homo species definition

Discussion in 'Human Science' started by mathman, Mar 19, 2018.

  1. mathman Valued Senior Member

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    There is strong evidence that modern humans interbred with Neanderthals and Denisovians. In that case shouldn't all three be considered one specie, with homo sapiens a subspecie?
     
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  3. Gawdzilla Sama Valued Senior Member

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  5. iceaura Valued Senior Member

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    Breeding isolation is only one of the criteria for establishing separation into species. There are many examples of groups of related species that can successfully hybridize - most of the different species of canids, felids, and quercids (oak trees), in North America, for example.
     
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  7. Beer w/Straw Transcendental Ignorance! Valued Senior Member

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    Just for the know (because I didn't know when a friend told me):

    "The liger is a hybrid cross between a male lion and a female tiger. The liger has parents in the same genus but of different species. The liger is distinct from the similar hybrid tigon, and is the largest of all known extant felines." https://en.wikipedia.org/wiki/Liger
     
  8. sculptor Valued Senior Member

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    A species is often defined as the largest group of organisms in which two individuals can produce fertile offspring.
    Being that some of us carry neanderthal and/or denisovian dna, we would then all be of the same species.
     
  9. iceaura Valued Senior Member

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    That is one often useful demarcation, which a taxonomist may choose to employ (with others, of course) in characterizing a taxon - that one is useful for characterizing a genus, or sometimes a species.

    As a definition it is an error - many species can produce fertile hybrids with other species. It's possible that most can, or could before extinctions of the past.

    Apparently all or most of Darwin's Galapagos finch species can produce fertile hybrids, for example. That may be how several of them evolved in the first place.
     
  10. mathman Valued Senior Member

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    These are sterile hybrids - so lion and tiger are different species. Similarity with horse and donkey.
     
  11. billvon Valued Senior Member

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    Doesn't really follow. Having some DNA from a different lineage in us is no guarantee that homo sapiens and any other subspecies are still cross-fertile.
     
  12. sculptor Valued Senior Member

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    Would it not then follow that when our ancestors successfully bred with neanderthals and denisovians, creating fertile offspring, that they were not homo-sapiens-sapiens, nor homo-sapiens?
    If so, what then were they?
     
  13. billvon Valued Senior Member

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    Might be a different subspecies, might be the same species.

    Keep in mind that pretty much every time a new species splits away from an existing lineage, there is a period of time where crossbreeding is possible. As time goes on, crossbreeding works less and less reliably; often, offspring are sterile, crippled or nonviable. At some point it is nearly impossible, and eventually it can't happen at all. It's hard to pick a time where you can say with certainty "ok NOW they are really a separate species."
     
  14. sculptor Valued Senior Member

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    Perhaps?
    Especially when we cannot be certain:
    Perhaps it is still best to add the phrase "most likely" or the word "possibly".
    (now, they are most likely a separate species) or (now we/they are possibly a separate species)
    Or--------we are most likely a different sub-species
    ?
     
  15. iceaura Valued Senior Member

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    No. It is possible, but does not necessarily follow.
    If they can't hybridize with fertility, they are (usually*) separate species. The converse is not true. It is a sufficient but not necessary criterion.

    There are many separate species that can hybridize and produce fertile offspring. Dogs and wolves and coyotes, some willows and oaks, some gulls and some ducks, the Galapagos finches, etc., are convenient examples of a very long list. There are even categories called "ring species" https://en.wikipedia.org/wiki/Ring_species.

    There are ongoing projects to breed disease resistant American chestnuts and American elms via crossbreeding with different species. There are ongoing projects to recreate recently extinct species by backcrossing extant hybrids - European wild cattle, some kinds of wild birds. These all involve fertile hybrids of established, formal, named, separate, species.

    We are at the mercy of professional taxonomists, in this. It is not a layman's philosophical issue.

    (*There's some kind of taxonomic battle or discussion in the literature involving Wolbachia infection of mosquitos and other insects - the infection creates subpopulations within a species that suddenly cannot interbreed. https://en.wikipedia.org/wiki/Wolbachia The question is whether and under what conditions that indicates the creation of a separate species. )
     
    Last edited: Mar 21, 2018
  16. mathman Valued Senior Member

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    It looks to me that the concept of "species" is not well defined. At one time I thought the definition was, if two individuals could produce fertile offspring, they were of the same species, but that doesn't seem to be the case.
     
  17. RainbowSingularity Valued Senior Member

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    maybe the new sub species had a more developed frontal lobe with social traites that allowed better learning in children to learn language and social custom before the others resulting in them be ableto start learning tactical thinking along with hunting at a much younger age.
    this would place them in a much superior position and ongoing cultural development would define the other species as far inferior resulting in genocide of the other species to protect the newer group ?
    just a casual thought.
     

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