Mol_PMB wrote: ↑05 Sep 2017, 17:27I got my head screwed up by all of this a couple of years back. A really important thing to remember is that 'Nature' does not recognise the concept of a species. 'Species' is an artificial invention by humans in an attempt to describe nature. It is useful, but it is over-simplified. The concept is rather 'black and white' where in fact nature is not just shades of grey but a full spectrum of colours, not all of which we can see.
As a biologist, I'd say that's both true and not true at the same time. It depends on what you mean by " 'Nature' doesn't recognize the concept of a species." It's true that humans invented the word and the definition (and therefore Nature doesn't need to recognize it), but using the Biological Species Concept, the definition is based on a measurable and quantifiable concept - the ability to share and exchange genes (and as a quantifiable concept, nature recognizes it functionally).
The biological species concept works pretty well when we ask about the ability to "successfully breed" among individuals
when those individuals live among groups of similar individuals and when they collectively form a contiguous range geographically: Those who can interbreed are in the same species and those who cannot are clearly not of the same species. But even this concept allows for the possibility that we get into what you might call subspecies (which I personally don't believe in as a concept), local populations/geographic variants (which I do believe in and which are probably closest to our concept of "subspecies"), and "interspecific" hybrid zones... You should expect these local groups in nature using this definition; in fact, they are the "stuff" of evolution and speciation - the mess that forms when existent species fracture and new species form. If these grey areas are robustly fertile, then I would argue they are within the same species but are local variants/color morphs. If their fertility is at all impaired, then I would argue they are interspecific hybrids or are at the very least local populations on the verge of speciation.
From what I last read, there is a trend to talk about local populations as "evolutionary units" independent of species as a whole. That makes sense, but from a logical perspective it does not elevate them out of the species or degrade the value of the species concept.
TwoTankAmin wrote: ↑05 Sep 2017, 17:16The best I can come up with here would be to consider Homo sapeins. All the humans on the planet are the same species now. But then we can find Watusi people who are extremely tall, pygmy people who are very small. We have people with black skin, white skin, eyes which are described as "slanted" etc. For the most part each sub-group tends to breed true, looks in some ways distinct from each other and is readily able to "inter-breed." So genetically we are all the same species but we do not all look similar. However, Homo sapiens seems to have become the dominant (lone) species of the humans.
Humans are a good example of the problem, as TTA mentioned above - There exists a great diversity of geographic variation in height, shape, color, etc. But there is so much migration that effectively the group of humans as a whole is a reproductively continuous unit, and that's why we consider ourselves one species. Gene flow between phenotypes prevents us from definitively saying one group (e.g., an African tribe) is a different species from another (e.g., a native North American tribe). But the very fact that genetic services like "23 and Me" or "Ancestry dot com" exist and can tell you (with some level of significance) your geographic ancestry affirms that there are genetic differences between groups of humans.
As to the issue of synthesizing the species concept for similar phenotypes that are widespread geographically but are classified as one species, the paper above helps to explain why this is particularly complicated with fish. I'm thinking of how fish are restricted (usually) by watersheds. It's tempting to think of a widespread morph like
Corydoras aeneus as one species, but if they are reproductively isolated by watersheds with little or no chance for gene flow between watersheds, then practically-speaking we probably need to bear down and say they aren't one species.
TwoTankAmin wrote: ↑05 Sep 2017, 17:16What I am drawing from all the recent discussions is basically nobody knows the facts yet. The one thing that apparently is known is that there is only one described B&W species in the Xingu, H. zebra.
I am a dunce re genetics. But it seems to me that the genetic research is incomplete, it is not sufficiently in depth to draw any conclusions. I even saw in the thread about the paper on 66 and 333 that some felt it was by no means conclusive due to the limits of what the researchers considered when doing their research. Or am I wrong on this?
The other issue that comes back to what TTA was discussing is that to date, since "biological species" are defined by reproductive isolation,
which can be satisfied by something as simple and tenuous as geographic isolation, then the definition does not have as a requisite a specific amount of genetic difference to quantitatively define two populations as separate species. And that's where the problems come in for things like L066, L333, and that whole mess.
In my opinion, this is not a fair statement since every other humanoid besides
Homo sapiens is based upon fossil evidence. So in terms of flesh-based phenotypes (skin, hair, etc.), they really have no type specimens either. If you are going to base type-specimens for all other humanoids on a skeleton, you could choose to do the same for
H. sapiens... But doing so masks our diversity.
TwoTankAmin wrote: ↑05 Sep 2017, 17:16This stuff is starting to make me sorry I ever moved beyond my first planted community tank
Dont be sorry - Complexity creates the spice of life! Without it, you wouldn't have H. zebra or anything else!
I'm sure others can take issue with my beliefs as stated here. And you're welcome to, since I don't consider myself to be the gold-standard by which species are defined. And although I'm an evolutionary biologist, I'm one only peripherally, not involved directly in the researching and writing up of work meant to advance our understanding of the concept of species and taxonomic units.
Cheers, Eric