Right. Humans aren’t a “ring species”, we’re a just plain old ordinary “species”.
No, that’s exactly the situation that Chronos suggested. He proposed that the most distant populations (A and Z) at the farthest ends of the species’ range would be able to interbreed if they came into contact. That is the situation found in humans, as rather obliquely suggested by Sage Rat. The main difference is that human populations don’t form a “ring.” The initial major contacts between the most distantly isolated populations began with the European voyages of the late 1400s.
No. He was talking about a ring where there are intermediate species that can breed with each other but not breed with the endpoints (A and Z). There aren’t any human “intermediate species” that can’t interbreed with A and Z.
Admittedly the way he phrased it might not make it clear, since he didn’t specify the part about “… and species more than a few letters apart can’t interbreed directly,” but that’s pretty much understood when you’re discussing “ring species,” at least in the common usage.
Nope. Read his post:
Where does he say or imply that any of the intermediate populations can’t breed with the endpoints?
Not only didn’t he say that, that’s not what is “commonly understood” regarding ring species. The only requirement for a ring species is that the terminal subspecies not be able to interbreed; it says nothing about the situation between intermediate subspecies either way beyond the fact that adjacent ones can interbreed.
I think it’s clear that that’s what he was taking that to be an implicit part of the question, or else we wouldn’t even be talking about “ring species,” we’d just be talking about a regular ordinary species like humanity, where everybody can interbreed. For something to be relevant to a discussion of a ring species, there has to be a point where the subgroups can’t interbreed anymore.
Yeah, I tried to edit my post to change “more than a few letters apart” to “endpoints,” but it was too late. In any case, it’s clear that’s what he meant, and he has now verified that – the “terminal subspecies” in his question would be A and Z vs. M and N. Otherwise the question just makes no sense.
Let me clarify Chronos’s question using his terminology:
Are there any ring species that form a true ring, where A can interbreed with B, B can interbreed with C, … L can interbreed with M, M can interbreed with N (but L and M can’t interbreed with A and B) … X can interbreed with Y, Y can interbreed with Z, and hey, Z can interbreed with A. Thus forming an actual “ring” instead of a “chain.”
Sure, but that’s not part of the definition of a ring species. If you think differently, please provide a cite.
This is the situation that Mangetout described as a hypothetical, and as I have already pointed out it doesn’t fit the definition of ring species.
Again, if you think differently, please provide a cite to the scientific literature.
In case there’s any lingering ambiguity, I did indeed intend to imply that each sub-population would not be interfertile with populations a few letters away. And while I recognize that such a situation is not the standard ring species, it does seem to encompass the concept: If one didn’t know of the existance of populations, say, N through Z, then populations A through N could constitute a traditional ring (or likewise for any other way of breaking up the populations).
Regardless of what, if anything, it would be called; the hypothetical scenario I described above could only really occur by radiative diversification from a single point; for a true ring species to rejoin at the ends, it would require the restoration of compatibility, which is quite unlikely for organisms that have already diverged significantly.
To explicate a little further on this, it has often been assumed that populations of a species that are farther apart will be less likely to interbreed. This is in most cases imposssible to test under natural conditions, since populations that are far away are necessarily not in contact. It is only testable in the very rare case that a species has expanded until it entirely surrounds some geographical barrier and populations from distant parts ends of the range come into contact. The species does not necessarily have to form an actual ring.
As it turns out, most supposed cases of ring species have not been confirmed. Gene flow does in general prevent the acquistion of isolating mechanisms. It is isolation over time, rather than distance, that tends to cause speciation.
I was just clarifying what Chronos meant, not challenging your understanding of the technical definition of “ring species.”