4 ms·

What's a Species, Anyway?

8 points by hunglee2 11y ago

jonchang 11y ago
Well, hybridization is certainly not a new theory -- as the article mentions, many plants hybridize quite readily, and the existence of "ring species" just goes to show how fuzzy the biological species concept is. The proper way to think about species is that they are hypotheses to be tested, and evidence can variously favor merging or splitting species. In the case of conservation, there are political reasons for defining species. The laws either have no provision for protecting populations below the species level, or otherwise there's no political will to attempt to do so. Therefore conservation biologists will often try to keep species "distinct" in order to keep what would normally be termed a "population" or "subspecies" under protection. (You might ask why bother protecting populations or subspecies when the larger species is fine -- oftentimes there are suspected local adaptations that would be wiped out by letting that population go extinct or hybridize with other populations.)
Amorymeltzer 11y ago
>The search for the red wolf's origins have led scientists to a new theory about how evolution actually works A close reading of the (beautiful) story shows that while the red wolf presents a nice narrative, there is little truth in this statement. It may have caused much hand-wringing among environmentalists, hunters, and government officials — an important conversation and issue in its own right — but scientists remain quite unsurprised. This is just another in a long-line of cases where "species" is hard to define. The old chestnut of "can't breed" doesn't work in all mammals, much less bacteria where horizontal gene transfer is common. In terms of sequence, it's not as fun to look at, but the best example is probably E. coli. Across all of the E. coli strains only around 40% of the genome is shared in a "core" genome.[1] At first glance that makes no sense and probably says just as much about our characterization of bacterial species as it does our definition of bacterial species. But, really, who cares? The article quotes Darwin: >I look at the term species as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other Which is essentially how scientists use it now. It's very convenient for categorization when it is, but often has no valuable meaning. You can (and should) say the same thing about the definition of life. Are viruses alive? It's an interesting question, but does it change anything? It's okay for some of the edges to be a bit blurry. The fluidity of "species" is, I think, one of the cooler aspects of modern biology. What better way to start teaching kids about evolution and the DNA that connects us all? 1: http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1000344 http://journals.plos.org/plosgenetics/article?id=10.1371/jou...
logfromblammo 11y ago
As a non-biologist, I'll just go ahead and suggest that species are defined by a single genetic exemplar that is an actual common ancestor to all extant members of the species. This individual then recruits additional members by hybridizing with its own ancestor species or sibling species in the same genus. Any given organism's species is determined by the relative genetic distance between it and the species exemplars. Under this regime, if we postulate a new species Homo superior with, for instance, the mutant ability to read and write text messages while also being fully aware of its surroundings, the earliest known bearer of the mutant gene would likely be chosen as the exemplar. If this person died and was not preserved in any way, we might be able to reconstruct a model of their genome via gene sequencing analyses, which would clearly show the mutant gene. It would hybridize with Homo sapiens, the parent species. Children lacking the mutant gene would be indistinguishable from H. sapiens. Children with it would clearly be able to trace lineage to the exemplar. Without barriers to breeding, the new species might just invisibly replace the parent species as a non-branching successor. In this case, we might just let it keep the same species name, and retcon the original mutation into the appearance of a subspecies. The fossil record makes selection of exemplars easier, because in many cases, only one instance even exists. Only one tooth found in Denisov cave. Only one Taung skull found. If there is no gene in Canis rufus that is unique to a single species exemplar, there is no unique species left. Even if it ever was its own species, having a purely theoretical exemplar with only a few known genes, right now it is just a lupus-latrans hybrid. So for me, a species would be defined by the presence of one or more specific genes. Those genes could be determined by sequencing DNA from actual remains, or inferred by analysis of living members of the species. Being able to interbreed fertile offspring seems to me to be more like a genus-level thing, because that seems pretty common in plants.

8 points by hunglee2 11y ago

Well, hybridization is certainly not a new theory -- as the article mentions, many plants hybridize quite readily, and the existence of "ring species" just goes to show how fuzzy the biological species concept is. The proper way to think about species is that they are hypotheses to be tested, and evidence can variously favor merging or splitting species. In the case of conservation, there are political reasons for defining species. The laws either have no provision for protecting populations below the species level, or otherwise there's no political will to attempt to do so. Therefore conservation biologists will often try to keep species "distinct" in order to keep what would normally be termed a "population" or "subspecies" under protection. (You might ask why bother protecting populations or subspecies when the larger species is fine -- oftentimes there are suspected local adaptations that would be wiped out by letting that population go extinct or hybridize with other populations.)

Amorymeltzer 11y ago

>The search for the red wolf's origins have led scientists to a new theory about how evolution actually works A close reading of the (beautiful) story shows that while the red wolf presents a nice narrative, there is little truth in this statement. It may have caused much hand-wringing among environmentalists, hunters, and government officials — an important conversation and issue in its own right — but scientists remain quite unsurprised. This is just another in a long-line of cases where "species" is hard to define. The old chestnut of "can't breed" doesn't work in all mammals, much less bacteria where horizontal gene transfer is common. In terms of sequence, it's not as fun to look at, but the best example is probably E. coli. Across all of the E. coli strains only around 40% of the genome is shared in a "core" genome.[1] At first glance that makes no sense and probably says just as much about our characterization of bacterial species as it does our definition of bacterial species. But, really, who cares? The article quotes Darwin: >I look at the term species as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other Which is essentially how scientists use it now. It's very convenient for categorization when it is, but often has no valuable meaning. You can (and should) say the same thing about the definition of life. Are viruses alive? It's an interesting question, but does it change anything? It's okay for some of the edges to be a bit blurry. The fluidity of "species" is, I think, one of the cooler aspects of modern biology. What better way to start teaching kids about evolution and the DNA that connects us all? 1: http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1000344 http://journals.plos.org/plosgenetics/article?id=10.1371/jou...

logfromblammo 11y ago

As a non-biologist, I'll just go ahead and suggest that species are defined by a single genetic exemplar that is an actual common ancestor to all extant members of the species. This individual then recruits additional members by hybridizing with its own ancestor species or sibling species in the same genus. Any given organism's species is determined by the relative genetic distance between it and the species exemplars. Under this regime, if we postulate a new species Homo superior with, for instance, the mutant ability to read and write text messages while also being fully aware of its surroundings, the earliest known bearer of the mutant gene would likely be chosen as the exemplar. If this person died and was not preserved in any way, we might be able to reconstruct a model of their genome via gene sequencing analyses, which would clearly show the mutant gene. It would hybridize with Homo sapiens, the parent species. Children lacking the mutant gene would be indistinguishable from H. sapiens. Children with it would clearly be able to trace lineage to the exemplar. Without barriers to breeding, the new species might just invisibly replace the parent species as a non-branching successor. In this case, we might just let it keep the same species name, and retcon the original mutation into the appearance of a subspecies. The fossil record makes selection of exemplars easier, because in many cases, only one instance even exists. Only one tooth found in Denisov cave. Only one Taung skull found. If there is no gene in Canis rufus that is unique to a single species exemplar, there is no unique species left. Even if it ever was its own species, having a purely theoretical exemplar with only a few known genes, right now it is just a lupus-latrans hybrid. So for me, a species would be defined by the presence of one or more specific genes. Those genes could be determined by sequencing DNA from actual remains, or inferred by analysis of living members of the species. Being able to interbreed fertile offspring seems to me to be more like a genus-level thing, because that seems pretty common in plants.