Natural selection past the reproductive age

Discussion in 'Biology & Genetics' started by spuriousmonkey, May 17, 2004.

  1. spuriousmonkey Banned Banned

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    People assured other posters that it was possible that people past the reproductive age can have a possitive effect on the survival of 'their respective' groups.

    Is this true? and it is reverse also true.

    I posted the following in a different forum:

    I didn't get any satisfying answers there, but I am sure we can do better

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    So is it really possible to be under the influence of natural selection past your reproductive age?
     
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  3. ElectricFetus Sanity going, going, gone Valued Senior Member

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    The grandmother theory? The reason why we have grandparents is to help take care of the children, some sociologist claim that’s why grandmothers tend to live longer is that they help out more then grandfathers, I don’t agree with that.
     
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  5. paulsamuel Registered Senior Member

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    Yes:

    Inclusive Fitness

    (This is a response to the original post, not WCF)
     
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  7. spuriousmonkey Banned Banned

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    How does it work? I can't form a mental picture.
     
  8. ElectricFetus Sanity going, going, gone Valued Senior Member

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    aah old people help out, the children survive better, the genes propagate?
     
  9. spuriousmonkey Banned Banned

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    That is too easy. I can see that it would be beneficial for the whole group or species. But does it actually work.

    I used to think it was clear cut, but nowadays I am not so sure anymore because of what I said in the first post. The opposite must then also be possible.
     
  10. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Monkey: The theory is predicated on the idea that people can determine with some (any) degree of accuracy whether other people are related to them. If a grandparent tends to take care of their grandchildren better, then that "caring for your grandkids" trait will theoretically be selected for in the grandchildren.

    Now, some groups of primates seem to have relatively communal care for their children, and to a lesser extent for one another. If an entire breeding group is mutual in their care for one another, I'm not sure if inclusive fitness is still a factor.
     
  11. paulsamuel Registered Senior Member

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    sure it is. if the social groups are familial (which for primates, they are), then anyone you help in your group shares some proportion of your genes. you wouldn't even need a recognition factor. if an individual is in your group, then you share/help. that's all the recognition one needs.
     
  12. BigBlueHead Great Tealnoggin! Registered Senior Member

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    True, but in this case inclusive fitness has no gradient within the group, only between... on the other hand, I suppose we consider the species population as a whole when we're talking about natural selection, and so the degree of communal care in a single group is relevant in that context.
     
  13. paulsamuel Registered Senior Member

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    hold your horses. natural selection works at the level of the individual, whereas groups evolve. inclusive fitness explains altruistic acts, but there aren't really any altrusitic acts, there's always a mutual benefit.
     
  14. spuriousmonkey Banned Banned

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    I am thinking now about evolutionary stable strategies. I never really understood the concept so I might be making a mistake in my reasoning here, so please feel free to point it out to me.

    If 'grandparents' or other closely related senior family members can help spreading the genes of their offsprings offspring, than the reverse must also be a possibility. In fact, I would predict that the reverse tries to counteract the 'inclusive fitness' phenomenom.

    I predict for a ESS to emerge:
    Grandparents/senior couples will actively try to dminish the fitness of non-related junior couples still in their reproductive age and their offspring.

    I will put it now bluntly to make my point and problem clear:

    Why aren't grandparents actively involved in killing other peoples offspring?
     
  15. paulsamuel Registered Senior Member

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    don't know. i've heard of grandparents helping in the rearing of offspring's offspring, but have never heard of active murder. perhaps cost/benefit ratios are too high when they murder, and their ROI is higher when they merely help in rearing and maintaining maximum home range.
     
  16. Dr Lou Natic Unnecessary Surgeon Registered Senior Member

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    I've seen grandparents slandering other peoples grandchildren in talent contests and the like. Once upon a time this instinct may have been focussed on more aggressive activities.

    We probably developed the need for grandparents long before we were homo-sapiens. It was probably extremely vital at one stage. Like if you look at elephants, they need to survive for longer than most animals because an experienced old matriarch is vital for the survival of the herd. They need a member of the social group who knows where to find water in droughts and so on.
     
  17. BigBlueHead Great Tealnoggin! Registered Senior Member

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    I know that. I'm saying that if care was mutual across an entire population, that is, the same for every individual, then it would not represent a selective advantage for any individual. But, in this case, it's only mutual across a single social group, who probably come to be (at least somewhat) related to one another genetically over time.

    There are examples of altruistic acts that benefit the population and not the individual, although they generally require a resource-limited environment. (That is, when food is severely limited, an organism that consumes less food can coexist with a greater number of related individuals, although individually they'll be weaker. There's an example I was given in school of a species of insect that lives in pitcher plants during its larval instar, where this principle seemed to apply.)
     
  18. John Connellan Valued Senior Member

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    How do u define "altruistic" in the above sentence?
     
  19. paulsamuel Registered Senior Member

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    In the example above, then the prediction would be that altruism would not evolve at all. However, one must remember the "ghosts of evolution past." The behavioural ecology of a population or species can change over time due to mere stochastic vicissitudes. And so altruism can evolve under one mileau, and when that mileau changes, the "ghosts" of altruism remain. I suspect that's what happened in humans.

    I'd love more detail on the pitcher plant bug if you can remember.
     
  20. paulsamuel Registered Senior Member

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    i am using 'altruism' literally
     
  21. BigBlueHead Great Tealnoggin! Registered Senior Member

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    Whether humans exhibit altruistic behaviour is not clear to me; I am more inclined to believe that humans exhibit complex forms of learned cooperative behaviour, from which they demonstrably derive large benefits. However, I cannot prove this.

    This was an example from a biology class from several years ago, so I'm having trouble finding a reference. Apparently there are several different kinds of insect that pass their larval instar in pitcher plants - sarcophagid flies, pitcher plant mosquitoes, and so on.

    The idea was that a pitcher plant contained a very limited amount of protein for the larva to consume, since it had to come from the bodies of other insects that fell in. Assuming that the mother insect laid many eggs in the plant, and a large number of larvae could therefore hatch, we would expect in advance that "greedy" larvae would employ the strategy of consuming as much food as possible, thereby edging out their siblings who are naturally competitors.

    However, if a group of larvae all inherited a "non-greedy" trait from their parents, such that they only consumed as much food as was necessary for their development into adults, then more of these could survive in the same plant.

    The "greedy" insect, therefore, would be stronger and more able than the "non-greedy" insect, but fewer in number; weight of numbers might tip the scales in favour of the "non-greedy" insects, even though the fitness of individual "non-greedy" insects is lower.

    Thus, selection for altruistic behaviour is possible if it benefits the population, although this example has a very restricted environment and is sort of a special case.

    I'll see if I can find the example, but so far I haven't been able to.
     
  22. John Connellan Valued Senior Member

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    I am afraid that altruism, as defined by selflessness by an individual DOES occur in the wild. It is even an accepted behavioural ecology term!
     
  23. paulsamuel Registered Senior Member

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    So you say.

    Give me examples, I will give you the mutual benefits.

    Altruism in behavioural ecology is not really altruism because of mutual benefits. Behavioural ecologists know this. Now you can learn it, if you're able. Try reading Krebs and Davies, An Introduction to Behavioural Ecology, then get back to me.
     

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