Interweaving Evolution & Hybrid Vigor

Ahhh, I see where you were going with this. I certainly agree that evolution is not a straight-line linear progression, but favors a mosaic, as you say. I don't think I have seen the Copelemurs on the charts before. Interesting. Is there a cladogram for this group? Whether the trend appears gradual or punctuated depends on where the branch is connected to the main trunk. What I don't like is that the author connected the red line to the mean of the different groups, but just made a basically straight line for the gradualism chart. I think you make a good case for that. I think it is just a difficult and complex thing to nail down. We are just getting to the level where we can handle the kind of data needed to understand population, community and genetic networks. It's an exciting time to be a scientist! Naw, Medical marijuana maybe? HBDEdited by herebedragons, : No reason given.

Sadly I don't have one, however I do have a link to the Gingrich paper where the grapic (afaik) originates (which is sort of like a cladogram bedded in the spatial\temporal matrix): SYSTEMATICS, PHYLOGENY, AND EVOLUTION OF EARLY EOCENE ADAPIDAE (MAMMALIA, PRIMATES) IN NORTH AMERICA by Philip D. Gingerich and Elwyn L. Simons.see Page 32 for the graphic. There is also a long discussion of Copelemur and Pelycodus and their distinctions and relationships. Note that names used there differ from those used elsewhere (a not uncommon thing) and he gives reasons for these changes. The abstract is a good starting point:

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Abstract.-- Several large new collections of early Eocene Adapidae have been made in recent years from stratified sediments in the Big Horn Basin of Wyoming. These collections permit a much more detailed reconstruction of the evolutionary history of the genus Pelycodus than was previously possible. Restudy of the described collections of early Eocene Adapidae indicates the following taxonomic modifications: "Pelycodus" tutus Cope is made the type of a new genus Copelemur, which includes also C. praetutus, C. feretutus (nov.), and C. consortutus (nov.). Restudy of New Mexico fossils from the Largo and Alrnagre facies indicates that Pelycodus jarrovii and Pelycodus frugivoms are senior synonyms having priority over P. venticolis and P. nunienus, respectively, from the Lost Cabin beds of Wyoming. Four additional North American species of Pelycodus are recognized: P. ralstoni, P. mckennai (nov.), P. trigonodus, and P. abditus (nov.).

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A single lineage of Pelycodus is known from Sand Coulee, Graybull, and Lysite beds, but in Lost Cabin beds two lineages are known that were both almost certainly derived from the Lysite species Pelycodus abditus. Samples of species from successively higher stratigraphic horizons are progressively larger, until the second lineage of Pelycodus appears, after which one lineage begins to decrease in size while the other continues to increase. This is interpreted as a probable result of character divergence in body size to minimize competition between the two sympatric species. The mesostyle and hypocone become progressively larger through time in Pelycodus. The evolution of Pelycodus appears to be continuous and gradual from the earliest to the latest species.

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Pelycodus jarrovii is perfectly intermediate between earlier Pelycodus and later Notharctus, showing that the generic transition from one to the other was also both continuous and gradual. The fossil record is now sufficiently complete that the boundary between Pelycodus and Notharctus is necessarily arbitrary. One morphological characteristic, acquisition of symphyseal fusion, appears to coincide approximately with the Wasatchian-Bridgerian (early Eocene-middle Eocene) boundary. The evolution of early Eocene Copelemur appears to have paralleled that of Pelycodus, but detailed evidence is not yet available. The origin of middle Eocene Smilodectes is not yet clear, but an origin from Pelycodus frugivoms or Pelycodus jarrovii appears likely.

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Note the discussion of the speciation event and divergence near the top of the graphic with one branch getting smaller while the other continues to get larger: "... Samples of species from successively higher stratigraphic horizons are progressively larger, until the second lineage of Pelycodus appears, after which one lineage begins to decrease in size while the other continues to increase. This is interpreted as a probable result of character divergence in body size to minimize competition between the two sympatric species. ... " -- this would be an example of the reinforcement selection you mentioned earlier.I also like where he says " ... The fossil record is now sufficiently complete that the boundary between Pelycodus and Notharctus is necessarily arbitrary. ... " as this is typical of what happens as more and more fossils are found. One can hope that a more complete picture\record of Copelemur and it's relationship to Pelycodus will also emerge with more fossils are found. This was written in 1977 after all.Scary thing, when doing a google on this one of the results was an EvC posting ... by me ... Painkillers for recent nasal basal cell carcinoma (non-malignant) surgery & skin graft (a friend says it looks like a nose piercing that went bad ).EnjoyEdited by RAZD, : added

Evidence does not match expectation, it is the expectation (random mating) that is wrong. Now if we consider {a} to have been a previously rare allele that is selected at a same normal frequency in the formation of the sub-population as it moved into a new habitat, ... and that it was beneficial there and increased 120% in a generation, ... but now the sub-population rejoins the parent population where {A} is still ~90%, and where {a} already existed as a selection neutral or mildly deleterious allele (hence the original rareness), ... this would not result in a significant rise of q in this recombined parent population, but one verging on stochastic variation within the large population from generation to generation. There would be virtually no difference in fitness of {aa} in this large population, no reason for selection to favor it this time around, no reason for it to expand in that population.So I don't see an existing, if rare, allele causing a significant change to the combined species population. There was a cause (selection, etc) that it was rare in the original population, and that cause would continue to operate. At best it could result in population subdivision if that new habitat continues to be used. This would act to keep {a} in the overall population, but still not become a major player in the overall population and not lead to takeover from the original population with a derived population.And even if taken to an extreme where the {a} allele achieves 90% frequency in the sub-population, when the populations rejoined the {aa} genotype could not be genetically incompatible with the parent population as it already exists there in small numbers (all things being equal and {aa} not being detrimental there).Certainly it cannot provide greater fitness in the original habitat as it already existed there. So I do not see this type of placid isolation and return changing things for the species population.But if we consider {a} to be derived by mutation in the small population then the picture changes. It enjoys faster selection in the small population and then when they rejoin the parent population (where q = 0) they would have an effect on the population. If the {aa} form is beneficial in the original habitat then it would continue to rise in frequency. It may or may not take over the whole population, depending on fitness.EnjoyEdited by RAZD, : clrty

See Extent of Mutational Capability, message 109 and Message 110, Message 113 and Message 123 -- recent evidence of four more recent Homo species interweaving behavior.Also see A frog with a doubled genome -- interweaving evolution in frogs.So I would not be surprised to see more evidence of periods following population isolation, with subsequent isolated evolution of different traits, being occasionally interrupted by brief rejoining, with hybridizing and mixing of those traits, before reproductive incompatibility arises.The isolation can be due to geography\ecology and it can be due to different mating preferences in sub-populations.Certainly this means that speciation is not as cut and dried as was previously thought.If we consider that reproductive incompatibility is not a necessary aspect of the evolution of isolated sub-populations, that there is no selection pressure for that to occur, we end up with a lower bar for speciation -- mating preferences.The more the subspecies evolve different traits, the more members of each subspecies will prefer mates from their own population over the other, and then it becomes less likely that interbreeding occurs, but not ruled out.When the difference between such species reaches the same degree of differences that are used for phyletic (linear) speciation we are then able to call them different species. From Introduction to Evolution:

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If we look at the continued effects of evolution over many generations, the accumulation of changes from generation to generation may become sufficient for individuals to develop combinations of traits that are observably different from the ancestral parent population.

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(2) The process of lineal change within species is sometimes called phyletic speciation, or anagenesis.

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This is also sometimes called arbitrary speciation in that the place to draw the line between linearly evolved genealogical populations is subjective, and because the definition of species in general is tentative and sometimes arbitrary.

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This adds an amount of uncertainty and arbitrariness to divergent speciation (ibid):

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... there is a second process that results in multiple species and increases the diversity of life.

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(3) The process of divergent speciation, or cladogenesis, involves the division of a parent population into two or more reproductively isolated daughter populations, which then are free to (micro) evolve independently of each other.

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The reduction or loss of interbreeding (gene flow, sharing of mutations) between the sub-populations results in different evolutionary responses within the separated sub-populations, each then responds independently to their different ecological challenges and opportunities, and this leads to divergence of hereditary traits between the subpopulations and the frequency of their distributions within the sub-populations.

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Over generations phyletic change occurs in these populations, the responses to different ecologies accumulate into differences between the hereditary traits available within each of the daughter populations, and when these differences have reached a critical level, such that interbreeding no longer occurs, then the formation of new species is deemed to have occurred. ...

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Perhaps instead we should say:" ... such that interbreeding becomes rare, then the formation of new species can be deemed to have occurred. ... "Enjoy