Life span and evolution

Originally posted by apathist
A given life form fills a niche, usually. If they don't die off from old age then the niche is overrun and the species dies off.

If they don't die of old age, and often most or even all individuals of a species don't ever get the chance to die of old age because they often inevitably die of other causes anyway, that only means each individual would inevitably die from any one of the other causes of death, such as lack of food or room or from disease or predators etc. Thus their niche will not be 'overrun'.

Think of the example of an annual plant (or alternatively an animal) that cannot withstand the cold of winter as an adult and can only over-winter as seed (or, in the case of some annual animals such as some species of aphid, eggs) ; suppose they somehow all required a genetic trait that prevents them from ever dying of old age; they will still all die of the cold next winter so it would make no difference to the species and whether their niche would by 'overrun'.

So telemere caps are selected to be weak?
not because of the reason you imply.

Originally posted by Metal Brain
You are wrong.

https://realdoctorstu.com/2011/03/16/the-science-of-attraction-what-makes-a-beautiful-face/

How is that contrary to what I just said?
Natural selection would select for as to be attractive to an 'average' face where and when that maximizes the chances of reproductive success (of genes ) and natural selection would select against us to be attractive to an 'average' face where and when that maximizes the chances of reproductive success (of genes ) . In other words, the fundamental evolutionary driving force isn't whatever happens to be 'average' but rather what maximizes the chances of reproductive success.
If we are evolved to be attractive to an 'average' face then that is not because, with all else being equal (so no difference to the chances of reproductive success) , natural selection favors 'average', but rather there must be some kind of reproductive success advantage with us selecting 'average'. The only way you can show that I am wrong is to show evidence that 'average' was evolved when that 'average' actually works against chances of reproductive success.

Originally posted by humy
How is that contrary to what I just said?
Natural selection would select for as to be attractive to an 'average' face where and when that maximizes the chances of reproductive success (of genes ) and natural selection would select against us to be attractive to an 'average' face where and when that maximizes the chances of reproductive success (of genes ) . In ...[text shortened]... whatever happens to be 'average' but rather what maximizes the chances of reproductive success.

You said this:

"There is no evidence or reason to think that evolution favors, with all else being equal, 'average' traits in particular over those that aren't 'average'."

You are clearly wrong. Is your pride preventing you from being honest about it?

Originally posted by Metal Brain
You said this:

"There is no evidence or reason to think that evolution favors, with all else being equal, 'average' traits in particular over those that aren't 'average'."

Correct, and what you don't get is the operative words there are "with all else being equal" ; they are not i.e. not all else is equal in this case;
If we evolved to select an average face, that means there must be an increase chance of reproductive success by doing so because that is the way evolution works. And if there is an increase chance of reproductive success by doing so, then all else is NOT equal because there is a increase chance of reproductive success by doing so. Without that difference i.e. without an increase chance of reproductive success (of genes) , that selection of average wouldn't evolve. Comprehend?

As I just said in my last post;
"The only way you can show that I am wrong is to show evidence that 'average' was evolved when that 'average' actually works against chances of reproductive success." (of genes)

Originally posted by apathist
A given life form fills a niche, usually. If they don't die off from old age then the niche is overrun and the species dies off. So telemere caps are selected to be weak?

I don't think so. An individual within that niche that lives longer would (probably) breed more. Certainly, it would not breed less. How would evolution know that a species was going to be overrun at some future date by an unknown competitor?

So again, I don't think evolution played any deterministic role in an organisms lifespan. Over time within an ecological niche, evolution selects for traits with an increased fitness over your peers. If that trait requires a faster metabolism, then the chemical reactions in your body occur more quickly, your heart beats faster, and as a passive result of all those physical insults, you die sooner. If that trait slows the metabolism, then your body ages more slowly, and you live longer. Think of a rock in slow-moving river or a fast-moving one. Which one erodes first? The key experiment proving this is that calorie-restrictive diets result in slower metabolisms and prolonged aging.

Regarding incomplete DNA replication, it can be explained by biomechanics. The machinery that uses one DNA template to make a nearly identical copy is large and complex. When it is at the end of the template strand, not all of it can fit on the DNA strand and the machine falls apart. Bacteria solved the problem a long time ago with circular DNA but our DNA is much too large to make that work.

Originally posted by humy
If they don't die of old age, and often most or even all individuals of a species don't ever get the chance to die of old age because they often inevitably die of other causes anyway, that only means each individual would inevitably die from any one of the other causes of death, such as lack of food or room or from disease or predators etc. Thus their niche will not be 'overrun'.

Lack of food? Doesn't a limit on available food kinda describe a niche? And about disease and predators: how does dying early improve survival chances from them?

Think of the example of an annual plant (or alternatively an animal) that cannot withstand the cold of winter as an adult and can only over-winter as seed (or, in the case of some annual animals such as some species of aphid, eggs) ; suppose they somehow all required a genetic trait that prevents them from ever dying of old age; they will still all die of the cold next winter so it would make no difference to the species and whether their niche would by 'overrun'.
You have a point. But we know plants and bugs can survive winter. Through random mutation different survival strategies exist. Is it necessary that everything must die of old age (assuming they don't perish from other reasons first)? I thought that was the question.

So telemere caps are selected to be weak?
not because of the reason you imply.
So it is not possible that creatures with random mutations that cause stronger telemere caps die out from an overeating in their environmental niche? A stagnation since if they are successful, soon it's mostly older critters with no new genetic adaptions?

But telemeres are selected to be weak for some other reason?

Originally posted by apathist
[quote]Originally posted by humy
If they don't die of old age, and often most or even all individuals of a species don't ever get the chance to die of old age because they often inevitably die of other causes anyway, that only means each individual would inevitably die from any one of the other causes of death, such as lack of food or room or from ...[text shortened]... s with no new genetic adaptions?

But telemeres are selected to be weak for some other reason?

Lack of food? Doesn't a limit on available food kinda describe a niche?

Did I say/imply there isn't such thing as a niche?
I didn't.

And about disease and predators: how does dying early improve survival chances from them?

Where did I imply that it does?
I didn't.

Is it necessary that everything must die of old age (assuming they don't perish from other reasons first)?

Why would it be "necessary"?

So telemere caps are selected to be weak?
not because of the reason you imply.
So it is not possible that creatures with random mutations that cause stronger telemere caps die out from an overeating in their environmental niche?

Where did I imply this?

But telemeres are selected to be weak for some other reason?

yes, partial protection (unfortunately it isn't fool proof) from getting cancer. Natural selection will select for weaker telemeres up to reproductive age if that measurably increases the chances of reproductive success by measurably reducing the chances of dieing young before reproductive age. One harmful side effect of that is it contributes towards significantly shorter lifespan once your main window of opportunity for reproduction has come and passed but that still produces an overall NET increase chance of reproduction of your genes and, unfortunately, that is all what counts in evolution i.e evolution simply doesn't 'care' a less what happens to you after your opportunity for reproduction of your genes has passed.

There is evidence that telemeres function to come shorter so to prevent most mutated cells from dividing more than a certain number of times thus preventing most (unfortunately not all! It isn't fool proof hence there still sometimes exists cancer) of those mutated cells becoming deadly cancer cells.

https://en.wikipedia.org/wiki/Telomerase
"...Some experiments have raised questions on whether telomerase can be used as an anti-aging therapy, namely, the fact that mice with elevated levels of telomerase have higher cancer incidence and hence do not live longer. ..."

-and those mice on average do not live longer because they usually die of cancer before they have a chance to become very old let alone reproduce; THAT explains why we evolved with telomerase that become shorter; not to have a shorter life span because of aging but rather to on average have a longer life span so to, with all else being equal, give us a better chance to reproduce during our main opportunity to do so.

Originally posted by humy

...before they have a chance to become very old let alone reproduce; ....

missedit;
said that back-to-front and should have been;
" before they have a chance to reproduce let alone become very old ; ..."

Originally posted by humy...
-and those mice on average do not live longer because they usually die of cancer before they have a chance to become very old let alone reproduce; THAT explains why we evolved with telomerase that become shorter; not to have a shorter life span because of aging but rather to on average have a longer life span so to, with all else being equal, give us a better chance to reproduce during our main opportunity to do so.

Dying of old age would increase our chances of avoiding cancer, and so short telemeres are selected? Then why aren't we born dead?

Originally posted by apathist
Dying of old age would increase our chances of avoiding cancer

No, that is obviously nothing like what I said/implied/claimed/believe. Read my post again.

It is not the dying of old age that gives partial protection from cancer but shortening telemeres that gives partial protection from cancer but with a harmful side effect of increasing the chances of dying of old age but still with an average NET increase chance of reproductive success (of genes) hence natural selection selects for shortening telemeres despite that harm.

In other words, the reproduction advantage of the partial protection from cancer given by shortening telemeres more than compensates for the reproduction Disadvantage of the increase chance of dying of aging given by shortening telemeres hence it gives a net reproductive advantage hence natural selection selects for shortening telemeres.
This is because natural selection simply selects for whatever traits maximize average reproductive success of genes regardless of any other consequences of that, bad or good.

Exactly which part of that do you not comprehend?
I now lost count of the number of different ways I clearly explained that exact same thing to you and cannot see how it could be more obvious what I mean. I am sure everyone else here hasn't any difficulty understanding it; it really isn't complex or difficult to understand.

Originally posted by apathist
Dying of old age would increase our chances of avoiding cancer, and so short telemeres are selected? Then why aren't we born dead?

Telomeres act as a copy counter. They put a limit on how many times a cell line can reproduce. Cancer reproduces unusually fast. Putting a limit on the copy count therefore protects against cancer. Obviously there is a sweet spot where a smaller copy count would result in too early a death and a larger copy count would result in too much cancer. As with almost everything in evolution there are tradeoffs going on.

I have been identified as having a genetic mutation that interferes with the folic acid pathway. This may result in some bad side effects. But it also may have benefits, for example it probably confers some resistance to malaria (one of the most popular malaria prophylactics is an folic acid blocker).

Originally posted by humy...
It is not the dying of old age that gives partial protection from cancer but shortening telemeres that gives partial protection from cancer but with a harmful side effect of increasing the chances of dying of old age but still with an average NET increase chance of reproductive success (of genes) hence natural selection selects for shortening telemeres despite that harm. ...

I love you humy. I wonder what you see. Seems to me that living longer would spread the seed farther.

Originally posted by twhitehead
Telomeres act as a copy counter. They put a limit on how many times a cell line can reproduce. Cancer reproduces unusually fast. Putting a limit on the copy count therefore protects against cancer. Obviously there is a sweet spot where a smaller copy count would result in too early a death and a larger copy count would result in too much cancer. As with almo ...[text shortened]... some resistance to malaria (one of the most popular malaria prophylactics is an folic acid blocker).

Genes don't make decisions. You are saying we are programmed to die. But I'm drunk and probably wrong.

Originally posted by apathist
You are saying we are programmed to die. .

No, we are saying almost the opposite. We are evolved to live, not die, where and when that contributes to reproduction of genes. Sometimes weakening and death from aging is the occasional unfortunate side effect of this.

It may help you to understand evolution if you read the book "The selfish gene" by Richard Dawkins as, if my memory serves me correctly, that book more-or-less explains this.
(ANYONE; is that correct? It's a very long time since I have seen it)

Originally posted by apathist
Genes don't make decisions.

I don't think anyone in this thread doesn't know that.

You are saying we are programmed to die.
I said that it is plausible that cells are programmed to have a limited number of copies from birth as a cancer prevention mechanism (I have not studied this aspect of cells so cannot personally testify whether or not this is the case). This would result in eventual death as a side effect.

In a species where the leading cause of death is not old age, having an 'old age' mechanism does not have a very high cost. The issue is the relative cost of cancer vs the cost of old age. Evolution will find a balance between the two.