I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
MY understanding is that the elderly act as grandparents to the younger generation because they can't have more children. By having this second set of care/parenting it positively reinforces its standing stays in the gene pool. This helps generations live by having both sets of parents. It can work both ways if they are a negative influence on the children or whatnot, then the group will weed out the oldies.
hopefully I read your question right im really tired right now
The best point of evidence for (2) is Huntington's disease. Almost 100% lethal, autosomal dominant, generally begins to present post-reproduction. The only way it would be "filtered out" is if began avoided reproducing with those with parents positive for the condition (which is indeed the case). It will almost never filter out naturally in a non-sentient population.
The other point of view is that genetic mutations rarely exist in a vacuum. Some, like Huntington's, are purely a death sentence. Others, like sickle cell anemia, actually present mortality benefits in some areas (like malarial infection). Many mutations that are "benefiting diseases" may actually be helping individuals pass their genes on in an earlier stage of life.
From the genetic standpoint, #2 is generally correct. Once you have reproduced a few times, everything in your genes that could kill you after that point is not affected by the evolutionary pressure, since even if you end up dying from it, your offspring will already be born with the same gene.
Of course there are some advantadges in not dying immediately after your first son is born (or even concieved, a la praying mantis); you still need to provide him a shelter for his first couple of years in order to guarantee your genetic lineage going on, and you can have more progeny the longer you are alive while able to reproduce. However, after the reproductory capabilities are lost, there is no evolutionary pressure in place anymore, and that is probably the main reason why elderly people tend to get sick, their organs tend to stop functioning properly, and ultimately end up dying: the genetic pool does not need them anymore.
I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
Cheers guys!
Elderly people are useless? Whether its for humans or other animals, these are the ones who hold most if not all knowledge (for example, to lead them to water in times of drought). Gay gene?
But ok.
Name me one disease that only affects elderly people and can't occur for younger people in a similar physical condition?
You shouldn't forget about the knowledge that older people/animals accumulate and potentiall pass on to their younger ones. Especially knowledge about relatively rare phenomena, say like an extremly dry year is important here. The oldest ones in a herd might have experienced such a situation before and have learnt (when they still were young) where to still find water. If no such knowledge is present, the whole herd might die.
You ask a difficult question which has no two-line answer - at present, I doubt it has any of satisfactory answer whatsoever. I will try to provide a very not short and probably not directly answering reply.
Your main idea, that dying before reproductive age is much more heavily selected against and will be filtered out more quickly than post-menopausal conditions, is pretty much correct.
Your subsequent claim, that dying in late puberty rather than infancy is more detrimental, requires more argument. Thinking in terms of group selection is generally not a good idea. It gives completely different answers, depending on what level of groups you are looking at - husband-and-wife, family, tribe, species, ecosystem - and there are no good arguments for which level is the right one. Good thinking requires you to look at the level of genes.
If the late-puberty-death should be selected against more heavily than early-infancy-death, you would have to show that it affects the fitness of other carriers of the gene negatively, and overall more negatively than it affects non carriers.
Your overall conclusion is most likely sort of right though - particularly the mother invests a lot of resources in a child between infancy and puberty, which would otherwise likely have contributed to other, healthier children, which would have reproduced. For instance, women tend not to get pregnant while breastfeeding. Furthermore, the mother will probably have to be a carrier of a recessive gene for this condition.
This might seem pedantic, but careless group-selection arguments can easily lead you to false conclusions, for instance when it comes to aggressive behavior.
So, closing in on your actual question - how do post-menopausal genetic diseases get filtered out? The short answer is - they don't. For instance, the link below claims that only three species tend to live past menopause, and for humans, this is at least partially because of modern living conditions and medicine: http://www.livescience.com/22574-animals-menopause.html
If you study in some detail what happens to people in old age, there tend to be a lot of different things racing to kill them off - various cancers, heart attacks, organ failures, Alzheimer's - and all this is happening while the body as a whole is deteriorating - loss of vision, muscle mass, weakened immune system. Having a better genetic basis for surviving one of these cancers and whatnot will still only marginally lengthen your life span, which will at best have a tiny, positive effect on your fitness. There seems to be sort of an expiry date on a human body which is pretty much planned for all along.
Even so, you have hypotheses that there aren't individual genes for getting cancer at an old age, but that they really tend to have a sort of lifetime investment profile, with the same gene contributing positively in adolescence and negatively later on. As a crude example, there is generally a trade-off between rapid growth and longevity.
In my opinion, there is a much better question than why do old people die?, and that is, why do people lose their ability to reproduce a good while before they die?. On the surface of things, you would expect the reproductive function to be the one that the body stubbornly holds on to while everything else is shutting down. And as you saw in the link above, menopause is not at all a common phenomenon in nature. The link names the grandmother hypothesis, which is sort of one thing you suggested, which is just a name for having old people help their own genes along by working for their close family, who tend to share their own genes. Note that a woman is, on average, as closely related to her her sister as she is to own children, and that providing any sort of support to her own grandchildren is not all that much worse having her own children. http://www.livescience.com/9024-women-whales-share-rich-post-breeding-life.html
You might also want to have a look at this graph, which shows that the incidence of Down's syndrome - which tends to lead to infertility in addition to everything else - increases exponentially with the maternal age: http://www.aafp.org/afp/2000/0815/afp20000815p825-f1.gif
Now, you can point the arrow of causality in either direction - since the risk of mothering unhealthy children is growing so quickly, reproduction should shut down around the age of forty, or - since reproduction is about to shut down around this age, the pressure to maintain reproductive integrity is dwindling.
My main intention with all this rambling is to show that pretty much nothing is obvious. There are lots of trade offs in nature, and common sense explanations are not always good enough. To really set things straight, you need to get down with the details and do complicated mathematical modelling to understand which mechanisms which do sort of make sense but make no real contribution and how stuff really works. For instance, group selection is pretty much disfavored by most current scientists, mostly replaced by kin selection and reciprocity.
And, well, unfortunately, we really do not have the final answers to the questions you ask. It is obvious that, an aging body which cannot reproduce would be put to better use by helping out its close family than simply wandering off and dying, but it is not at all obvious why reproduction should eventually be completely shut down in women and gradually sort of fade out in men - a pregnancy might be too much to handle in old age, but producing a few healthy sperm?
Why some people turn out gay, which seems to be a fairly simple question, turns out to be more than we can answer today.
Finally, overdoing the teleological explanations, and assuming that sort of everything which happens in nature has to have some sort of clever purpose, might itself be mistake. Perhaps the prevalence of homosexuality is mostly an incidental result of the two sexes being fairly similar. Once you are done doing kin selection arguments for homosexuality, you need to explain why some people have the weirdest of obscure fetishes.
If you are interested in reading a good explanation of natural selection at the level of genes rather than individual organisms, I would heartily recommend Richard Dawkins - The Selfish Gene.
Other posters have chimed in on the value that older people provide to a group with experience and extra hands to help out, so groups that have older people around to help out can do better than those without. Of course, there also comes a point where those people become a hindrance since their burden becomes larger than the benefit.
But from my understanding, a lot of genes are double-edged swords that are very useful for reproduction but cause problems later in life. Testosterone obviously has a huge positive effect on humans, but it also weakens our immune system to the extent the eunuchs live 13.5 years longer on average than normal man.
I think your initial assumption that they are filtered out is wrong, and they are only somewhat filtered out in groups where non-reproducing members can be still be a benefit.
I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
Cheers guys!
Elderly people are useless? Whether its for humans or other animals, these are the ones who hold most if not all knowledge (for example, to lead them to water in times of drought). Gay gene?
But ok.
Name me one disease that only affects elderly people and can't occur for younger people in a similar physical condition?
I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
Cheers guys!
Elderly people are useless? Whether its for humans or other animals, these are the ones who hold most if not all knowledge (for example, to lead them to water in times of drought). Gay gene?
But ok.
Name me one disease that only affects elderly people and can't occur for younger people in a similar physical condition?
Alzheimer's?
I was going to say the same, but apparently, there is this thing called early onset Alzheimer's. The question is incredibly unfair though - there are a lot of diseases which are vastly more prevalent among the elderly.
I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
Cheers guys!
Elderly people are useless? Whether its for humans or other animals, these are the ones who hold most if not all knowledge (for example, to lead them to water in times of drought). Gay gene?
But ok.
Name me one disease that only affects elderly people and can't occur for younger people in a similar physical condition?
Alzheimer's?
I was going to say the same, but apparently, there is this thing called early onset Alzheimer's. The question is incredibly unfair though - there are a lot of diseases which are vastly more prevalent among the elderly.
Obviously, because we get weaker. But that's my entire point. These diseases and whatever impact our genetics have on them, and they on our genetics, aren't exclusive to elderly people...
I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
Cheers guys!
Elderly people are useless? Whether its for humans or other animals, these are the ones who hold most if not all knowledge (for example, to lead them to water in times of drought). Gay gene?
But ok.
Name me one disease that only affects elderly people and can't occur for younger people in a similar physical condition?
Alzheimer's?
I was going to say the same, but apparently, there is this thing called early onset Alzheimer's. The question is incredibly unfair though - there are a lot of diseases which are vastly more prevalent among the elderly.
Obviously, because we get weaker. But that's my entire point. These diseases and whatever impact our genetics have on them, and they on our genetics, aren't exclusive to elderly people...
I get your point, but I still think it's a rather poor one. You are technically right as long as we talk in the absolutes of never, can't and exclusive, but there are most definitely diseases which for most practical purposes can be considered to only affect the elderly - such as, for the purpose of contributing meaningfully to natural selection, which is the discussion at hand.
I'm not sure what the best examples are, but Alzheimer's, prostate cancer and Huntington's are all candidates.
I think it's a valid point that these diseases could happen at anytime, but there is some genetic mechanism to keep them in check until after reproduction, or in the case of Alzheimer's, well after reproduction has stopped and when group selective pressure might actually push them to die since they're becoming a burden.
There's no right or wrong answer to selection theories based on evolution. If it makes sense, then maybe it is so, but it's often surprisingly easy to argue for diametrically opposed views of how evolution has come to benefit a trait.
Overall I'm thinking that throughout human evolution, people never really got old enough to no be able to reproduce, so it's never really been an issue. Maybe a few of the high-status individuals were able to do so, but just a few hundred years ago people simply died young.
On June 14 2013 00:46 Sablar wrote: There's no right or wrong answer to selection theories based on evolution. If it makes sense, then maybe it is so, but it's often surprisingly easy to argue for diametrically opposed views of how evolution has come to benefit a trait.
Overall I'm thinking that throughout human evolution, people never really got old enough to no be able to reproduce, so it's never really been an issue. Maybe a few of the high-status individuals were able to do so, but just a few hundred years ago people simply died young.
People didn't all die at the age of thirty in the past. The low life expectancy in poorer societies is primarily a result of high mortality among infants and children.
Upper Paleolithic, 33, Based on data from recent hunter-gatherer populations, it is estimated that at age 15, life expectancy was an additional 39 years (total age 54).
Classical Rome[14], 28, At age 15, life expectancy an additional 37 years (total age 52).
Medieval Britain[17][18], 30, At age 21, life expectancy an additional 43 years (total age 64).[19]
Menopause occurs around the age of fifty, and women generally live longer than men.
On June 13 2013 22:34 TheTenthDoc wrote: The other point of view is that genetic mutations rarely exist in a vacuum. Some, like Huntington's, are purely a death sentence. Others, like sickle cell anemia, actually present mortality benefits in some areas (like malarial infection). Many mutations that are "benefiting diseases" may actually be helping individuals pass their genes on in an earlier stage of life.
I'm really glad I asked this question here.
This point seems really obvious when reading it now, but it didn't cross my mind once when pondering the issue and it's also a very important thing to consider. Thanks a lot!
On June 13 2013 23:51 Darkwhite wrote: PLADR (Pretty long absolutely did read)
Thanks so much for the detailed answer and the time you took to answer my post.
This pretty much cements my decision to study biology next semester, what a fascinatingly complex field.
Btw, I'm a third of the way through 'The Selfish Gene', which is why the question came up in the first place.
I'm just reading up a little on how evolution works and I have a quick and simple question. My grasp on the subject is very limited, so you might have to be a little patient. Please point out obvious fallacies.
How are genetic mutations that benefit post-menopausal (as in: after an organism loses the ability to procreate) diseases "filtered out"?
Let's assume there's a genetic mutation that benefits cancer in infants. As this mutation prevents them from procreating, it will be "filtered out" rather quickly.
A mutation that has the same effect but occurs a little later in life, right before sexual maturity will be filtered out even more quickly, as - thinking in terms of group selection - a dead "almost-adult" is a bigger detriment to the group, having taken more nurturing from the group without providing an evolutionary benefit.
It's thus obvious that evolution filters out genetic constellations that benefit deadly diseases before the procreation-period is over.
Which brings me to my point:
How are genetic mutations that benefit diseases that occur in old organisms, such as elderly people, filtered out?
There's two solutions I could come up with that make some sense sense to me, but both aren't really satisfying:
1. I feel like the answer lies in group selection, as there might be a benefit to have elderly people or animals in your pack / peck / herd / group / village etc., but I fail to see what that benefit is. Then again, gayness doesn't seem to have an obvious benefit to group selection and the "gay gene" (lol) must have been around for millennia.
2. Maybe my initial assumption that they are indeed filtered out is simply wrong and that's why there's a million diseases that only affect old people and the only reason you see them around is how advanced medicine has become.
Cheers guys!
Elderly people are useless? Whether its for humans or other animals, these are the ones who hold most if not all knowledge (for example, to lead them to water in times of drought). Gay gene?
But ok.
Name me one disease that only affects elderly people and can't occur for younger people in a similar physical condition?
No need to be so aggressive, as has been pointed out, "the elderly" i. e. post-"menopausal" specimen of a species are almost exclusive to humans.
The "gay gene", which I deliberately put into inverted commas, is discussed here:
You should see evolution as an observation, not as a mechanism or a goal.
You mention that evolution does this or that, but that's thinking the wrong way around.
Procreation with any deviation is the basic mechanism that gives rise to evolution. People in this thread are describing more abstract mechanisms. But I think in modern times due to healthcare and medicine, all bets are off with regards to evolution. Personally I believe there will be a big regression in terms of susceptibility to disease as they matter less for survival and procreation but perhaps the more intercultural less-local mating gives many benefits to compensate. I'm waiting for a relaxation of ethical objections against laboratory genetic manipulation of human genes.
Also, I'd like to inform you that the possible fleas jumping on your skull are as evolved as you, as are all currently living things that have a potential for, or already have offspring. The existence of a living organism is testament to its predecessors' success. (And we humans are as dependent on our gut bacteria as (human compatible) fleas are to us, for example.)
If anything, diseases which kill off the elderly are selected for, as they reduce the strain put on the younger, more able bodies population. I remember reading an article on this relating cancer to it a long time ago.
EPT
