From: Bill Lucy 

In article , email{at}from_Gary_Britt.org says...
> Think about it.  Its an implicit assumption.  Each bird in the series can
> only mate with a next door neighbor and you move around a circle in a single
> direction.  Of course, this implies that the birds only fly/migrate in one
> direction and not in all directions at once.

You infer something not in evidence. It happens that a specific ring
species might not interbreed with its neighbor at the "other" end
of the ring, but it is not impossible, or even improbable.

Such would depend upon such things as the size of the ring. It makes sense, really.

As to directionality, that makes sense too. The factor which makes the ring
necessary and sufficient is what causes the ring effect to occur.

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