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Have we ever observe significant macro evolutionary changes

  1. Dec 9, 2009 #1
    I am looking for examples of significant macro evolutionary changes that have actually been observed. I am aware of instances where speciation has been observed, but in those examples, the changes do not seem that significant or dramatic. I guess the kind of changes I'm talking about are those in which we would see one species (I'll call it species A) evolving into another species, with the new species in turn going through their own speciation, until ultimately a species emerges that could be classified in a new genus, distinct from the genus of species A. This is how evolution is supposed to work in theory, but have we ever actually observed that many changes.
     
  2. jcsd
  3. Dec 10, 2009 #2
    If what you are looking for is evolution happening within a controlled experiment, the closest you'll get is probably controlled evolution of e.coli strains (http://myxo.css.msu.edu/ecoli/). I expect these experiments to show fairly dramatic changes, but probably not qualifying for new genus. Other than that artifical evolution of domesticated animals and some plants has been going on for centuries and could be regarded as controlled experiments, but I don't know if you'll find anything there that meets the criteria of new genus (which is a subjective classification anyway).

    Study of fossil records and genetic variations between species draws a pretty nice picture of the evolutionary record, but I understand that this is not what you are looking for.
     
  4. Dec 10, 2009 #3
    It is probably the case that we haven't been experimenting/documenting the natural world long enough (says the electrical engineer). I've read a few articles which describe observed speciation of an organism, but not a new genus.
     
  5. Dec 11, 2009 #4
    So the fossil record and genetic changes are the only real evidence that significant evolution beyond the species level has occurred. It just seems like we should have had enough time to observe major changes in the real world.
     
  6. Dec 11, 2009 #5
    It turns out it is not. And I am not really surprised. If you consider the large amount of functions that has to be gained and lost for two species to be classified into different genus and the short time that we have been developing evolutionary theory (150 yrs). For the kinds of species we can easily observe 150 yrs is not many generations. The last 20-30 years it has become feasible to study the evolution of microorganisms in a controlled way and just to get a perspective on the timescales that might be needed: one strain of e.coli used more than 30.000 generations to evolve a novel function that would increase its fitness in its environment (the capacity to utilize citrate). Now, I think we would need quite a lot of novel functions before you would call this "evolution beyond the species level"

    That said. Why would you expect evolution to stop at some point? If you consider an isolated population of some species whose environment is gradually changing to favor the species changing a lot from its remote relatives other places in the world. Why would you expect them to be unable to change beyond some point by which we define their genus?
     
  7. Dec 13, 2009 #6
    It sounds like there is still widespread disagreement on what changes constitute classifying a creature as belonging to a new species or genus. Also, I am trying to understand the relationship between genetic changes and actual physiological changes within a creature. If speciation occurs, does that mean new genetic information has been added to the DNA of a creature's genome, or does that just mean that certain parts of the DNA that were once inactive have become activated?
     
  8. Dec 13, 2009 #7
    When has speciation been documented? You have the papers handy? I'd like to read those.

    I dont think that 'macroevolution' exists in scientific world though, it's just more of a term created by those who do not support evolution in order to seperate evolution which we have and we continue to see from the grande-level speciation which we haven't (to my knowledge). This is of course kind of rediculous considering we have not been exactly studying species and their genes etc. for all that long so how is anyone going to expect that it will have occured
     
  9. Dec 13, 2009 #8
    If you do a search for speciation, you can find examples. However, the problem is that there is such widespread disagreement on the meaning of species that those examples don't really help. Evolutionary scientists do not concern themselves with such little changes, but rather look for apparently major changes in the fossil record. The distinction between macro and micro evolution was probably promoted mostly by creationists since they held that microevolution has been observed while macro evolution has not. Evolutionary scientists seldom utilize those terminologies, except I suppose when debating creationists. I wouldn't get bogged down in splitting hairs over such distinctions, but am more concerned with finding evidence that major changes have actually occurred in the past.
     
  10. Dec 14, 2009 #9
    I think one of the ways new functionality can occur through evolution is by parts of the genome being duplicated, so that certain proteins are coded for redundantly. One of these codes are then free to change so much that it no longer performs its original function. This can then again from the basis for new functions, but it might in the mean time become "inactive", as you say (basically, a mutation killing the signals for transcribing a genetic region need not have severe effects on an organism which have duplicate codes for the protein encoded by that region).

    So in my opinion, one way the additions and loss of organismal functions involved in speciation relate to both adding of information (duplication of at least parts of genome) and later activation of "inactive" (untranscribed) parts of one of the duplicates after this has been undergoing mutations and recombinations.
     
  11. Dec 14, 2009 #10

    sylas

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    Depends what you mean by "major". Evolution works by the accumulation of lots of change. "Macroevolution" is not a different kind of change to contrast with "microevolution". Even large changes in a single generation are still "micro" change, by the definitions of these terms I am used to. I tend to use "microevolution" to refer to the changes from generation to generation that occur within a species; and "macroevolution" to refer the accumulated differences between lineages that have diverged.

    There have been cases of substantial change over short periods of time (rapid evolution) but the time scales available are not generally enough to give what most people would think of as macroevolution, or significant morphological divergence of separated lineages.

    Biology is messy; hard and fast rules are hard to come by. There are some cases (especially in plants) where you can get substantial change in a single generation that can be identified as the origin of a new species. Maize is a likely example. With animals, sexual reproduction makes this much less likely.

    Cheers -- sylas
     
  12. Dec 14, 2009 #11
    Hmm I have to disagree with you here sylas. 'Macroevolution' does not have to be an accumulation of microevolutionary events. Nor does it have to take a longer amount of time, I read a study done on this. Large evolutionary events can occur very rapidly and without any small evolution preceding it. Look at how quickly the speciation in humans had occured.
     
  13. Dec 14, 2009 #12

    sylas

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    How quickly do you think speciation occurred for humans?

    I did note that there are some exceptions to the rule (Maize being a possible example) but that animals don't tend to show such exceptions. Humans, being animals, are very much a case where macroevolution (divergence between species) is by accumulations of microevolution (change within a species).

    Cheers -- sylas
     
  14. Dec 14, 2009 #13
    I have no idea what the terms 'microevolution' and 'macroevolution' mean to you. There have been scientific studies done which show conclusively that macroevolution, as the term I understand is used, occurs much in the same way that 'microevolution' occurs and does not need to be a compilation of 'microevolutinary events'.
     
  15. Dec 14, 2009 #14
    It has very recently been published an interesting computational study attempting to quantifiably address how common burst-speciation happens relative to more gradual accumulation of minor changes:

    Phylogenies reveal new interpretation of speciation and the Red Queen
    Chris Venditti, Andrew Meade & Mark Pagel

    http://www.nature.com/news/2009/091209/full/news.2009.1134.html?s=news_rss

    doi:10.1038/nature08630

    unfortunately this is behind a paywall still.
     
  16. Dec 14, 2009 #15

    sylas

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    I defined the terms above. I refer to microevolution as change within a species or gene pool, and macroevolution as change above the species level, or between distinct gene pools.

    You will need to cite these studies for me; and indicate what definitions of the terms you are applying. I think you may be mistaken.

    The definitions I am using are pretty standard in biology; though they can be expressed in different terms. A good accessible reference is the talkorigins FAQ Macroevolution: Its Definition, Philosophy and History. My link is to the initial section of the FAQ "What is macroevolution"; but the whole page is very informative. It considers alternative definitions and ambiguities that can arise -- for example, it can depend on what definition of species is being used.

    The author, John Wilkins, is a philospher of biology, with particular expertise in species concepts. The FAQ is extensively referenced to the relevant literature.

    Also relevant is the comprehensive FAQ at talkorigins: 29+ Evidences for Macroevolution; which sets out the definition in the first paragraph.

    For macroevolution to be NOT via a complication of microevolutionary changes, you would have to have a change that is not broken into smaller changes; a single massive jump in a generation. This is highly atypical; if it occurs at all. It certainly does not occur in humans. It may have occurred with maize, as I have suggested previously, although even there I consider that macroevolutionary change to maize from its ancestral wild species (teosinte) is properly understood as an accumulation of microevolutionary change; whether or not some of the individual steps were particularly significant. Reference:

    Cheers -- sylas

    Postscript added in edit:
    Thanks for the reference. I have looked it up. The link you give is to a news report about the publication; the advance online publication itself is http://www.nature.com/nature/journal/vaop/ncurrent/full/nature08630.html (still a paywall, but I have access).

    This paper involves inferences about a variable rate of evolution based on computational analysis of phyogenies. What is a bit irritating about this paper occurs in the publicly accessible abstract:
    The Red Queen describes a view of nature in which species continually evolve but do not become better adapted. It is one of the more distinctive metaphors of evolutionary biology, but no test of its claim that speciation occurs at a constant rate has ever been made against competing models that can predict virtually identical outcomes, nor has any mechanism been proposed that could cause the constant-rate phenomenon.

    The reference to the "Red Queen Hypothesis" goes to a paper in 1973, and the note that there's no mechanism to enforce constant rate evolution goes to Stenseth, N. C. & Maynard Smith (1984); but the references omit all the main references for whole punctuated equilibrium debates prior of the 1970s and early 1980s. Evolutionary theory has never required a general constant rate hypothesis; and bursts of change still involve the accumulation of microevolutionary change, just like gradual changes or periods of comparative morphological stasis. It's about the rate of change and the divergence of gene pools.

    The methods of the paper cannot actually identify the causes involved, but the paper singles out the idea of "reproductive isolation".
    Factors apart from biotic interactions that can cause speciation include polyploidy, altered sex determination mechanisms, chromosomal rearrangements, accumulation of genetic incompatibilities, sensory drive, hybridization and the many physical factors included in the metaphor of mountain range uplift.

    Reproductive isolation is basically what allows lineages to diverge. As long as you have an interbreeding gene pool, changes tend to mix through the population or be eliminated. For speciation to occur it is probably necessary to prevent mixing, so that changes accumulating in two pools can diverge. Change is still by the accumulation of small changes, but it can occur at different rates and the capacity for divergence of distinct lineages arises when something occurs to prevent mixing between two gene pools.

    Cheers -- sylas
     
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