 'programmed' to die; instead we just aren't programmed to not die, because we can reproduce only for a short time. But why is the window so small? Why is wrong to suggest the window size is programmed?
I already know I'm stupid, so don't bother pointing that out. Unless you want to behave like a pompous jerk.
30 Dec 16
13 edits
Originally posted by apathistI didn't say it was 'small'; try the word 'finite'.
So why is there often this 'small window'?
This window is finite in length (usually with fuzzy ill-defined boundaries ) for all sorts of reasons and depending on the species. For example, for some annual plants that only over-winter as seed, the adult plants will be killed by frost if nothing else by the next coming winter long before they get any second chance to reproduce, say, a year later. This would explain why evolution wouldn't give them the genetic attributes to prevent them from deteriorating with relatively 'long' age (beyond one year in this case) if they were hypothetically not ever exposed to the lethal cold of winter.
If there once was a stone-age man with some mutations that would stop him deteriorating with relatively 'long' age (say, 1000 years old ) if he had hypothetically not died of any other natural causes, he would probably would have still died before he was 50 years old anyway from any one of the many common other natural causes so natural selection would have been unlikely to have selected those mutations in favor over those mutations that help the person more before they have a chance to be 50 years old.
You say we aren't 'programmed' to die; instead we just aren't programmed to not die, because we can reproduce only for a short time.
Not exactly; just replace the word "short" there with "finite" and I think you then have just about got what I am saying.
Note I do not imply there must always be a well defined exact end-boundary point in time to when that window of opportunity ceases; usually there isn't.