Ageing: The girls who never grow older • Hacker News Board

Re: Ageing: The girls who never grow older

#21

Post by deciplex » Wed, May 21, 2014, 5:17 AM UTC

crystaln wrote: post #16

jostmey wrote: post #14

Earlier quoted context omitted.

First of all, there are a number of things that go wrong in our bodies as we age. Certainly genetic errors build up over time and are left uncorrected. But this is just one of many things that go wrong. The reason our bodies are allowed to degrade in the first place is because we have usually already survived well into our reproductive age. The evolutionary theories of aging actually provide a pretty solid explanatio…

Would it not make more evolutionary sense to remain reproductively capable for hundreds or thousands of years? The motive for genes to reproduce does not end after a single set of offspring. In fact, I don't think the motivation is even reduced.

Think about it from the perspective of genetic material temporarily 'trapped' in the body like passengers on a boat. All else being equal, a new boat is better than an old boat. And, a new body is better than an old body (even if all the error correction machinery is there and fully working, a 26 year-old body has an advantage over a 46 year-old one, or an 86 year-old one). After the genetic material has been transferred to a new body, via reproduction, i.e. the passengers have been transferred to the new boat, what purpose does the old boat serve other than to consume resources that could be used by the new one?

I think there is a case to be made that death gives organisms, that is to say it gives genetic material (which is the important bit, not the organism which is a mere vessel for the genes) an evolutionary advantage.

Re: Ageing: The girls who never grow older

#22

Post by [deleted] » Wed, May 21, 2014, 5:22 AM UTC

jostmey wrote: post #17

crystaln wrote: post #16

Earlier quoted context omitted.

Would it not make more evolutionary sense to remain reproductively capable for hundreds or thousands of years? The motive for genes to reproduce does not end after a single set of offspring. In fact, I don't think the motivation is even reduced.

The mathematics of life is exponential growth. Two begets four begets eight and so on. So if you happen to die from old age after the fifth or sixth generation, the effect on how many copies your genes make of themselves is marginal.

[deleted]

Re: Ageing: The girls who never grow older

#23

Post by thaumasiotes » Wed, May 21, 2014, 5:22 AM UTC

jostmey wrote: post #17

crystaln wrote: post #16

Earlier quoted context omitted.

Would it not make more evolutionary sense to remain reproductively capable for hundreds or thousands of years? The motive for genes to reproduce does not end after a single set of offspring. In fact, I don't think the motivation is even reduced.

The mathematics of life is exponential growth. Two begets four begets eight and so on. So if you happen to die from old age after the fifth or sixth generation, the effect on how many copies your genes make of themselves is marginal.

But that's total nonsense. Taking the model you describe, where everyone has two children, look at two scenarios:

1. You, and only you, have a magically extended life, such that if you choose you can reproduce at any point.

In scenario (1), every generation after you represents one copy of your genes. When you have a third child in the fifth generation, the world goes from one additional copy of you to 1.5 copies, a 50% increase.

2. You, and all of your descendants, never die.

In scenario (2), every generation after you is still one full copy of your genes, but they add up over time because they never die. When you have an extra child in the fifth generation, the number of copies of your genes (again, not counting you) goes from 5 to 5.5, a 10% increase. That's still hugely significant.

Let's imagine a third scenario:

3. Your genes are so massively successful that people in your family line have three children, not two children. But except for you, they die like normal.

In scenario (3), after 5 generations your 243 generation-5 descendants represent 7.6 copies of your genes. An extra child at this point would increase your representation to 8.1, a 6.6% increase.

The mistake you appear to be making is in not realizing that the exponential increase in your descendants is offset by an exponential decay in how related they are to you. Another child, at any point, is hugely valuable, because your child is 16 times more strongly related to you than your great-great-great-grandchild.

Re: Ageing: The girls who never grow older

#24

Post by jostmey » Wed, May 21, 2014, 5:34 AM UTC

ars wrote: post #20

jostmey wrote: post #17

Earlier quoted context omitted.

The mathematics of life is exponential growth. Two begets four begets eight and so on. So if you happen to die from old age after the fifth or sixth generation, the effect on how many copies your genes make of themselves is marginal.

You are completely forgetting that if the parent organism has extra copies so do all the children. Compare 2^100 vs 3^100: 2^100: 1267650600228229401496703205376 3^100: 515377520732011331036461129765621272702107522001

No, I am not. I assumed that the offspring will die of old age too.

You neglected the variable of time. That third offspring will be born after the second one, which is born after the first one. You need to use the Euler-Lotka equation. The mathematics was worked out centuries ago. Here is the wikipedia article

http://en.wikipedia.org/wiki/Euler%E2%80%93Lotka_equation

Re: Ageing: The girls who never grow older

#25

Post by hrjet » Wed, May 21, 2014, 5:50 AM UTC

crystaln wrote: post #16

jostmey wrote: post #14

Earlier quoted context omitted.

First of all, there are a number of things that go wrong in our bodies as we age. Certainly genetic errors build up over time and are left uncorrected. But this is just one of many things that go wrong. The reason our bodies are allowed to degrade in the first place is because we have usually already survived well into our reproductive age. The evolutionary theories of aging actually provide a pretty solid explanatio…

Would it not make more evolutionary sense to remain reproductively capable for hundreds or thousands of years? The motive for genes to reproduce does not end after a single set of offspring. In fact, I don't think the motivation is even reduced.

A large life-span would starve the younger generations of resources. And the younger generations are probably more crucial to the survival of the gene pool, than the older generations for various reasons. One reason is that younger generations might be better adapted to the environment because of mutations.

Another reason could be that the brains and bodies of older generations will eventually get saturated / tired. Keeping them alive is inefficient for the species.

Re: Ageing: The girls who never grow older

#26

Post by sixQuarks » Wed, May 21, 2014, 5:52 AM UTC

Does anyone have pictures of these girls? I'm curious to see what they actually look like.

Re: Ageing: The girls who never grow older

#27

Post by ars » Wed, May 21, 2014, 5:59 AM UTC

jostmey wrote: post #24

ars wrote: post #20

Earlier quoted context omitted.

You are completely forgetting that if the parent organism has extra copies so do all the children. Compare 2^100 vs 3^100: 2^100: 1267650600228229401496703205376 3^100: 515377520732011331036461129765621272702107522001

No, I am not. I assumed that the offspring will die of old age too. You neglected the variable of time. That third offspring will be born after the second one, which is born after the first one. You need to use the Euler-Lotka equation. The mathematics was worked out centuries ago. Here is the wikipedia article http://en.wikipedia.org/wiki/Euler%E2%80%93Lotka_equation

> No, I am not. I assumed that the offspring will die of old age too.

How does that change the conclusion? 3 children vs 2 is still immensely more children, not just a marginal amount as you thought.

Re: Ageing: The girls who never grow older

#28

Post by jostmey » Wed, May 21, 2014, 6:13 AM UTC

ars wrote: post #27

jostmey wrote: post #24

Earlier quoted context omitted.

No, I am not. I assumed that the offspring will die of old age too. You neglected the variable of time. That third offspring will be born after the second one, which is born after the first one. You need to use the Euler-Lotka equation. The mathematics was worked out centuries ago. Here is the wikipedia article http://en.wikipedia.org/wiki/Euler%E2%80%93Lotka_equation

> No, I am not. I assumed that the offspring will die of old age too. How does that change the conclusion? 3 children vs 2 is still immensely more children, not just a marginal amount as you thought.

When that third child is being born the second child is already beginning to reproduce (if you reproduce like Yeast). Clearly, that second child is more important because it has already given you a grandchild when your third child is still in the process of being born. That second child has already resulted into two offspring, and counts for twice as much.

Re: Ageing: The girls who never grow older

#29

Post by zorpner » Wed, May 21, 2014, 6:33 AM UTC

crystaln wrote: post #16

jostmey wrote: post #14

Earlier quoted context omitted.

First of all, there are a number of things that go wrong in our bodies as we age. Certainly genetic errors build up over time and are left uncorrected. But this is just one of many things that go wrong. The reason our bodies are allowed to degrade in the first place is because we have usually already survived well into our reproductive age. The evolutionary theories of aging actually provide a pretty solid explanatio…

Would it not make more evolutionary sense to remain reproductively capable for hundreds or thousands of years? The motive for genes to reproduce does not end after a single set of offspring. In fact, I don't think the motivation is even reduced.

If the Red Queen hypothesis (http://en.wikipedia.org/wiki/Red_Queen_hypothesis) is correct, failing to mutate (e.g. via long lifespans and continued reproduction) would be an evolutionary disadvantage. I don't know enough on the topic to have an opinion about the accuracy of the hypothesis, but it's something to think about when you think about this topic.

Re: Ageing: The girls who never grow older

#30

Post by ars » Wed, May 21, 2014, 6:39 AM UTC

jostmey wrote: post #28

ars wrote: post #27

Earlier quoted context omitted.

> No, I am not. I assumed that the offspring will die of old age too. How does that change the conclusion? 3 children vs 2 is still immensely more children, not just a marginal amount as you thought.

When that third child is being born the second child is already beginning to reproduce (if you reproduce like Yeast). Clearly, that second child is more important because it has already given you a grandchild when your third child is still in the process of being born. That second child has already resulted into two offspring, and counts for twice as much.

That only matters at a specific moment in time, but if you take a slightly longer view that 3rd child had an enormous impact.

> That second child has already resulted into two offspring, and counts for twice as much.

Only for one generation, but we care about many many generations. 10 generation down the line the slight difference in timing makes no difference.

But the increase in number made an enormous difference.

You really need to sit and run some numbers and you'll see you are mistaken.

Maybe your intuition will help you if think of it as a steady state - babies in (born), babies out (die), rather than thinking about one moment in time. In a steady state the timing make no difference (because you've already waited out the time) - only the number matters.