Not true, as species are usually described. Lots of separate species can and sometimes do produce fertile hybrids. Almost every species of duck is known to produce hybrids with multiple others, for example. All that’s needed for separate species (using the popular biological species concept) is that there is some genetically-based mechanism that prevents two populations from merging. This could be hybrid sterility, but it could also just be that hybrid offspring have less reproductive success than non-hybrids for whatever reason, perhaps that they don’t do quite the right courtship rituals, or that they don’t look attractive, or that they are for some reason a bit less fertile. And this highlights the problem with Bill’s criterion: interbreeding is not a binary state but a continuum. As we expect if new species evolve by splitting of populations.
[Added: I do wonder how Bill would deal with Haldane’s rule.]
I figured there would be more nuance to it than the quick interfertility sound bite, and for the purposes of the argument at hand, there may not be a need (yet?) to get all so precise about it. Still, better be accurate now than to look like we’re shifting the goal post later. Also, ever grateful for any bit like that I learn. So, in that spirit: Thank you for the correction.
Interbreeding is a not a characteristic that is necessarily exclusive to common ancestry.
If you allow for a created population of individuals capable of interbreeding (as part of an independent origin event), then interbreeding necessarily can’t be exclusive to common ancestry.
Therefore interbreeding cannot be used to distinguish organisms that have been created versus those that have arisen from prior ancestors. You need some other criteria.
I’m using the term “interbreed” to refer to individuals of a population breeding with one another (per the Merriam-Webster dictionary definition). I am not exclusively referring to breeding between species, although in principle interbreeding could potentially include that as per examples listed previously in the discussion.
I think I see the disconnect. I agree with you there is common ancestry. The question is how extensive it is. If the population in question is able to interbreed then I would agree with you they share a common ancestor.
The question is do they share a common ancestor with a population they cannot breed with.
But that’s not the question, because you haven’t established that inter-fertility between individuals or populations is an exclusive characteristic of common ancestry.
Because we’re trying to distinguish between organisms that have arisen from an “independent creation event” versus organisms that originated via reproduction and common ancestry.
Therefore you need to identify characteristics of an independent creation event and/or common ancestry that are exclusive to each in order to distinguish them.
Can we start with a chicken and a mouse? Is it reasonable to ask if they come from a single common ancestor in the past or are the from separate points of origin.
I have a better idea: let’s start with a chicken and a chicken.
Can you provide criteria that can demonstrate that these chickens share common ancestry and are not the result of independent creation events?
And if your answer is, “if they can interbreed they share common ancestry”, you need to first demonstrate why a creator couldn’t create multiple separate chicken populations capable of interbreeding.
And if you can’t do the latter, then you can’t demonstrate that interbreeding is exclusive to common ancestry and we’re right back to where we started.
Or, pretty please, can we start with Shakespeare and me? Shakespeare is so special (in some peoples’ minds, anyway) that an entire scholarly subspecialty is devoted to identifying the “real” author of his works, since it is apparently obvious to these people that only some kind of genius (god?) can suffice. My point being that it is “reasonable” in some settings, perhaps helped by beverages, to suggest that he was… what’s the technical term… oh yes… independently created from a “separate point of origin.” And why not?
You are asking how they can be related by common ancestry if they do not meet your personal criteria. Criteria that, as everyone here is trying to expalin to you, are nonsensical.
How would you quantify the likelihood of a creator creating independent populations of chickens capable of interbreeding with one another, and that descendents of those populations are not related via common ancestry?
How would you do that without quantifying the likelihood of separate origin of chicken populations? How would you do that, period? And what are “both cases”?
Hi John
We don’t need to quantify the likelihood null hypothesis. We simply need to quantify the likelihood of a reproductive connection between the targeted species. If the species can mate with each other the likelihood of a reproductive connection is much higher than if they cannot.
That doesn’t work because that doesn’t address the scenario of a creator creating a bunch of individual populations of chickens that can interbreed with one another. For all we know, the creator could have created a million different populations of chickens, and there are a million different ancestral populations.
You’re still stuck on this notion that interbreeding somehow demonstrates common ancestry while ignoring the fact you have no way of assessing the independent creation of populations that can interbreed.
