Well this opens a can of worms.
There are more than one definition of a /species/. Species is a human
language construct that helps us define and explain what we are looking
at and what we are. Deciding what a species is, is not some concept
bestowed on us by "God" or some other god. So since we humans tend to
like to discuss various points of view (or sometimes argue them), there
are, in fact, different definitions of a species. Look up Biological
Species Concept and Phylogenetic Species Concept. While they certainly
have a lot in common, they definitely have differences in how they
define a species. A very good example of this is large white gulls of
the Genus /Larus. /What is a species in this group and what is not is
much debated.
So the definition of a species is somewhat fluid and subject to change
(and opinion, mind you, as there is no definite right or wrong, though
there is "more wrong"). The definition of hybrid, however, is a bit
more rigid, albeit that depends on whether we are talking birds or
plants. Sticking to birds, hybrid would mean two /species/ have
offspring. Whether those offspring are not viable however, is yet
another story. Some hybrids may in fact be sterile, but there are
plenty of examples of hybrids that are not (some wood warblers, gulls,
sapsuckers, etc etc). More closely related species tend to have fertile
offspring, more distant relatives will be more likely to be sterile.
What's important to remember is evolution is a process and is messy.
The ideas you are discussing are in fact humans constructs to help us
discuss these matters. Noah's comments are right on. If we hadn't
made the human decision to call these sapsuckers separate species, we
wouldn't be discussing whether any of these birds had mixed genes or
whether they are hybrids. But if we call them two different things,
and a bird has mixed genes, then it is a hybrid, but for our purpose as
birders IDing a bird, it is what it looks like. Ultimately a lot of
this is chasing our human words round and round.......
Cheers
Dave Lauten
On 3/9/2016 6:08 PM, Andy Thomas (Redacted sender adt0611 for DMARC) wrote:
It is my understanding that two individuals that can produce viable offspring are the same species by definition; and a hybrid is the offspring of two individuals of different species and is therefore /not/ viable. Am I mistaken? or have the definitions of /species/ and /hybrid/ changed? If there are different degrees of mixing, then the offspring must be reproducing in turn.
Andy Thomas
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*From:* Noah Strycker <noah.strycker@xxxxxxxxx>
*Subject:* [obol] Re: The continuing Sapsucker Dilemma
[...] I suppose this is a philosophical question of bird ID: When do you call a bird a hybrid? [...]
