Natural selection, evolution "why are we still sick"

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Now first of all biology is not my strong subject but I am interested in it nevertheless,
if my questions come off as arrogant or ignorant then pardon and please explain as I am curious.


Last night before going to sleep I suddenly stumbled upon a question, the question goes somewhat like this, "If evolution works the way we think then why the percentage of people having birth defects and other deficiencies like cancer in almost every generation, haven't decreased?"

I mean natural selection is basically like a engineering feedback loop and as the saying goes "survival of the fittest" we know that organisms that have a tendency to develop severe drawbacks like cancer etc are less likely to reproduce or survive , in fact this saying can be attributed to great many things and it still sounds valid.
Yet somehow when we look at the human history we can see that throughout the ages birth defects haven't decreased, and my thinking goes something like this, we have good healthcare only for the last 100 years and even then not in all parts of the world, so we could safely assume that for most of the known human history surviving was a tough game and so the ones that were less likely to survive most likely died either as infants or very young, I wonder why hasn't this "cleaned" the human population's genetic heritage throughout the ages so that by today there would be mostly healthy people and very few genetically defective cases?

Cancer is a good example to my mind, I wonder what makes it so resistant to thousands of years or natural selection?




Also a little offtopic hypothesis, would it be safe to assume that thanks to modern medicine and technology much more sick and severely ill people can survive and even reproduce that this is working against natural selection and increasing the percentage of less robust people and given enough time and more technological advancement the whole civilization could become much more prone to new viruses and outside obstacles which would increase the medical bills and infrastructure spending and so collapse a society or a civilization
 

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  • #2
Drakkith
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I mean natural selection is basically like a engineering feedback loop and as the saying goes "survival of the fittest" we know that organisms that have a tendency to develop severe drawbacks like cancer etc are less likely to reproduce or survive , in fact this saying can be attributed to great many things and it still sounds valid.
"Survival of the fittest" is better understood as "survival to reproduce". By that I mean that natural selection only cares about keeping organisms alive long enough to maximize their reproduction in the best way as to pass on their genes. You might think that an organism that lives almost forever and constantly reproduces would be selected for, but this ignores all the stuff happening to their offspring. Let's say that such an organism exists and has just reached sexual maturity and found a mate. Let's also say that their first offspring has a mutation in their DNA that inhibits that offspring's DNA repair mechanism, greatly increasing the chance of accumulating the genetic errors that eventually lead to cancer.

Now, this offspring doesn't develop cancer immediately, as it takes time for these genetic errors to accumulate in their DNA. So this offspring survives long enough to have several offspring and ends up passing the mutated genes for the "damaged" DNA repair mechanism along to their offspring. Since the detrimental effect of this mutation isn't felt until these organisms have already had multiple offspring, natural selection cannot effectively select against it. Over time this particular gene would potentially spread throughout the population.

Note that if this mutation was in a critical gene, such as one of the genes that builds proteins for ATP synthesis (the series of chemical reactions that creates fuel for every cell), then this mutation would be so detrimental that the organism probably wouldn't survive to sexual maturity and the mutation would be heavily selected against.

Yet somehow when we look at the human history we can see that throughout the ages birth defects haven't decreased, and my thinking goes something like this, we have good healthcare only for the last 100 years and even then not in all parts of the world, so we could safely assume that for most of the known human history surviving was a tough game and so the ones that were less likely to survive most likely died either as infants or very young, I wonder why hasn't this "cleaned" the human population's genetic heritage throughout the ages so that by today there would be mostly healthy people and very few genetically defective cases?
Evolution doesn't generate "perfect" organisms. It generates "good enough" organisms. We're good enough to survive to pass on our genes effectively, despite the occasional severe defect. Also, keep in mind that the entire process of building, maintaining, and copying DNA is an exceedingly complex task. The mechanisms we have in-place work wonderfully well, but they aren't perfect and they can't be perfect. Even the organisms with the best DNA repair mechanisms, with multiple copies of their DNA for redundancy, cannot avoid mutations creeping in over time.
 
  • #3
Laroxe
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Only a minority of conditions are exclusively cause by genes, there are always issues like nutrition and environmental toxins which may cause genetic changes during a lifetime, a lot of these will also be cumulative over time. Because we are beginning to understand this some problems actually are becoming less common, e.g. neural tube defects. Some single gene defects are now screened for and parents given genetic counseling which should also effect the incidence.
A few ideas to consider; cancer is overwhelmingly a disease of old age so has very little impact on fitness. Only conditions which effect reproduction will effect selection. It could be argued that natural selection makes sure that people die when they can no longer reproduce, after our reproductive peak the probability of dying doubles every 8 years, we don't just wear out, we accelerate towards our death. (It always cheers me up that one.:))
The role of viruses in causing genetic changes is only just starting to be understood and is of increasing interest in cancers effecting the young.
In every cell division there is the possibility of mistakes in the copying of the DNA, most are detected and the cell destroyed but minor damage can accumulate over time with each division.
In some conditions the pattern of inheritance means the genes that cause a problem can be present in people unaffected and who continue to reproduce.
Some genes that may predispose people to a particular problem may have an important alternative function, it is the adaptive function which has the bigger effect on selection, the gene that causes sickle cell anemia also increases resistance to malaria.
 
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thanks both of you for the answers, not to sound arrogant but much of that I already knew,
you know while we are on the subject, I wonder there are many families around the world both famous and not so and also many of whom I know personally that have this so called "cancer gene" as in almost every generation atleast one or sometimes more people wihin the same blood relative group get cancer, usually those are men and around 40/50 sometimes 60+ but recently in their family a younger woman got cancer she is about 25 I believe. She underwent therapy and atleast for now the cancer is gone but still this makes me wonder, it almost feels like natural selection curses certain people...

I guess what I am wondering about is why would such a recipe for a defective outcome survive so many generations without being checked and diagnosed by the body's own internal safety systems.


P.S. What I read about your answers regarding the reproductive age and how natural selection only cares about that we make until we reproduce it sort of reminds me of a modern car dealership which only cares until your warranty ends and then you can go and die...:D
 
  • #5
Laroxe
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While all cancers involve genes, really there is no such thing as a cancer gene, for cells to become a cancer usually requires a number of mutations. They need to be able to ignore the usual controls over cell division, they have to be able to ignore the controls that keep it in its place within the body , they need to develop ways of avoiding being destroyed by the immune system etc.. There are various ways that cells can do this, some more effective than others and lots of other mutations can be present. There are also differences in the way different tissues use the different mechanisms and most cancers when they develop undergo further mutations at an increasing rate.
Most cancers occur because of mutations that occur during a persons life, generally genetic mutations that are inherited tend to effect one of these areas basically reducing the number of mutations needed and so increasing risk. Some examples would be the BRCA1 and BACA 2 genes which are part of the control system in cell division and are referred to as tumour suppressor genes. Abnormalities in these greatly increase the risk of breast cancer, increase the risk of ovarian cancer and the BACA 2 increases the risk of prostate cancer. However there are lots of genes that can have a variable effect on the risk of specific cancers, none of these genes has the job of causing cancer, they all have other functions so usually cancers reflect a failure of the gene to do its job. Abnormalities that are inherited are often present in a large number of cells which again effects risk.
People often like to think of nature as having motives, they talk about mother nature, the natural balance and the idea that natural =good, the fact is that there is nothing particularly nice or benign about the natural world. Life competes for its place in the world and natural selection is like an ongoing experiment with no ethics committee. Mutations are built into the system, it can increase diversity but usually it doesn't, most mutations are harmful. Even the ones that are not harmful still need a great deal of luck, they need to reach reproductive age, successfully reproduce, their children need to survive and so on. Nature doesn't care because it can't care, life is, as Dawkins said, “Amoral and persistent”. Why do you think its defective? despite the fact that 99% of all species that have ever lived are now extinct, there are more species now than there have ever been, death makes space for the new.
 
  • #6
Drakkith
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I guess what I am wondering about is why would such a recipe for a defective outcome survive so many generations without being checked and diagnosed by the body's own internal safety systems.
Generally, a cell cannot check to see if a particular gene is defective or not. DNA damage can be found, but a mutation leading to a defective gene is not damage (though it may be caused by damage). The DNA strand is perfectly functional and intact. That particular portion is just coding for the wrong thing. This is especially true for genes that were inherited as-is. The cell just has no way of knowing what genes are "supposed to do". And in reality, genes can't be said to have some set purpose. If a mutation in a gene creates white spots on an animal instead of a brown coat, we can't say that the spotted-fur gene is "supposed to make brown fur". It's not supposed to do anything other than what it actually does.

So when a cell's DNA reading machinery chugs along the strand and comes across a gene that no longer codes for a cancer preventative compound due to a mutation, the machinery has no idea what that gene is supposed to do. It just chugs right along, transcribing away, oblivious to anything other than the DNA it's immediately working with.
 
  • #7
BillTre
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There cases where an adult animal past its reproductive prime can still be of adaptive value and therefore selected for.
It has been hypothesized that in some species old adults are reservoirs of knowledge about their environment, such as where are the water holes in the desert or what is the best migration path in certain situations.
 
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russ_watters
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"If evolution works the way we think then why the percentage of people having birth defects and other deficiencies like cancer in almost every generation, haven't decreased?"
Cancer and birth defects are the result of genetic errors/defects; some of the same type of errors that feed evolution. With genetic errors, sometimes you get an advantage and sometimes you get something fatal.
Also a little offtopic hypothesis, would it be safe to assume that thanks to modern medicine and technology much more sick and severely ill people can survive and even reproduce that this is working against natural selection and increasing the percentage of less robust people and given enough time and more technological advancement the whole civilization could become much more prone to new viruses and outside obstacles which would increase the medical bills and infrastructure spending and so collapse a society or a civilization
I don't know about working against evolution(evolution doesn't have a goal to work "against"), but definitely impacting its path.
 
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Laroxe
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There cases where an adult animal past its reproductive prime can still be of adaptive value and therefore selected for.
It has been hypothesized that in some species old adults are reservoirs of knowledge about their environment, such as where are the water holes in the desert or what is the best migration path in certain situations.
Your right, there are some good reasons to assume that human longevity can improve the fitness of their children, but because its outside of their own reproductive period it can't have any impact on their own fitness. Remember fitness is a measure of reproductive success and as longevity occurs outside of the reproductive period, it can't be selected, though things like immunity which would help, could be. Unfortunately it isn't just humans that evolve, so does everything else and that includes our pathogens, all of life is in competition for resources and to improve its own fitness.
 
  • #10
Drakkith
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Remember fitness is a measure of reproductive success and as longevity occurs outside of the reproductive period, it can't be selected, though things like immunity which would help, could be.
Sure it can. If the genes responsible for increased longevity increase the chance of an organisms' children or grandchildren (who are also very likely to have these same genes) surviving to reproductive age, perhaps because the longer lived organism can take help take care of them, then natural selection can act on the genes. For example, if an organism without these genes died and, because of their absence, their grandchildren died, then their genes would not be passed on. Over time the genes promoting longevity would spread as a natural result.
 
  • #11
Laroxe
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Sure it can. If the genes responsible for increased longevity increase the chance of an organisms' children or grandchildren (who are also very likely to have these same genes) surviving to reproductive age, perhaps because the longer lived organism can take help take care of them, then natural selection can act on the genes. For example, if an organism without these genes died and, because of their absence, their grandchildren died, then their genes would not be passed on. Over time the genes promoting longevity would spread as a natural result.
There are lots of things that could potentially impact on the survival of grandchildren and indeed of grandparents a number of these will be part of the evolutionary arms race and so unlikely to have a consistent effect. The next issue would be in how much advantage would be conferred, I imagine this would be in the first few years of the grandchilds life, when the grandparents would still be relatively young. There does come a point at which the grandparents might in fact become a burden to the young, I'm just not sure that natural selection could or would be that selective. As longevity increases this is now a political issue and is seen as a threat at the level of society, to the resources available to the young.
I do take your point but I think there are far to many variables involved, I suspect a mathematician could work it out, but I couldn't find any that have.
 
  • #12
Drakkith
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I do take your point but I think there are far to many variables involved, I suspect a mathematician could work it out, but I couldn't find any that have.
I'm not presenting a novel idea here. Darwin himself proposed a similar idea to explain the sterility of honeybee workers in his book The Origin of Species. The mechanism is known in modern times as kin selection: https://en.wikipedia.org/wiki/Kin_selection

There are lots of things that could potentially impact on the survival of grandchildren and indeed of grandparents a number of these will be part of the evolutionary arms race and so unlikely to have a consistent effect.
From an article on the evolution of grandparents by scientific american:

We do not know exactly what those Upper Paleolithic Europeans started doing culturally that allowed so many more of them to live to older age. But there can be no doubt that this increased adult survivorship itself had far-reaching effects. As Kristen Hawkes of the University of Utah, Hillard Kaplan of the University of New Mexico and others have shown in their studies of several modern-day hunter-gatherer groups, grandparents routinely contribute economic and social resources to their descendants, increasing both the number of offspring their children can have and the survivorship of their grandchildren. Grandparents also reinforce complex social connections—like my grandmother did in telling stories of ancestors that linked me to other relatives in my generation.

Elders transmit other kinds of cultural knowledge, too—from environmental (what kinds of plants are poisonous or where to find water during a drought, for example) to technological (how to weave a basket or knap a stone knife, perhaps). Multigenerational families have more members to hammer home important lessons. Thus, longevity presumably fostered the intergenerational accumulation and transfer of information that encouraged the formation of intricate kinship systems and other social networks.
It goes on to explain that the evolution of grandparents increases the population size, accelerating evolution by increasing the number of mutations and opportunities for positive mutations to spread throughout populations as their members reproduce. It seems plausible to me that this combination of increased number of offspring from their children, increased survival rate of these offspring, and larger population size could have led to strong selection pressure.

Below are a two more references from the many that I found.

Postmenopausal longevity may have evolved in our lineage when ancestral grandmothers subsidized their daughters' fertility by provisioning grandchildren, but the verbal hypothesis has lacked mathematical support until now. Here, we present a formal simulation in which life spans similar to those of modern chimpanzees lengthen into the modern human range as a consequence of grandmother effects. Greater longevity raises the chance of living through the fertile years but is opposed by costs that differ for the sexes. Our grandmother assumptions are restrictive. Only females who are no longer fertile themselves are eligible, and female fertility extends to age 45 years. Initially, there are very few eligible grandmothers and effects are small. Grandmothers can support only one dependent at a time and do not care selectively for their daughters' offspring. They must take the oldest juveniles still relying on mothers; and infants under the age of 2 years are never eligible for subsidy. Our model includes no assumptions about brains, learning or pair bonds. Grandmother effects alone are sufficient to propel the doubling of life spans in less than sixty thousand years.
Ref: http://rspb.royalsocietypublishing.org/content/279/1749/4880

Two striking differences between humans and our closest living relatives, chimpanzees and gorillas, are the size of our brains (larger by a factor of three or four) and our life span (longer by a factor of about two). Our thesis is that these two distinctive features of humans are products of coevolutionary selection. The large human brain is an investment with initial costs and later rewards, which coevolved with increased energy allocations to survival. Not only does this theory help explain life history variation among primates and its extreme evolution in humans; it also provides new insight into the evolution of longevity in other biological systems. We introduce and apply a general formal demographic model for constrained growth and evolutionary tradeoffs in the presence of life-cycle transfers between age groups in a population.

We present a theory of life history evolution, which integrates biological theory and the economic theory of capital. We first review the evidence on the evolution of brain size and longevity and present our theory informally. The formal model is outlined next, including its key implication that a more challenging environment, one in which learning by doing plays a larger role, selects for both a larger brain and lower mortality. Three lines of relevant empirical evidence are then considered, and the paper concludes with a brief discussion of the implications of our theory.
Ref: http://www.pnas.org/content/99/15/10221?ijkey=9d5d05b7d56a5981cf59c4fdffb2e4ca493149c2&keytype2=tf_ipsecsha
 
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jim mcnamara
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  • #15
Laroxe
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I'm not presenting a novel idea here. Darwin himself proposed a similar idea to explain the sterility of honeybee workers in his book The Origin of Species. The mechanism is known in modern times as kin selection: https://en.wikipedia.org/wiki/Kin_selection



From an article on the evolution of grandparents by scientific american:



It goes on to explain that the evolution of grandparents increases the population size, accelerating evolution by increasing the number of mutations and opportunities for positive mutations to spread throughout populations as their members reproduce. It seems plausible to me that this combination of increased number of offspring from their children, increased survival rate of these offspring, and larger population size could have led to strong selection pressure.

Below are a two more references from the many that I found.



Ref: http://rspb.royalsocietypublishing.org/content/279/1749/4880



Ref: http://www.pnas.org/content/99/15/10221?ijkey=9d5d05b7d56a5981cf59c4fdffb2e4ca493149c2&keytype2=tf_ipsecsha
Thanks for the extensive reply, I am aware of the ideas around kin selection and generally think they are pretty sound, it provides a framework for making sense out of a lot of human behaviours, but like a lot of such frameworks its easy to over extend. A common criticism in evolutionary psychology is that there is a tendency to develop an idea and build a story around it, I think the grand mothering hypothesis ( Its not grand parenting!) is an example of this.
The first and perhaps most damning problem is that natural selection works at the level of the individual, it involves heritable traits that improves that individuals reproductive success, there is no mechanism for predicting that a grandparent might be useful. Even if there were it can still only select traits that are already present, so we still have no explanation of how longevity evolved only a claim that it is useful. In fact the idea of an animal sacrificing their own fitness to benefit another is very unusual in nature, social insects are clones they are protecting their own genes and in the example of chimps longevity it states “Greater longevity raises the chance of living through the fertile years.” this is not the same thing at all.

Its noticeable that the theory totally ignores the grand father though notes that generally women have a longer lifespan, this is only a matter of a few years, its not a good enough reason to ignore the issue. It does however seem almost axiomatic that having a grand mother help with the child rearing of blood relatives would be of benefit and help more of the children survive. Of course this does mean we have to ignore the fact that throughout history in societies where the population of the elderly increases, the number of children actually fall. It is also problematic that in many tribal groups where the elderly have a clear role in childcare, this usually involves shared childcare for the whole group. For many in evolutionary psychology any invocation of group selection, however vague, is heresy.

This is one little test of the idea but actual evidence supporting the claims is thin on the ground, I simply don't think it makes much sense as the product of natural selection, its not really the way it works.

https://www.ncbi.nlm.nih.gov/pubmed/18322917
 
  • #16
Drakkith
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The first and perhaps most damning problem is that natural selection works at the level of the individual, it involves heritable traits that improves that individuals reproductive success, there is no mechanism for predicting that a grandparent might be useful.
The papers I just linked, and others like them, are strong refutations of this.

Even if there were it can still only select traits that are already present, so we still have no explanation of how longevity evolved only a claim that it is useful.
Obviously natural selection acts only on traits that are present, since traits that aren't present can't be acted upon. However the traits themselves arise from mutations in the DNA. Once a trait arises, it can spread throughout a population through genetic drift until further mutations increase its effect to a degree large enough for natural selection to take over, or, if the effect is large enough, natural selection can immediately begin acting on it.

In fact the idea of an animal sacrificing their own fitness to benefit another is very unusual in nature
Can you support this claim with a valid reference?

social insects are clones they are protecting their own genes
I can't say much in a general sense, but in the case of the honey bee, this is not correct. First, each egg laid by the queen contains only half of her genes and any two offspring are extremely unlikely to have an identical set of genes from their mother. Second, queens mate with multiple drones and use their sperm to increase the genetic diversity of the colony. This further decreases the likelihood that and two offspring are genetically identical.
Ref: http://www.glenn-apiaries.com/principles.html

and in the example of chimps longevity it states “Greater longevity raises the chance of living through the fertile years.” this is not the same thing at all.
After reading more on this, I agree it's not quite the same thing.

Its noticeable that the theory totally ignores the grand father though notes that generally women have a longer lifespan, this is only a matter of a few years, its not a good enough reason to ignore the issue.
I'm willing to bet that it was ignored in order to simplify the model. Note that the paper is about a particular model, not about the theory as a whole.

It does however seem almost axiomatic that having a grand mother help with the child rearing of blood relatives would be of benefit and help more of the children survive. Of course this does mean we have to ignore the fact that throughout history in societies where the population of the elderly increases, the number of children actually fall.
The ratio of elderly to young adults has changed in modern times because adults in well developed nations tend to have fewer children than they did in the past, coupled with an increase in the average lifespan of the elderly by upwards of one to two decades. This is caused by the extreme change in our society from an agrarian culture without modern medical care to an industrialized culture with highly effective health care, and with all of the social changes that such a transition brings.

This is one little test of the idea but actual evidence supporting the claims is thin on the ground, I simply don't think it makes much sense as the product of natural selection, its not really the way it works.

https://www.ncbi.nlm.nih.gov/pubmed/18322917
From the article:
In this article, we test the mother and the grandmother hypotheses with a historical data set from which we bootstrapped random samples of women from different families who lived from the 1500s to the 1900s in the central valley of Costa Rica.

So to test the evolution of longevity they decided to use data from a near-modern society, from a species who, as a whole, had already evolved longevity? I know I'm not qualified to really judge this paper, but it seems questionable to me.
 
  • #17
Laroxe
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As I said, I think its easy to get carried along with a good theory and inclusive fitness fits the bill for a good theory. I just think its important to try to examine ideas based on their own individual merits, the history of an idea is not evidence, but it can be seductive. While longevity can be explained by inclusive fitness, I don't think that excuses it from the very basic idea that natural selection is driven by the enhanced fitness of an individuals genes. A child does not pass on its genes to their parents natural selection in a biological sense, can only work when we are fertile and capable of having children. One of the problems is in attempting to explain how natural selection influences the fitness of individuals who can no longer reproduce, it sort of implies that old “mother nature”, has not only avoided the menopause (an interesting thought experiment, the menopause as a cause of global extinction.) but is also psychic. I didn't include much ref. Material, I didn't have much time and prefer full text links, I've had a bit more time now.

I do agree that the theory is pretty convincing, but don't agree that the evidence is, what evidence there is might best be described as mixed, it doesn't discriminate in supporting this idea over others and some is contradictory.

This looks at population dynamics, while it supports the theory, the numbers are interesting. It doesn't really support the idea that this is a modern phenomenon or that medical advances play a significant part.
https://www.nature.com/articles/428128a

This paper as well as the research has a good review of alternative explanations for longevity and is one of the few that include explanations involving grandfathers. The grandfather hypothesis provides a very different explanation, but seems equally credible. One of the problems that need explaining is the menopause, which in itself degrades a woman's health and performance, why would evolution favor a helper, then cripple it.
http://www.demogr.mpg.de/papers/working/wp-2004-003.pdf

In fact one idea is that the menopause and longevity in females has nothing to do with the children but reflects the competition to increase fitness between males and females. Female longevity being an adaptation to the males continued fertility in old age.
http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1003092

In fact there is evidence that the involvement of maternal grandmothers does increase the survival of female grandchildren but may reduce survival in male grandchildren. In fact the effects on survival rates is quite variable and depends on the nature of the genetic relationship, the sex and a variety of other possible factors. This in fact would make sense in evolutionary terms in that it would advantage the grandmothers own genes at the expense of the grandfathers, so there would be a clear fitness effect.

Now, while I'm as credulous as the next person, I do think that the only drivers of selection that make sense are a result of human cultural change and the beneficiaries are not the children of their children, but the elderly themselves.
http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1005631

This brings us to the problem with bee's, I'm not sure what was running through my head when I talked about bee's, but it clearly wasn't genetics. My one excuse, and I feel its a good one, is that I am a product of my genes and therefore prone to random episodes of brain failure, I can therefore avoid any personal responsibility and blame my parents...... or grandparents......... In fact anyone. :)
 
  • #18
Drakkith
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As I said, I think its easy to get carried along with a good theory and inclusive fitness fits the bill for a good theory.
Certainly.

While longevity can be explained by inclusive fitness, I don't think that excuses it from the very basic idea that natural selection is driven by the enhanced fitness of an individuals genes. A child does not pass on its genes to their parents natural selection in a biological sense, can only work when we are fertile and capable of having children. One of the problems is in attempting to explain how natural selection influences the fitness of individuals who can no longer reproduce, it sort of implies that old “mother nature”, has not only avoided the menopause (an interesting thought experiment, the menopause as a cause of global extinction.) but is also psychic.
Hold on. What's this about natural selection influencing the fitness of individuals who can no longer reproduce? Natural selection does no such thing as far as I know.

This looks at population dynamics, while it supports the theory, the numbers are interesting. It doesn't really support the idea that this is a modern phenomenon or that medical advances play a significant part.
https://www.nature.com/articles/428128a
I think there's been a miscommunication here. I was talking about the fact that modern medicine has been one of the primary factors in the greatly increased average lifespan of people in modern, industrialized societies. That's not "longevity" in the sense that we're talking about here though. We as a species have already evolved longevity in the sense that we are capable of living for 70+ years unless disease or injury kills us early. Modern medicine and technology simply prevents/cures disease and injury.

This paper as well as the research has a good review of alternative explanations for longevity and is one of the few that include explanations involving grandfathers. The grandfather hypothesis provides a very different explanation, but seems equally credible. One of the problems that need explaining is the menopause, which in itself degrades a woman's health and performance, why would evolution favor a helper, then cripple it.
http://www.demogr.mpg.de/papers/working/wp-2004-003.pdf
It appears that this not a settled topic, as our various sources indicate. I was merely pointing out that as far as I knew, and according to plenty of sources that I found, natural selection could indeed act to spread a person's genes despite that person being beyond reproductive age. I will readily admit that I could be entirely wrong about the actual mechanism.

This brings us to the problem with bee's, I'm not sure what was running through my head when I talked about bee's, but it clearly wasn't genetics. My one excuse, and I feel its a good one, is that I am a product of my genes and therefore prone to random episodes of brain failure, I can therefore avoid any personal responsibility and blame my parents...... or grandparents......... In fact anyone. :)
No worries. I have several holes in my genes big enough to stick a hand through. But they're comfy, so I wear them around the house anyways. :biggrin:
 

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