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Thread: How to define "species" of an organism if...

  1. #1 How to define "species" of an organism if... 
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    How do biologists determine the species of an organism if it reproduces asexually? How would we know if this organism underwent speciation?


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    WYSIWYG Moderator marnixR's Avatar
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    that's where the species concept of interbreeding populations breaks down, just like it does if you add time to the equation for what we consider to be "normal" species
    in that case biologists usually fall back on the morphological definition of species, based on external characteristics such as how it looks like, what its behaviour is and what its preferred niche is


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    Forum Cosmic Wizard spuriousmonkey's Avatar
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    The ability to breed is just one aspect of one species definition.

    Species can be defined in different manners, and usually it is done so with a specific scientific purpose in mind.

    In fact, the ability to interbreed is a definition which is mostly pretty useless in most aspects of science. Do you think scientists go out into the field, take two random specimens, and check whether they belong to the same species by checking if these two specimens can interbreed?

    No.

    For fossils there is absolutely no evidence at all of interbreeding, so this definition cannot be used at all here either.

    The interbreeding definition comes more from the theoretical structure of the theory of evolution. It's not a practical one, other than in population biology they will speak about breeding populations; groups of individuals which interbreed and are connected by the process of interbreeding. They don't actually check whether they all interbreed. Are two populations of deer that are separated by a big river then two species because they aren't interbreeding with each other?

    They could be and could not be. It all depends on other factors.

    reproducing asexually poses the same problems as sexually reproducing organisms. It is absolutely impossible to say where one species ends, and the other begins, because it is a continuous spectrum of intermediates.

    Defining species is only possible if you stop in time and take an inventory. And there will always be hard cases when you do that due to the nature of evolution.

    Maybe it is also a source of confusion for creationists and IDers since they don't tend to see the whole pictures. They also see ready-made organisms separated by oceans of difference.

    However, just look back, forward, or more deeply and you will see only distributions of character shifting in time and space.

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    Forum Cosmic Wizard paralith's Avatar
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    I'd just like to add that the biological species concept, which is based on interbreeding, does not simply state that two species cannot interbreed, but that they do not. In other words, they may be perfectly capable of physically producing offspring, but perhaps due to other factors like geographic separation, different mating behaviors, different breeding seasons, etc, do not interbreed naturally. The key here is a disruption of gene flow between the two groups; for whatever reason, they do not share genes so that traits which arise in one group do not necessarily spread to the other as well. No, you can't tell if two organisms interbreed in nature if you just pluck them from their populations and look at them. But if there is a large number of traits that differ between them, it's less likely that they're part of populations that share genes with each other. The biological species concept is more theoretical but it does give rise to predictions about differences between two organisms that we would expect if they're from different species. Even aesexual reproducers like bacteria can still pick up genes from each other from time to time.
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    WYSIWYG Moderator marnixR's Avatar
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    the following article on Bdelloid rotifers may be of interest
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