> The definition of what constitutes a species is a human construct
That makes it sound like the boundaries between species are arbitrary, but they are not. Sure, there are corner cases where things become debatable, but those are the rare exceptions, not the rule.
> Two bird populations living in the same locale but divided by a mountain range therefore not naturally breeding with each other would classify as a different species, even if they could breed with each other.
This is only the case if the separation has been there long enough for the two groups to develop distinct genetic markers or physical traits (like the beak shape or plumage mentioned in the original comment). The deeper reason they are classified as different species it that they are de-facto on different evolutionary trajectories. Which doesn't happen for human populations because historically, whatever obstacle divide us, we find a way to get around it.
That makes it sound like the boundaries between species are arbitrary, but they are not. Sure, there are corner cases where things become debatable, but those are the rare exceptions, not the rule.
> Two bird populations living in the same locale but divided by a mountain range therefore not naturally breeding with each other would classify as a different species, even if they could breed with each other.
This is only the case if the separation has been there long enough for the two groups to develop distinct genetic markers or physical traits (like the beak shape or plumage mentioned in the original comment). The deeper reason they are classified as different species it that they are de-facto on different evolutionary trajectories. Which doesn't happen for human populations because historically, whatever obstacle divide us, we find a way to get around it.