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How is speciation possible within known confines?

  1. Feb 27, 2017 #1
    Please someone help me understand the concept of the actual occurrence of speciation. Cataclysmic Evolution may account for some species but not many, it could only practically apply to asexual species and would undermine genetic diversity. Actually I can save a lot of explanation by clarifying. So, to clarify, for this question, I am using the term "species" to refer to one group that has mating incapability with another group and I am generally referring to complex animals. Back to it... Gene duplication and tandem multiplication might alter one family group over time, but doing so in a similar way to many families of the same species so that speciation occurs at the same time to allow for reproduction, the odds are astronomical. And if reproduction of a new species always occurred within the same family, or even one or two other families, every new species would suffer the ill effects of close inbreeding. No chance to break the cycle of inbreeding depression by outbreeding. Most complex organisms, (I'm talking mammals here), need approximately 50 (give or take) unrelated or distantly related members of the species to not develop species-wide weaknesses. Genetic Variation is even even less likely to cause viable speciation, more of a chance of a new Big Bang than for every new sexual species with a simultaneous breeding pair. Especially considering the fossil evidence of Punctuated Equilibrium, where these changes have to occur within a few hundred generations, the odds of any speciation is incalculable. This holds true even taking into account hybridization as a segue. Neutral theory and good old synthetic theory fall into this "odds are unmeasurable" category as well. (That is, of course, unless molecular evolution is deterministic, as some researchers have said, but I refuse to accept that it's all being directed by some unseen power.) All of these theories do a great job explaining adaptation and natural selection of traits within a species, but they all seem to fall just short of allowing for actual generation of a new species. I've looked into the newer research that models species change in way less time than previously thought, but it doesn't seem to take in to account the nessesity of the number of breeders necessary to avoid inbreeding depression.
    So my actual question is: What am I missing?
    (And, please, none of this infinite universe/multiverse/we just are the lucky planet stuff, or the "it is because it has to be" stuff. I'm looking for real research. And I'm sorry for the long question, I figured it would save a lot of unnecessary discussion in the long run.)
  2. jcsd
  3. Feb 27, 2017 #2


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    There's no need for simultaneous occurrence of the same set of mutations in many individuals. All that is needed in one individual, whose fitness-increasing mutation is spread among the population by their offspring. With large enough population, sufficient genetic diversity is maintained while the gene becomes fixed within a few generations. Then another individual's mutation does the same. Or instead of a brand new mutation, there's a previously fitness-neutral gene that synergises well with the new introduction, so the few individuals that carried it now have increased fitness and their gene is also fixed in the population.
    Take a few steps like that, combined with geographical isolation from once genetically-identical populations, and gradually you get a more and more reproductively-isolated and genetically-different species.
  4. Feb 27, 2017 #3


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    Speciation in complex organisms isn't the result of a single event, it is the culmination of many changes over, at minimum, hundreds or thousands of generations. The change in population A from "capable of breeding with population B" to "not able to breed with population B" is also a gradual change. If you were to take an individual from population A just after the two populations were isolated, this individual would most likely be able to breed with another individual from population B. If you leap ahead a few thousand years, another individual from A may still be able to breed with one from B, but with a lesser chance of succeeding or of their offspring being infertile. If we were to repeat this process, we'd most likely find that the chances of successful reproduction between individuals from A and B doesn't suddenly go to zero, but falls off gradually. An intermediate stage would be where an offspring between members of A and B is infertile, just like how donkeys and horses can breed, but their offspring, a mule or hinny, is almost always infertile. Keep jumping forward and eventually you'll find that the chances of breeding become essentially zero as the two populations diverge.

    The accumulation of changes in A and B that eventually prevents them from breeding with each other occurs gradually. A single mutation in individuals in either population does little to affect their fertility with other members of their own population. Because of this, these changes spread to successive generations, each of which have their own mutations, and the net effect is a gradual change that eventually produces two populations that are what we would call "different species".

    So the idea of a single mutation or duplication event in a complex organism leading to speciation is not, to my understanding, how it usually works.
  5. Feb 27, 2017 #4

    jim mcnamara

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    I had an entire graduate level class in what I think you are trying to ask: speciation

    There are a multitude of isolation mechanisms to allow species to remain separate: Physical, behavioral, genetic, biochemical, geographic, temporal.
    Genetic:Chromosomal incompatibility - hybrids die or are infertile.
    Temporal: Mating times can shift so that females can only ovulate at the wrong time for males of a separate species
    Behavioral: mating rituals can differ - bird mating calls for example.
    Geographic: Island species often demonstrate this - i.e., Darwin's finch.
    Physical: coloration changes in the male insect - only the bug with the right "coat" gets to mate.

    Example of geographic - look at at the papers cited for this: https://en.wikipedia.org/wiki/Insular_biogeography
    Learn about the "modes" of speciation allopatric, peripatric, parapatric, and sympatric - https://en.wikipedia.org/wiki/Speciation

    You need to find some kind of primary source, the subject is much too involved for forums. If you REALLY want one please ask, but be aware they take all kinds of "bents", the perches the text requires to take on the side of examining data to interpret it. So you get to wear many hats.
  6. Feb 27, 2017 #5
    Right. That's totally the way I understood it, too. But where the math doesn't add up is with the quick changes that are necessary to match up to the fossil record.
    So, yes, the necessary genes already exist within the species but change has to happen incredibly fast to accomplish speciation within most of the record times, some as little as 200 generations. It'll take approximately 8 or 9 generations to make one physical feature of the same species spread out enough to share that feature with enough of its offspring to allow open reproduction within just a few members to not risk inbreeding depression. Even then, these few will be the vast minority. And we only have the difference of a black Labrador and a chocolate Labrador. There are a lot of other genetic changes that have to work their way into this population before the species can actually change from its previous self. Every time this new modification inbreeds, it increases the species change, but also increases chances of inbreeding depression. Every time the new stock outbreeds, the modification gets diluted. But dilution is necessary to ensure that the negative sides of inbreeding don't stack up on our blossoming species.
    So that's why I was talking about simultaneous mutations. Because, within the tiny group necessary to make such rapid change, it is insanely unlikely that problems from inbreeding won't kill off the new species. But it's equally unlikely that the mutations will form in a larger group fast enough to make changes so fast. And, in such a short number of generations, reproductive isolation will have to occur so fast that, if somehow it doesn't happen simultaneously across one or two generations, the species is more likely to die out from a mixture of sterile babies and shrinking gene pool before it actually isolated.
    So I always understood things to work the way you said. Small changes, over sufficient time, under environmental pressures. But the more I study about the fissile record, it seems that species change doesn't occur this way. That's why I threw in the words Punctuated Equilibrium. The fossil record is rampant with this stuff. Steady species for a hundred thousand of years then all of a sudden a full change within a handful of generations. That's where the math goes wonky. Just not enough time. The dog might become a dingo, but it won't become a fox. At least, not without being a retarded fox with cancer.
    I think that's what got me trying to work this issue. It all added up until I was trying to get rapid speciation seen in the fossil record to cooperate with time needed to avoid inbreeding issues. I've tried finding some kind of study on it, I'm sure it's been addressed somewhere. I've only been able to see studies on each, but not really applied together.
  7. Feb 27, 2017 #6
    So to simplify again (sorry for the web of thoughts), it's not the modes of speciation that I don't get. It's the lack of cooperation between time needed for viable genetic changes and the short times of major species changes that are often seen in the fossil record because of the negative effects of inbreeding.
    I hope I was a little more concise this time. Thanks guys
  8. Feb 27, 2017 #7


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    I'm not sure what you mean. The fossil record is incredibly incomplete and species are often thought to go extinct only for fossils to reappear millions of years later. Even then, we're unlikely to be looking at a single species and more likely to be looking at members of the same genera.

    You're not seeing the full picture, you're only catching a heavily fragmented snapshot. Except for the very recent past, it is very difficult to infer anything on a time scale of less than tens of thousands of years when looking at fossil record. The "sudden" change you're referring to is almost certainly an artifact of incomplete sampling. In other words, you're only seeing a handful of individuals who could have lived in a time where both their own species and a closely related one (perhaps the 'parent' population) were alive. You just don't see any more fossils of the parent population, either because they haven't been found or because there aren't any.
  9. Feb 28, 2017 #8


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    @Cal ben When you say 'the maths does't add up' and 'there's just not enough time', what do you mean, exactly?
    How many generations does it take for a new advantageous gene to become fixed in a stable population of, say, 50*? How long for a set of genes coding for a distinct morphological trait? How does that compare to the scale of rapid changes in the fossil record?

    And what do you mean by 'reproductive isolation must occur so fast'? That initial population of 50 may be already isolated from other populations, e.g. geographically, before it starts to drift genetically.

    *given some example species
  10. Feb 28, 2017 #9
    If 1 member of species developes a gene, it'll take about 8-9 generations to spread to 50 descendants that are distant enough to mate without the downsides of inbreeding. But for this to occur, this has to take effect within a larger, more genetically diverse group or the bad effects will already become a permanent genetic feature. The 50 only allows for breeding, it doesn't allow for species survival. That takes about 150. But that'll only take about 2 more generations to firmly establish. So 10-11 generations. Keep in mind, all these numbers are approximate for mammals and based on work I did in conservation so I am attempting a little bit of cross-discipline research.

    And I apologize about using the phrase 'reproductive isolation'. I was using the word wrong. Post-mating isolation mechanisms is probably a better description. Genetically incompatible is what I was going for. A fundamental physiological change. A single gene changing something simple, like (hypothetically) adding a spot to the back of the head of some of the population can travel that fast, the genetic changes that need to happen to make sweeping alterations won't add up in a few hundred generations.

    Which brings me to my next apology.. to everybody. I went back and read the research paper that kicked off my confusion. I misunderstood something. (Or suffered from acute simultaneous study reading mixed with self induced sleep deprivation, not sure which one) The paper cited two other studies done that built models that demonstrated complex speciation in as little as 200 generations. It claimed fossil record 'will possibly' show this shift one day, not 'has' shown it. Other materials I was reading, simultaneously, put the shortest estimated anagenesis (per record) at about 50000 years. And I think everybody can agree that nobody has been able to take everything into account while building a model. 50k years still seems a bit tight, mathematically speaking, but not enough for me to put a calculator to it.

    Seriously, it's basically impossible to find anything that addresses fossil record without throwing a thousand different models in there. My fault, I suppose, for reading a dozen data-heavy research papers at the same time... after work... exhausted... while sipping bourbon. Bound to get them mixed up. Once again, sorry everybody.

    On a side note, I would like to see some kind of studies done that includes known negative effects of inbreeding with the evolutionary effects of inbreeding. I've read what's out there and the results of evolutionary genetic research doesn't really match what know about conservation genetic research. It feels like evolutionist geneticists and conservation geneticists have a bit of a different viewpoint. I wish there was a way for all the disciplines across the scientific community to end up with the same answers. I guess it all has to do with the small nueances of indavidual research for specific purposes. Not trying to start a new conversation, just something I noticed.
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