Help! questions regarding evolution from a layman.

Discussion in 'Science & Society' started by semberardens, Aug 11, 2012.

  1. Randwolf Ignorance killed the cat Valued Senior Member

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    No. Any advantageous mutation, no matter how minute the difference might first appear could lead to conservation of the genes responsible. Therefore, this should increase the survival rates for the offspring albeit very slowly and over a long period of time. However, if there was no difference AT ALL between the first mutated animal and the rest it wouldn't have any advantage, by definition.
     
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  3. billvon Valued Senior Member

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    If, practically speaking, the mutation produced no difference in the animal, then that trait would not be propagated.

    If, practically speaking, the mutation produced a slight benefit in survival/fertility, then that trait would spread throughout the gene pool.
     
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  5. semberardens Registered Member

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    Thanks, I guess that answers that. do we have any examples of beneficial mutations amongst animals today ?
     
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  7. Fraggle Rocker Staff Member

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    By the time H. sapiens arrived in Europe, the ice age which has now almost ended (the permanent glaciers and polar icecaps may very well disappear by 2200) was already waning. The weather was not as cold so they did not need the shorter, heat-conserving limbs of the Neanderthals. Smaller, faster, nimbler prey animals (warmer-weather animals like us) were migrating northward at the same time. Hunting them required different physical abilities in an obligate carnivore (none of the recent human and near-human species had the gut to support a bacterial culture for digesting raw plant tissue, and cooking fires are a very recent technology) than the ponderous, fat-shrouded woolly mammoths, woolly rhinos, aurochs, cave bears, etc.

    It's likely that the articulation of the Neanderthal frame would have made it difficult for them to use a bow and arrow. They were not buoyant so capturing fish in the warmer waters would have been hard for them.

    Our species was adapted to the warming European climate before we even got there. The Neanderthals might have adapted through evolution, but before they had the chance we came in and marginalized them. They did not die off, but simply interbred with the more successful, more prolific species. People of ancient European ancestry still have about 5% Neanderthal DNA.
     
  8. semberardens Registered Member

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  9. Yazata Valued Senior Member

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    Evolution doesn't necessarily work in terms of very small changes.

    There are two biological terms that are useful here: genotype and phenotype. Genotype refers to an organism's heritable genetic makeup on the level of DNA. Phenotype refers to an organism's biochemistry and anatomy.

    The mutations that drive evolution happen down on the genomic level. The "very small changes" that you are thinking about are very small differences in anatomy.

    So what we need to think about is how changes in the genome come to be expressed phenotypically.

    This is one of the cutting-edge areas of evolutionary biology at the present time. It's often referred to as "evo-devo" by biologists, referring to the merging together of 'evolution' and 'developmental biology'.

    There's a very readable explanation of evo-devo on this website:

    http://evolution.berkeley.edu/evolibrary/article/evodevo_01

    Right, excellent questions.

    The point to take away from this "evo-devo" stuff is that the heritable changes that are passed along from generation to generation in evolution are genomic changes in the DNA code. These kind of changes will often express themselves in the course of fetal development. Even small changes in how fetuses develop can lead to sudden and occasionally very dramatic differences in adult morphology and phenotype. (Imagine that a mutation deletes the 'stop' command for the growth of a particular body part.) And finally, natural selection operates on the resulting adult forms, assuming that they survive, in terms of how successful they are in reproducing and passing along their new gene variants to subsequent generations.

    In other words, it's probably a mistake to think of evolution taking place in terms of infinitesimal differences in phenotypic specifications such as arm length or skin color. It's perfectly reasonable to question whether such an infinitesimal difference would make any evolutionary difference at all in terms of natural selection. So your question is very good and it's one the evolutionary biologists have been asking and thinking about themselves.
     
  10. Cavalier Knight of the Opinion Registered Senior Member

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    157

    The difference is practical, but it is a statistical advantage only. In any one individual you may not even notice the difference if it is below our "threshold of perception," but that doesn't render it non-existent. Each individual then also suffers from a high variance in his or her actual productivity (which can further hide the impact of the beneficial mutation). Over long periods of time though, the advantage will be borne out, as the Law of Large Numbers begins to take hold, the (actual) average result will tend to the (statistical) expected result, which is that the reproductive rate of the mutant population will be 0.3% higher than that of the other part of the population.

    With all else held constant, over time, the tiny 0.3% difference will cause the part of the population with the mutation to grow faster than the unmutated population, and eventually to be more numerous than them.
     
  11. Aqueous Id flat Earth skeptic Valued Senior Member

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    semberardens,

    I don't mean to dog you, but even if it's right to connect Neanderthals to heat retention, I think this only favors them later in France. It may have nothing to do with why they evolved in the first place (600 kYA?)

    Think of what I'm saying this way: presumably the evolution of Neanderthals was complete by the time they were using animal skins for warmth. You see the issue I'm raising? It seems that Neaderthals appeared after an ice age (the Calabrian), not at the beginning of one. (Incidentally the magnetic poles switched around the time the Neanderthals emerged [sci-fi theremin plays here]).

    The best answer to your question requires us to guess about how we and they diverged from the presumed common ancestor. This divergence could have taken place anywhere, even in or near the tropics. We would have to try to guess what may have led to a Neanderthal branch. If I were to give you my best top 10 guesses, somewhere near the top I would list "whatever killed off the common ancestor". Was it the end of the glaciation? Disease? Some challenge to intelligence? Something eliminated the antecessor, but the Neanderthals mutated out and lived on. Something eliminated the antecessor, but our phenotype mutated out and lived on. What was it? Brain size and speech seem to be big contenders, but why? What possible pressure was fatal to the antecessor simply because of less intelligence and/or less speech? You might try to model this by asking what would (tool-making) apes be susceptible to that humans can avoid by reasoning? Drought? Starvation? Perhaps the ability to track prey was the reason for the success of Neanderthals back then when the "first mutation" appeared. Who knows? What is certain is that we gained brainpower. Neanderthals may be the only other hominid that comes close to ours.

    Incidentally, a crucial problem that comes with a large skull is that the birth canal has to simultaneously undergo selection. Presumably a vast number of antecessor mothers had to die in childbirth to select for a birth canal, which is "just barely" large enough. (Hence, labor today is severe and mother and child can still experience life-threatening trauma.) Suppose the barrel-shaped Neanderthal body style is a trait that allows the selection of larger birth canals in some more complicated way. All we can do is guess, but I don't think using furs later in their era necessarily has anything to do with surpassing the qualities of the antecessor. You see where I'm headed here?

    By the way, the small changes you are referring to can easily be compared to the (just for sake of argument) "silly millimeter" that allows the larger brain case to pass, or else kills both Baby Brainiac and his "slightly wider" momma. It can appear to you to be a physically small adaptation, and it can even be genetically small. Yet, with just a little flexibility in the pelvis, a softening of the infant's skull and ouila! You get a kid who may be able to track deer (or whatever problem was crucial). (BTW tools were already in use.)

    Think about it. This is a coordination between (a) pelvic "clearance" (b) size and flexibility of the skull (the hole on babies' heads - the soft skull is compressible, and addresses this problem) and (c) the pelvis that supports upright posture (it's narrower!). I mention the upright posture because we would have to guess that this is a concurrent upgrade to the phenotye that presumably solved some adaptation problem. But what? Chasing animals? It's an idea that's at least compatible with the cave paintings our low-brow cousins left us on their cave walls. (Of course I'm still just wildly speculating.)

    Here is some more discussion on bipedalism and the birth canal. Put this in your pipe and smoke it, and see if you can understand why the thermal thing doesn't have to mean that much. Being born, eating (and not being eaten) are maybe even more crucial than staying warm.

    After you've waded through the issues I'm raising, also consider this. The evolutionary race between our antecessor, the Neanderthals and us is only one of, say, maybe a dozen or two that raise the same kind of questions: what selects for any single hominid phenotype over its ancestral forms?

    It's all very mind boggling, but certainly a great topic, even if we're just bumping our gums.
     
  12. Fraggle Rocker Staff Member

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    The ramifications of the conflict between our uniquely massive brain and our bipedal locomotion are numerous.

    First off, simply evolving a wider pelvis, allowing a wider birth canal, would be impractical. Every time we take a step we have to transfer 100% of our body weight all the way from one leg and foot to the other. The muscles, bones and other tissues in our legs are already considerably modified from those in the other primates. Our gluteus maximus has actually been re-routed to help us lock our knees and stand erect: that gigantic double-half-moon shape we usually refer to as our "butt." If our hips were any further apart, the rocking couple resulting from the massive energy transfer would make our locomotion too ponderous and burn up too many calories. We'd need more food but we'd be too slow and clumsy to catch it. A regression to herbivory would be impractical: a gut large enough to maintain the bacterial culture needed to digest that much cellulose would be impossible for a bipedal grazer to support.

    Secondly, in order to wedge our heads through the birth canal, our babies are born with the most undeveloped brain of any placental mammal. Newborn giraffes literally hit the ground running. Even newborn dogs and cats, relatively helpless like most baby carnivores, can walk within a few weeks. Our babies are totally helpless for months, can't walk for a year, nurse for longer than that, and require a decade and a half of intensive parenting. (Whales mature in two years and even elephants take only five.)

    This has a second-order ramification of its own. No female animal can devote the majority of her attention and effort to raising and protecting her young, for more than a short time. So humans, by instinct, are one of the very few species in which both parents participate in childrearing, and in fact the entire "pack" tends to care for their young communally. One of the telltales of this adaptation is that humans are one of very few species in which the females are physically capable of copulation outside of their estrus cycle. (Some other ape species have this, as well as many dolphins.) The ability of a mother to satisfy her mate's cravings (even when pregnant or nursing) helps keep him at home where he can share the childrearing duties. In addition, humans are one of the very few species that live considerably longer than their childbearing years: we elders help our children raise our grandchildren.

    All because of the conflict between bipedal walking and an enormous brain.
    The discovery of Ardipithecus helped answer this question. Ardi was a transitional species that still had one prehensile toe and could take to the trees for safety, yet her (AFAIK only a female fossil has been discovered) articulation shows that she was fully bipedal. And she was still a grazing herbivore. It's suggested that the advantage of bipedal locomotion was simply that it left the creature's hands free to carry food back to the rest of the pack, allowing the mothers and children to remain in safety, increasing the survivability of the species.

    P.S. Ardi also solved the riddle over where bipedalism developed. It was in the forest, not on the savannah.
     
  13. spidergoat Liddle' Dick Tater Valued Senior Member

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    In human beings, many people can now digest lactose into adulthood, a feature not shared with most other mammals, who lose this ability after weaning. This mutation coincided with the rise of domestic animals that people could milk.
     
  14. billvon Valued Senior Member

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    An interesting one is the LDL-receptor–related protein 5 mutation. When the LRP5 gene has a very specific mutation humans develop much higher bone density. They discovered this mutation in someone who had a pretty serious car accident and walked away with no broken bones. It was prevalent in his family, and researchers discovered that no one in that family with the mutation had ever broken a bone. They are looking at it now to see if it can shed some light on treatments for osteoporosis. It has a few minor negative effects like parasitic bony growths in odd places (like the roof of the mouth.)
     
  15. MRC_Hans Skeptic Registered Senior Member

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    Short stature does not equal better heat retention. To retain agility, shorter people are generally smaller, not just smaller. Your surface area is proportional to the square of your size, whereas your volume is proportional to the cube of your size. So the larger you are, the better your surface/volume ratio becomes, heat-retention wise.

    - And as others mention, there are a number of other factors that determine hight.

    Temperature is not the determining factor, sun is. The dry inland climate gives you a lot of sun.

    Who says it must be small enough to be negligible? We can observe obvious individual variations in most kinds of populations. Those with a survival value will be favored by evolution.

    Hans

    (The killing will depend on your reaction to the answers

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  16. Fraggle Rocker Staff Member

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    This is an instance of neoteny, the perseverence of characteristics of infancy into adulthood. All mammals have to be able to digest milk as infants because it's their only source of nutrition. But their ability to synthesize lactase (the enzyme that breaks down lactose) attenuates as they grow older because after they're weaned milk has zero presence in their diet. In cultures that experimented with dairy farming (which is 1000% more productive use of grazing land than meat farming and therefore very useful as human population density increases), people who retained their ability to generate lactase had a survival advantage. This was a strong selection criterion, since older children who could not drink milk were more likely to die of protein deficiency before reaching puberty and passing on their DNA.

    We also see neoteny selected for in the "unnatural selection" of our companion species, the dog. (To be precise, a subspecies of wolf, Canis lupus familiaris.) Wolf pups are gregarious and playful, bark and wag their tails, but these traits vanish in adulthood. These are precisely the traits that endear dogs to us (as well as making them useful companions, nobody wants a dog who won't play with their children and isn't comfortable in a large mixed-species "pack"), so the individuals who retained them into adulthood were more likely to be kept around the hearth and allowed to breed. Today all dogs behave this way until their dying day.

    Even domestic cats display a bit of neoteny. By carrying them around, feeding them, and cuddling with them, we are impersonating their mother, and this triggers a reversion to kitten behavior.
     
  17. semberardens Registered Member

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    Actually there is a solution to the contradiction between pressure to be bipedal and pressure for a wider pelvis.

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  18. Fraggle Rocker Staff Member

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    A spherical skull is better than oblong for at least a couple of reasons:
    • Protection. A sphere is more resilient to blows than any other shape.
    • Efficiency. The physical neural paths should be as short as possible to maximize the speed of cognitive processes.
    • Cooling. The brain uses a significant portion of our energy and therefore generates a significant portion of our waste heat. Shortening the neural paths should minimize the energy usage and the waste heat.
    • Second-order effects. For example, an oblong skull would probably require greater blood flow for cooling, and therefore a larger heart to pump it.
     
  19. iceaura Valued Senior Member

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    Ardi was not a grazing herbivore.

    Although bipedal, Ardi lacked the heel and other features required for long distance walking while bearing full weight - or carrying much of anything. Her brain was a little smaller than a comparable modern chimp's.

    Darwinian evolution of major structures (skeletal arrangement, say) requires marginal reproductive advantage to the steps of the transitional changes.
     
  20. FTLinmedium Registered Senior Member

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    Ooh, a few mistakes there, Fraggle Rocker:

    • Protection. A sphere is more resilient to blows from arbitrary directions than any other shape.
    • Efficiency. The physical neural paths should be as short as possible to maximize the speed of cognitive processes- which is mostly irrelevant when the skull is only slightly oblong because most areas of the brain are themselves largely isolated for local processing with only a little communication in-between and themselves possess odd shapes even in spherically skulled animals.
    • Cooling. The brain uses a significant portion of our energy and therefore generates a significant portion of our waste heat and a long skull radiates more heat, thus making it better at cooling. But this isn't a benefit because for the bulk of human history, retaining heat has been more important than cooling
     

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