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Thread: My classification of genus Homo

  1. #1
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    My classification of genus Homo

    I have been struggling with the scientific classification of genus Homo for decades, especially what should be reduced to subspecies instead of full species. I have recognized only three species for quite some time, but I wonder if there are more major subspecies that should be added to those that I recognize below. Suggestions would be welcome.
    Below is my present classification with symbols to the left showing their cladistic (or sometimes paraphyletic) relationships. The alphanumeric coding is cladistic (showing the cladistic order in which they split off). the underlined _a_ indicates that it is an exgroup from the taxon just above it, making that taxon paraphyletic (indicated by the % symbol following it).

    1 Homo habilis%

    1 H. h. rudolfensis

    2A H. h. habilis

    2B H. h. floresiensis ("hobbit")

    3 {{H. erectus + H. sapiens}} (exgroup marker)



    _a_ Homo erectus%

    1 H. e. georgicus

    2 H. e. ergaster

    3 H. e. erectus%

    _a_ {{Homo sapiens}} (exgroup marker)



    _a_ Homo sapiens

    1A H. s. antecessor

    1B H. s. cepranensis

    2 H. s. heidelbergensis%

    _a_ H. s. neanderthalensis

    3 H. s. rhodesiensis

    4 H. s. idaltu

    5 H. s. sapiens

    ---------------------------------------------------------------------------------------------------------------------------------------------------

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     VytautusofAukstaitija (06-16-2019)

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    One debatable taxon is Homo naledi. I obviously do not believe that it merits full species status. However, should it be classified as a full subspecies of Homo erectus? Or is it just a synonym of Homo erectus ergaster.

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    Grouping of species and sub-species should serve a useful purpose. I do not know what purpose your 3 species system serves, but it is interesting to see such a small grouping proposed. I think it is more useful to subdivide into more species, so lets start with some questions.

    a) It there a good reason to include heidelbergensis under Homo sapiens? I don’t see this grouping as useful. heidelbergensis was probably ancestral to both neanderthalensis and sapiens.
    b) Does floresiensis belong under habilis with any certainty? From what I read I think it is more likely a variation of georgicus.

    Why not start by defining what classification system you are using? In the ornithological literature they are used to working with species that hybridize and they have developed working techniques to distinguish between species and sub species. Using these techniques, I expect neanderthalensis and sapiens would be different species because there is good reason to believe the first generation hybrids were at a genetic disadvantage.

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     xenus (06-17-2019)

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    Hi Garvan, Thanks for responding and asking great questions.
    (1) A 2017 paper by Argue, et al., concluded that floresiensis is related to habilis (not erectus or sapiens). They say "A close phylogenetic relationship between H. floresiensis and H. erectus or H. sapiens can be rejected.": https://www.ncbi.nlm.nih.gov/pubmed/28438318
    (2) Even if first generation hybrids (of neanderthalensis and sapiens) were at much of a genetic disadvantage (which is debatable), there are examples in various vertebrate species called "circle of subspecies" (or "ring species"), where there is a chain of subspecies and the populations at the ends of the chain no longer interbreed at all when they meet (and yet the subspecies within the chain still interbreed). And the example of neanderthalensis and sapiens certainly hadn't reached the extreme of no interbreeding at all that is seen in circles of subspecies. I think fewer and fewer biologists are regarding neanderthalensis and sapiens as separate species.
    (3) As for heidelbergensis, my classification shows it as directly giving rise to neanderthalensis. However, Homo sapiens sapiens almost certainly originated in Africa, so its arose from African subspecies such as rhodesiensis and idaltu (not from heidelbergensis). I therefore regard evolutionary trees showing heidelbergensis giving rise to sapiens as overly simplistic and not helpful at all.
    Last edited by kinman; 06-16-2019 at 02:37 PM.

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     VytautusofAukstaitija (06-16-2019)

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    I am thinking that dentition can serve as a delineator for species. Though not a scholar in this area I was introduced to mammalian taxonomy as an undergrad 40 some years ago. There were “lumpers” and “splitters” who differed in their approaches to delineation of species. Genetic continuity and morphology tend to go hand in hand. If we look at other mammals, in general, to belong to the same species there has to be significant interbreeding or no fertility-related barriers to interbreeding to be lumped into one species. To be separated into 2 or more species there has to be genetic isolation (rare productive interbreeding, like dogs and coyotes or coyotes and wolves) and readily discernible morphological differences like dentition or skull morphology that does not overlap. There are often cases of overlap. The remnant of red wolves in SE US for example seems to have wolf and coyote genes. Such overlap is common when there are bottlenecks and species outbreed because they cannot find mates of their own species.

    Another interesting wildlife species decision is the caribou of North America and reindeer of north Eurasia. Scientists differ on whether they are one species or variants of one. I’m sure most here would consider them one because their skeletons overlap morphologically.

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    As for "significant interbreeding or no fertility-related barriers to interbreeding", that is often very difficult to test when the populations in question are isolated at the present time (islands in the oceans, isolated on different mountains, etc.). A splitter will detect some small difference and declare them separate species, whereas a lumper will see the minor differences as simple variation due to factors such as founder effects.
    It is obviously far more difficult when dealing with fossil taxa which are usually very fragmentary and often few in number. Therefore, it is not surprising that there seem to be a lot more splitters among anthropologists. And they make a bigger splash in the literature describing new species rather than subspecies.
    I tend to be a lumper, but there are lumpers that I feel carry things too far. There are those who would lump Homo habilis and Homo erectus into a single species, but excessive lumpers will just give excessive splitters an excuse to defend their splitting.
    -------------Ken
    P.S. I am not against recognizing more than three species in genus Homo, but there would have to be strong reasons to recognize a fourth or fifth species. And I don't even consider expanding Homo to include Australopithecines (much less classifying the chimpanzee as Homo troglodytes as I have seen suggested).

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    I like your approach; it’s different and provokes thought. What do you think of dentition as a criteria? I’m pretty sure that for extant mammals, significant differences in dentition would be justification for splitting. The reason I’m focusing on dentition is that teeth are often recovered.

    I really don’t know anything about whether modern humans have the same number and general form of teeth as neanderthalis or heidelbergensis.

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    1) Thanks for the link to the 2017 paper on floresiensis. I saw the abstract before, but I do not have access to the full paper so I was probably more influenced by older ideas that georgicus was a better match in terms of physical size, variable archaic features and location (outside Africa). I can’t find any recent sources to support this opinion, so I now am inclined to agree with your classification H. h. floresiensis.
    2) Regarding ring species, there is no genetic disadvantage to the hybrids of the different sub-species. If there were and it could be demonstrated, then that would be evidence that it was not a ring species. The evidence of genetic disadvantage to neanderthal and sapiens hybrids is from the genome of modern sapiens which has deserts from which all neanderthal genes appear to have been purged by selection.
    3) Chris Stringer believes that rhodesiensis has been misdated, and it represents a population with archaic traits that survived in Africa until relatively recently. If he is correct, then what should we call the African Homo contemporary with heidelbergensis (600,000 to 250,000 ybp)? Idaltu is too young (160,000 ybp). I am using heidelbergensis but take your point that it may be over simplistic.

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    Hi Garvan,
    Regarding "the evidence of genetic disadvantage to neanderthal and sapiens hybrids from the genome of modern sapiens which has deserts from which all neanderthal genes appear to have been purged by selection." I do not find such evidence as definitely demonstrating major genetic disadvantage.
    Frankly I am amazed that modern populations still have 2-4% Neanderthal DNA after all this time. Given those long periods of time, the loss of such genes could be due to chance (rather than indicating that they were deleterious). I think more studies are needed on that subject.
    Furthermore, one article states that " alleles – or gene variants – inherited from Neanderthals had only decreased by 56 percent, tens of thousands of years after the initial interbreeding occurred. This suggests that they were eliminated very slowly, indicating that they probably weren’t as detrimental to the reproductive success of hybrids as previous theories claimed." Source: "Neanderthal Genes May Not Actually Be That Harmful To Humans": https://www.iflscience.com/health-an...armful-humans/
    Even if there were some Neanderthal genes eliminated because they were deleterious, a lot more attention needs to paid to the genes that have persisted because they were advantageous. Neanderthal-modern human hybrids may have actually been healthier than their parents, not disadvantaged at all. This needs to be more thoroughly researched and debated.
    ------------------Ken

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    Hi RP48,
    Evidence provided by dentition in Homo seems to me less important than it is many other mammals. More important in genus Homo seems to be the maxillary and mandibular bones which held the teeth (as well as the cranium above). I would only pay attention to dentition changes that can be correlated with changes in the rest of the skull. Otherwise, dental changes could be misleading.

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