Cells Repairing Themselves

By Sean Carroll | September 21, 2011 9:26 am

Speaking of self-repair, here’s a fascinating new finding from Malin Hernebring in Sweden. Here’s the technical paper, from a few years ago; it’s part of Hernebring’s Ph.D. thesis work. (Via Richard Dawkins’s site.)

As we age, our cells gradually decay; the DNA stays relatively intact, but proteins degrade with time. This is a big part of the aging process, leading to wrinkled skin as well as more serious consequences. When you think about it a bit, that raises a puzzle. A newborn baby arises out of the cells of its parents. So if the proteins simply decay without repair, every generation would get handed down a degraded set of proteins. At some point, therefore, there has to be some repair job, so that the baby gets fully functioning proteins.

If this idea is right, you might guess that the repairs happen at the level of ovum and sperm; maybe when these cells are created, extra effort goes into tuning up their proteins into working order. But the new research says no — it’s actually after conception that the clean-up crew arrives. The newly conceived embryo consists of stem cells that soon begin differentiating themselves into the different kind of mature cells. It turns out that it’s during this differentiation process that proteasomes go to work, breaking down the damaged proteins and generally tuning up the engine. (Maybe this is when the soul is implanted in the embryo?)

The next obvious question is: why can’t these cellular clean-up crews be active all the time? There are clear implications for studies of (and therapeutic approaches to) aging. Nature wants all the individual animal organisms to die, making room for new generations; but there’s no reason we have to go along with the plan.

CATEGORIZED UNDER: Science, Top Posts
  • Rick

    Along somewhat similar lines see:

    http://www.sciencedaily.com/releases/2011/09/110920163215.htm

    “Researchers have shown they can reverse the aging process for human adult stem cells, which are responsible for helping old or damaged tissues regenerate. The findings could lead to medical treatments that may repair a host of ailments that occur because of tissue damage as people age.”

    Now, if I can just hold on long enough ;)

  • David H.

    Cool research, but:
    “Nature wants all the individual animal organisms to die, making room for new generations”
    *cringe*
    The idea that we die for the good of the species (by making room for the youngins) isn’t really accurate. We die because nature doesn’t care. More precisely, nature has us live as long as needed to make babies, and after that, with allowances for raising said babies, it couldn’t care less. Any adaptation that let us live longer would have been wasting energy better spent baby-making.

  • anon

    “the DNA stays relatively intact, but proteins degrade with time”
    i dont think that quite right,
    proteins are continually recycled.
    as we age for each cell generation the DNA telomere gets continually shorter

  • Aaron

    I have to echo the *cringe*. Neither nature nor evolution is an agent, and it is rarely useful to model either as one. Products of evolution can be, and it can be extremely useful to talk about their wants (conscious or not) in terms of what has been successful.

  • H

    I think the cells are conserving energy and work by only revamping the cells that have made a baby instead of revamping every cell. Working smart instead of working hard.

  • BL

    Oh Science !

    I hope we find a cure to aging soon thanks to stem cell research. This disease touching 6.3 billion of the population is quite troublesome.

    Hopefully great people like Mr Aubrey De Gray will help change the minds about immortality and why we should cure aging.

  • Anchor

    “At some point, therefore, there has to be some repair job, so that the baby gets fully functioning proteins.”

    Where does one think the fresh proteins in offspring come from? From the parents? The genetic endowment in the DNA in the chromosomes code for manufacturing proteins from scratch (or from suitably simple molecules that aren’t complex enough to be easily damaged, such as amino acids). The ‘repair job’ is the act of reproduction itself: throw out the old, age-damaged and contaminated models (typically the female and male parents who have contributed their genetic heritage to the offspring) and start over again from the top, that is, from the least complex stage in the most compact possible package (the fertilized egg or its immediate antecedents) that contains all the information necessary to deploy a fully-functional adult. Repeat as often as opportunity and resources permit before age-related degradation prevents reproductive success.

    Death is a crucial function of life.

  • Mike

    Anchor,

    You say that “[d]eath is a crucial function of life.”

    But it doesn’t have to be, does it? Do you think there is some fundamental reason why we can’t come up with a repair job that doesn’t involve reproduction in the sense you describe, and death?

    One may have religious, moral, ethical or philosophical complaints — which I wouldn’t agree with anyway — but isn’t finding an alternative way to implement such repair “simply” a matter of gaining greater understanding and then engineering a solution?

  • Nullius in Verba

    ?!
    What percentage of the proteins (or even the DNA) in an adult human (or a newborn baby, for that matter) originate in the parents? And how did the marvellous Mother Nature squeeze them all into the gamete?

    According to the usual evolutionary thinking, the purpose of death is not to ‘make room’, nor does it lose interest after making babies. It’s a mechanism for resisting diseases and parasites. Pathogens usually have very short life cycles and so evolve and adapt rapidly to break our immune defences. We can’t keep up, with our much slower reproductive cycle, and can only build in so much protection. It’s like every cell in our bodies is set with a combination lock, that the immune system uses to tell friend from intruder. It only takes so long for the pathogens to search through all the combinations. And the body can’t change the combinations on all its cells simultaneously – there would be an awkward period part way through, where bits of the immune system and bits of the body had mismatched codes and would attack one another. So evolution achieves the effect by changing the combination in one cell and then throwing the rest of the body away – the one cell being multiplied to make a new body. It’s shockingly wasteful and inefficient, but effective. Better designs are no doubt possible, but not easy to evolve by blind exploration.

    You don’t want old and out-of-date models hanging around as they provide a reservoir for diseases – just as immunisation programmes have to cover a big enough proportion of the population or the unimmunised act as a reservoir for new epidemics. Hence death is to some extent programmed in.

    If we were to somehow engineer our immune systems to eliminate all disease, then immortality would evenually evolve naturally. (Continuing to have babies is more efficient than taking a 16-year break every generation to grow a new body.) Conversely, if we turn off aging and death without first dealing with disease, we will face ever-more-precisely adapted plagues that circumvent all our defences, one by one. It’s like the story of antibiotic-resistance – it would start off as a miracle story to banish death forever, until you realise that over-use has shortened its time of effectiveness, and ‘forever’ isn’t as long as you thought. You have to keep moving.

    Rejuvenating cells is certainly a useful trick to know, and undoubtedly will be part of the ultimate solution. But a better trick would be to be able to switch immune system recognition signals smoothly, mid-life.

  • Burned

    @6: Oh, he’s called Aubrey, now, is he?

  • Anchor

    @#8 Mike: “Do you think there is some fundamental reason why we can’t come up with a repair job that doesn’t involve reproduction in the sense you describe, and death?”

    No. Does the sense of what I describe suggest that I think we can’t?

    “One may have religious, moral, ethical or philosophical complaints — which I wouldn’t agree with anyway — but isn’t finding an alternative way to implement such repair “simply” a matter of gaining greater understanding and then engineering a solution?”

    Sure. Why not? (Without the slightest religious, moral, ethical or philosophical compunctions, even if I did see any relevance in applying those arbitrary filters when mentioning the D-word).

    There’s an encouraging difference between how nature does something and how human ingenuity (which one must acknowledge ultimately is a product of natural selection) can be brought to bear on a problem. While nature doesn’t care about generating or maintaining organized complexity, humans can at least recognize a ‘problem’ or a shortcoming in the natural means that may be addressed by alternative solutions. Nature doesn’t have to worry about it, but we can. We have a stake in being alive.

    Nevertheless. It is easy to see that life and evolution has depended on death and extinction. That IS how organized complexity in matter has emerged naturally. A thermodynamic opportunity (survival of a given complex configuration) presents itself in the ‘systematic rejection’ of faulty parts or in throwing out the trash. A potential niche becomes vacant. It tends to get filled. Recycling the broken bits in the form of useful raw material for the support of existing living systems enters into the scheme, to be sure. But it takes effort to segregate the signal from the noise, and however one cuts it (what’s essential from what’s not in terms of order) under the dispassionate glare of entropy, ‘death’ by any other name will remain a fact of life.

  • Mike

    Anchor,

    Thanks for the response. I agree that natural selection is how organized complexity in matter has emerged naturally. Not sure that bringing the ultimate arbiter entropy into the picture is meaningful in any practical sense. As for me, I’m only looking for a little progress in the very near future. ;)

  • Anchor

    “Not sure that bringing the ultimate arbiter entropy into the picture is meaningful in any practical sense.”

    No “practical” sense implied in the meaning, I assure you. ;)

    Just saying that whatever we may do to mitigate aging or delay death, our solutions will inevitably have to comply with natural laws, and that circumstance must continue to satisfy the appetite of entropy. If there is any meaning to be had at all, I submit it is there.

  • Eric Habegger

    I am beginning to see an interesting convergence between biology and physics. A prediction can be made that the zeitgeist of the 21st century will be one where unusual sychronicities will begin appearing between biological processes and physics processes. Certainly this process of organism regeneration may have interesting correlations with a so called “bouncing universe”. I’m not thinking so much about the means, proteasomes, as with an overarching structure of death, regeneration, and recycling of an existing universe into a new baby universe. (Not at all thinking multiverses here. Hate the concept.)

    For instance one could think of differentiation of cellular structure through stem cells as similar to differentiation of fields, forces, dimensions, and ultimately particles through asymptotic freedom in the early condensed state of the universe. Gradually these are pared away as the organism grows. Internal dependencies between biological structures then start manifesting themselves just as internal dependencies in solid-state physics manifests themselves as the universe cools and expands. At some very late stage in the development of the organism or universe everything will have become interdependent and there will be no excess material remaining for regeneration and the organism and the universe collapse, or bounce, into something new. ( and hopefully improved). :-)

  • Charlie

    “Nature wants all the individual animal organisms to die, making room for new generations…”

    Lets be a little more scientific here. Nature doesn’t care. Natural Selection also doesn’t care about extending your life (beyond a certain point) because you are probably already dead from a predator (by a certain point) so there is not much gain in fitness for extending your life past that point.

    Comments above that suggest that there is “selection for” death should provide a reference. It is certainly not “easy to see” or the mainstream viewpoint of those that study evolution.

  • BrianDennehy

    Really great post that, Nullius in Verba, thanks!

  • Anchor

    “Comments above that suggest that there is “selection for” death…”

    Where is this suggestion?

    “It is certainly not “easy to see” or the mainstream viewpoint of those that study evolution.”

    Considering that the suggestion doesn’t exist and a false context is placed in its stead, its even easier to see how some people seem to prefer to make things up rather than read carefully.

  • Brian Too

    As I understand it, cancer has been one of the monsters stalking efforts at extending life.

    @2. David H.,

    So all we have to do then, is to continue making babies beyond the usual biological timeframes? In fact indefinitely!
    ;-)

    Of course even it works, we are then faced with the problem of what to do with all those babies. In a world where their ancestors are not going to their, er, greater reward?
    Soylent Green anyone?
    :-(

  • http://thefloatinglantern.wordpress.com Tim Martin

    So new cells in our bodies (the ones we’re making all the time) don’t get made using new proteins? Why not??

  • http://vacua.blogspot.com Jim Harrison

    Heck, depending on how you decide who I am, I’ve been alive for three billion years or so, though I admit it gets pretty dicey passing through all those microscopic phases.

  • AI

    Of course there is selection for timely death, it’s due to limitation of resources and evolutionary arms race. Lifespan of all organisms is carefully tuned and linked to reproductive lifespan.

    Due to natural selection each new generation is in general better adapted then the last one. It follows that once new generation is sexually mature it is better for it to take over the task of producing offspring from the last one (to ensure adaptation is as fast as possible). Keeping the old generation fertile for much longer would be counterproductive.

    On the other hand keeping infertile individuals alive only makes sense if they can provide some benefit to the group which outweighs the cost of resources they consume, this may be for example helping with caring for the young and passing knowledge to them but eventually that job is also over (as new generation of elders comes along) and by that time they should die. If they were to keep on living they would imperil their own offspring.

    Aging also serves its purpose – it is a great mechanism to ensure that in times of stress (limited resources, predators, etc) it is those old individuals who will die first, this prevents them from outcompeting the younger generations.

  • Mike

    AI,

    Your view seems to be based on two incorrect assumptions:

    1. Humans may figure out the very complicated process of prolonging lifespans, but will not figure out to implement favorable adaptations, perhaps even better than through natural selection.

    2. Humans living longer create mainly problems for society, imperiling offspring, using scarce resources and the like. Why isn’t the opposite the more likely outcome. What’s to stop it from happening? Not the laws of physics, but merely our current lack of understanding.

  • Low Math, Meekly Interacting

    There’s repair at every level, molecular, cellular, tissue, system. DNA seems “stable” because there are active repair mechanisms at work all the time. Probably because the chemical structure of protein is so much more complex, and because no redundant copy of information about correct protein sequence exists outside of DNA, it’s a lot more feasible to simply destroy a protein and start from scratch than it is to repair it. This process happens all the time quite independently of aging. It’s an integral part of the cell’s many quality-control mechanisms, and even serves a very immediate regulatory roll. For instance, proteins that are no longer needed are actively targeted for destruction. Some proteins are even generated at a constitutive rate only to be chewed up on the proteasome within seconds so as to prime the cell for a hair-trigger response to specific stimuli, such as changes in the partial pressure of oxygen. Those cellular cleanup crews ARE active all the time. And by that I mean All. The. Time. Not a single protein gets synthesized without the proteasome standing in a sate of constant vigilance, ready to chew it to bits if it comes out wrong. All but the most quiescent of cells are constantly building proteins and breaking them down, and, again, this unremitting activity serves a variety of needs. If only anti-aging could be so easy.

    I think there’s a LOT more to aging than old proteins hanging around. Steady loss of telomeric sequence and accumulated somatic mutations play a big roll in the degradation of correct protein synthesis and quality control as cells approach senescence. In very few cells and tissues is there no turnover. In fact, in most tissues, excepting very mitotically quiescent organs like the lens of the eye, the brain, the heart, there’s constant cellular turnover. That process requires constant remodeling of the extracellular matrix which virtually all cells outside of the circulatory system are in constant contact with. In fact, cells find it difficult to divide and migrate without burrowing through the protein matrix that they’re embedded in, and then having it be repaired in their wake.

    All of this gets stuff gets creakier as we get older. It’s entropy, plain and simple, and it’s a ubiquitous problem. I hate to be a reflexive naysayer, but I find the notion that ramping up proteasomal activity would somehow reverse, or even slow, the aging process is way, way too optimistic.

  • David H.

    So, I was being flippant with my earlier remark, I’m aware there’s still a lot of uncertainty regarding the role of aging. Nevertheless, I’m going to reiterate my skepticism for any theory of aging that claims it is an altruistic adaptation, adopted for the good of the species. Even the most ardent group-selectionist would raise an eyebrow at this claim. Keep in mind, evolution of altruistic traits is hard under any circumstance, and is constantly fighting against evolutionary pressure to be selfish. Could altruistic death evolve under some circumstances? Sure, and in fact, there are plenty of such cases. But aging is nearly universal among animals; for it to be altruistic, we’d need some kind of group selection operating on nearly every animal species on the planet. Take an example of extraordinarily successful altruism: multicellularity. Even here, selfish selection crops up routinely as cancer. And yet we don’t see methuseleh variants of organisms taking over and destroying entire species in the same way.

    Nullius in Verba – Your model is interesting, I’ve never heard of it before, do you have any references? Infectious disease has been an important selection pressure on animals, and is probably critical to the evolution of sex, but I don’t see it being that useful a pressure to evolve aging, mainly for the reasons above.

    AI – What you’re proposing is a classic example of group selection that just doesn’t work. Group selection only works when competition between groups overwhelms competition within groups. The advantage to an organism which cheated, and avoided dying to produce more offspring, or avoided dying off during famine would be tremendous, whereas the advantage to others provided by its dying would be spread over its children and every other organism in the population. A lot of this was covered a while ago, by GC Williams among others.

  • Low Math, Meekly Interacting

    Everything points to this evolutionary truth: The fate of all multicellular organisms with proliferating cells is in either death by senescence or death by cancer. Natural selection insures it. All multicellular life has evolved to destroy cells that proliferate uncontrollably. If and when this check finally breaks down, cancer will claim the organism. Why? Because proliferating cells in the body evolve. Those that grow the fastest, furthest, and can gather resources the most successfully to those ends, will dominate. Hence, unless the whole organism goes down, cancer is an inevitability. The trick is to make the organism last long enough to reproduce before cancer or senescence claim it. All that is certain is that all multicellular life has adapted highly-conserved strategies to maintain this balance. In terms of the individual, nothing else matters from a reproductive and evolutionary standpoint.

    So the fact that some organisms can live well past their reproductive stage is a bit of a mystery. Benefits conferred to younger generations is one plausible explanation, but far from iron-clad.

  • Low Math, Meekly Interacting

    Believe you me: I loves me a little bio-talk in a physics forum, and hate to go OT. But this supraluminal neutrino thing is blowing my desperately hopeful, probably gullible little mind. This is crying out like bloody murder for a reality check in a forum like this blog…just sayin’…

  • Plank

    @ Low Math, haha, indeed – checked here to read about those FTL neutrinos and ended up with this!

    Great stuff though – I don’t fancy dying at all if I can avoid it. At the very least, id like to be in possession of all my faculties until as near as possible to the end. If this kind of research can improve quality of life, I’m all for that.

  • http://www.physorg.com/news/2011-09-cern-faster-than-light-particle.html thales

    Agreed on the FTL neutrinos.

    My favorite speculation so far: Perhaps it has a small probability of temporarily existing at a velocity slightly greater than the speed of light (or goes back in time, same thing I think) via some sort of quantum fluctuation in where its already tiny mass can temporarily become slightly negative or even imaginary.

    (HT to commenter jsberry at physorg.com)

  • Low Math, Meekly Interacting

    Ahhh! I don’t want to hijack, just didn’t know where else to bring it up!

  • Count Iblis

    There is some evidence that the body uses vitamin in D to switch on many different processes involved in properly maintaining the body:

    T cells only activate when they are exposed to vitamin D

    vitamin D stimulates gingival cells and lung cells to produce a natural antibiotic

    And there has been a lot more results like this that show that vtamin D is involved in regulating processes that maintain the body, from regulating the immune system to building muscles etc.

    This suggests that even these basic self-maintainance activities are considered to be luxery, the body will cut back on them if vitamin D levels are low. Presumably, the body uses vitamin D as an indicator for the availability of food. Our ancestors would have had lower vitamin D levels in the Fall. Precisely at that time it would make sense to cut back on energy use to build up fat reserves for the coming Winter.

    It could thus be that a body that doesn’t age would need to expend a huge amount of energy in mantainance costs. You would be eating and sleeping all day long without being able to do any physics.

  • AI

    David H: “AI – What you’re proposing is a classic example of group selection that just doesn’t work. Group selection only works when competition between groups overwhelms competition within groups. The advantage to an organism which cheated, and avoided dying to produce more offspring, or avoided dying off during famine would be tremendous, whereas the advantage to others provided by its dying would be spread over its children and every other organism in the population….”

    First of all the claim that “group selection only works when competition between groups overwhelms competition within groups” is patently absurd. Wherever there is competition there is selection, selection works on all levels all the time, there is no “either or” here.

    What’s more in the case of animals which depend on the group for their survival evolutionary resilience of the whole group is always far more important then relative success of any individual within the group (measured as the number of offspring produced relative to his peers). If the group goes extinct all it’s members go extinct with it, how they compared among themselves is completely irrelevant at this point.

    As for your counterexamples, the part about famine makes no sense whatsoever (did i claim dying to famine is beneficial?). As for the number of offspring, when producing more offspring is beneficial organisms simply produce more offspring, they don’t have to live longer to do it. Lifespan is all about the speed of evolution, longer lifespan means slower adaptation and is therefore not beneficial.

    For example let’s say you start with 2 otherwise identical groups, A and B, which differ in that individuals in group A live 10 times longer then those in group B, the number of offspring per lifetime is the same in both groups. Group B will of course outcompete group A since it can evolve new adaptations 10 times faster (group B produces 10 generations in time it takes group A to produce one).

  • ChicagoSpaceMan

    Low Math, Meekly Interacting great post, learned a lot!! Such a rich,beautiful system life is!

  • David H.

    AI –
    To address your points:
    1. “selection works on all levels all the time” – indeed it does. But selection pressures at different levels can be in conflict, especially for altruistic adaptations, which by definition are detrimental to the individual. For group altruism to evolve, the benefit to the group must outweigh this cost to the individual. Sometimes this happens, emphasis on “sometimes”. But even biologists who support group selection agree that this is not common.
    2. “resilience of the whole group is always far more important then relative success of any individual within the group” – again, yes, sometimes, but not often, and only in strongly social species. Aging is nearly universal, it occurs in herd animals and lone predators, autotrophs and heterotrophs; why is it maintained in all these non-social species?
    3. “did I claim dying to famine is beneficial?” – I’m not sure how else to interpret your previous statement: “it is a great mechanism to ensure that in times of stress (limited resources…) it is those old individuals who will die first, this prevents them from outcompeting the younger generations”. What else is a time of stress involving limited resources?
    4. “Lifespan is all about the speed of evolution, longer lifespan means slower adaptation and is therefore not beneficial” – No, lower rates of reproduction means slower adaptation: fewer offspring, fewer new variants for selection to test. A longer lifespan at the same rate of reproduction would be beneficial, allowing more total offspring. It’s detrimental only if it is linked to lower fertility; this is GC Williams “Antagonistic Pleiotropy.” If every extra year of life requires fewer offspring per year, then nature will select shorter lifespans and more offspring. But this is selection at the level of individuals (because energy spent keeping alive is energy not spent making babies, or longer life can only come at the cost of delayed sexual maturity, etc), and is maximizing individuals’, not group, fitness. Your example is a perfect illustration: group B reproduces 10 times as fast as group A. It doesn’t only evolve faster, it just plain old outcompetes A; if groups A and B were mixed, B’s would still win, they are more fit individuals.

    Look, this isn’t an ideal place for substantial scientific debate, and your theory is something that people did subscribe to in the past. I suggested reading up on, or about, GC Williams, who was one of the first to explain these issues. I also suggest checking out this post from DS Wilson, one of the premier evolutionary biologists who studies group selection, where he describes the problem with naïve group selectionism: http://scienceblogs.com/evolution/2009/10/truth_and_reconciliation_for_g_1.php (in fact, I recommend the entire series). But who knows, I could be wrong; I’ll repeat what I asked of Nullius in Verba – I’d love to see references to your theory that explain it in detail and discuss the supporting evidence.

    -David

  • AI

    David: 1. “selection works on all levels all the time” – indeed it does. But selection pressures at different levels can be in conflict, especially for altruistic adaptations, which by definition are detrimental to the individual. For group altruism to evolve, the benefit to the group must outweigh this cost to the individual.

    Well, this is obvious, I don’t see how it contradicts anything I said.

    David: 2. “resilience of the whole group is always far more important then relative success of any individual within the group” – again, yes, sometimes, but not often, and only in strongly social species. Aging is nearly universal, it occurs in herd animals and lone predators, autotrophs and heterotrophs; why is it maintained in all these non-social species?

    The reason has to do with competing with one’s own offspring. But let’s stick to lifespan for now, this is a simpler case, and even there you don’t seem to understand my argument.

    David: 3. “did I claim dying to famine is beneficial?” – I’m not sure how else to interpret your previous statement: “it is a great mechanism to ensure that in times of stress (limited resources…) it is those old individuals who will die first, this prevents them from outcompeting the younger generations”. What else is a time of stress involving limited resources?

    Yes, but again that was about aging, not lifespan, you switch between the two as if they are the same thing, but they are not, there are different reasons behind each. The part you quote wasn’t stating that dying to famine is beneficial, only that when a certain % of population is to die, it is better if it’s the older generations who die. That much is even hardcoded in our own instinct, parents often prefer to die in place of their kids.

    David: 4. “Lifespan is all about the speed of evolution, longer lifespan means slower adaptation and is therefore not beneficial” – No, lower rates of reproduction means slower adaptation: fewer offspring, fewer new variants for selection to test.

    Testing new variants is not adaptation, adaptation is about spreading them, you want more generations to amplify new beneficial trait and mix it with other beneficial traits (many of which will not be present in the original “inventor”) , this cannot be achieved by one individual (especially the latter part which is critically important for genetic diversity and therefore population health).

    David: A longer lifespan at the same rate of reproduction would be beneficial, allowing more total offspring.

    First of all you are assuming that more offspring equals success, but this is obviously wrong. Why do you think twins are so rare and multiplets even rarer? From biological perspective it’s trivial to produce them. It’s successful offspring that count, and producing too many offspring can lower the chances of success of them all.

    More generations always beats more offspring.

    David: It’s detrimental only if it is linked to lower fertility; this is GC Williams “Antagonistic Pleiotropy.”

    Look, I don’t appreciate arguments from authority, but even GC Williams knew that group selection does work for closely related individuals and that’s more then enough to support my argument.

    David: “If every extra year of life requires fewer offspring per year…”

    Sorry, but what does that even mean?

    David: Your example is a perfect illustration: group B reproduces 10 times as fast as group A. It doesn’t only evolve faster, it just plain old outcompetes A; if groups A and B were mixed, B’s would still win, they are more fit individuals.

    But it outcompetes A precisely because it evolves faster! At the start they are equally well adapted, and their population numbers are exactly the same. B don’t start more fit, they eventually win precisely because they adapt faster due to shorter life cycle!

    Sorry but the above is the most important part here and it cannot be explained more clearly, if you don’t get this example then I don’t think I can help.

    David: Look, this isn’t an ideal place for substantial scientific debate, and your theory is something that people did subscribe to in the past. I suggested reading up on, or about, GC Williams, who was one of the first to explain these issues. I also suggest checking out this post from DS Wilson, one of the premier evolutionary biologists who studies group selection…

    This is as good a place as any. As for the latter I don’t much care about current fads and sociology of the field, selection works on all levels, even GC Williams knew that much even though he built his career on questioning it’s relative importance.

    You have yet to articulate any valid counter argument to my example, saying that it’s a group selection and some people think group selection is unimportant does not count as a valid counter argument.

    Finally my point is valid even in terms of individual selection, as long as you define “evolutionary success” properly and not by such simplistic measures as number off offspring. For example if you define success as the percentage of population gene pool that can be traced back to a given individual over a long period of time, then you will arrive at the same conclusions – in general it is better to amplify beneficial traits through many short generations then through one individual dominating the gene pool which makes the whole population (his offspring included) more vulnerable through depletion of genetic variety.

    If the population goes extinct the individual success of all it’s members is null.

    David: I’d love to see references to your theory that explain it in detail and discuss the supporting evidence.

    The theory in question is the theory of evolution, my statements and examples concerning lifespan follow directly from it.

  • Realist1953

    (Maybe this is when the soul is implanted in the embryo?)
    **********
    WHAT? What “soul”? How DARE you put something totally religious (and as valid as thinking there is a Mars, “god of war’) into an article about SCIENCE.

  • David H.

    Ok, I’m mostly done here, but to focus on your model for a second: A organisms have 10 times the lifespan of B organisms, each produce the same # of offspring per lifetime, so if we say that # is 10 offspring and A’s live for 10 years, then on average, A’s produce 1 offspring per year for 10 years and B’s produce 10 offspring per year for 1 year. In a mixed population of, say, 10 A’s and 10 B’s, all young so they have their entire lifespan ahead of them, in a year there will be 10 new A’s and 100 new B’s, while all the old A’s are still around but all the old B’s die. Now we have 20 A’s and 100 B’s. Repeat, and the next year you have 40 A’s and 1000 B’s. It gets worse from there, B’s are much more fit, because they grow faster, this isn’t even evolution, it’s simple population dynamics.

    As for the rest, we’re just circling each other. I’ve explained group selection for altruism only works under special conditions, and I’ve yet to see any explanation for why those conditions would hold for nearly every animal on the planet. I’m honest about my request for a reference, by necessity your argument is short here, and if it so clearly follows from the basics of evolution, then there should be a paper out there that explains it in detail. I’ll be glad to be proven wrong. And if there is no such paper, but you think the answer is so clear, then there’s a golden opportunity: write something up, upend our current understanding of aging and lifespan, earn scientific immortality.

    Ok, that’s all. I’d love to see a reference, but otherwise I think we’re done here.
    -david

  • AI

    I’m glad that you agree that B are much more fit due to shorter lifecycle, but your analysis makes one very unrealistic assumption – that environment can support any number of organisms A and B.

    The assumption in my analysis (which i should have made explicit) was that an environment can only support a certain number of organisms A and B (the way they are at the start of experiment) at the same time and it is already saturated with them at the start of the experiment. This is a much more realistic case and this is when speed of adaptation is what matters most since it’s the only way for A and B to increase their numbers. For example an adaptation may allow them to utilize resources more efficiently, or give them access to new areas, or make them better at avoiding predators, etc, all ways to increase environmental capacity.

    As for the reference, sorry, I can’t help you, but you are free to develop these ideas and publish them yourself if you so desire, scientific immortality awaits ;)

  • http://trollvalhalla.com Anti-nerd

    UH UH

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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