Not so fast with the evolutionary fantasies. If they can breed and produce fertile offspring, are they really different species? Maybe we've got the definitions wrong somewhere.
> If they can breed and produce fertile offspring, are they really different species?
Species are defined more-or-less arbitrarily. It's essentially impossible to come up with a meaningful definition of "species" because of the nature of biology.
Imagine a gigantic tree, beginning with the first organism billions of years ago, with every living thing that ever existed as a node. Now, for the sake of the thought experiment, imagine that none of the lines ever died out.
There's no way to really consistently draw a line between one node and another and say "these are two different species." We pretty arbitrarily decide "well, these two sets are sufficiently different so let's call them two difference species." Like sibling commenters noted, sometimes hugely different species can interbreed and produce fertile offspring. Sometimes extremely similar (and related!) species can't breed. Or sometimes they can but never will except under laboratory conditions.
The article describes them as a different species — but doesn’t that mean we should not have been able to create viable offspring with them? What am I misunderstanding?
The definition of a species is not the inability to produce fertile offspring. Certainly if you can't produce fertile offspring then you are a different species, but having fertile offspring does not mean you are the same species.
Many humans (all non Africans) are a hybrid between two different species - all this result is telling us is that Africans and Neanderthals really are two different species.
> "In higher mammals the basic property of generating fertile offspring through sexual reproduction is clear-cut and undisputed."
What's undisputed is that there are plenty of species that can and occasionally will interbreed, and yet are still considered separate species. Wolves and coyotes, for example. Horses and donkeys are famous for producing infertile offspring, but occasionally, that offspring is still fertile.
So it's not a clear-cut on/off situation. There's a gradual scale from fertility to infertility. The edges of the old definition of species can get very fuzzy. For this reason, biologists these days tend to talk more in terms of populations than species.
Members of the same species can procreate fertile offspring. In some edge cases this definition becomes a little fuzzy, but it is clearly more than just a linguistic construct. A mouse and an elephant won't be able to procreate even if the word "species" didn't exist.
If we interbred with them, how are they actually species? It seems more to me you're talking more about racial or breed differences akin to breeds of dogs if two species actually successfuly had viable offspring in the wild.
My impression of defining species wasn't necessarily can they mate, but rather will they mate. Geography and sexual discrimination play as much of a part in separating species as does fertilization.
I still think it's super weird that they don't count as different species.
There's the suggestion that breeding + fertile offspring is the main concern, but couldn't early humans and neanderthals reproduce, for example? But we definitely consider them separate species.
It's true the same species implies fertile offspring, but it does not go the other way as you seem to be implying. In other words fertile offspring does not imply same species. For some examples, chihuahuas and wolves can produce fertile offspring, as can lions/tigers, killer whales/dolphins, and many more peculiar pairings.
It's quite difficult to pin down a precise definition for species. Even genetic definitions don't work so well. Depending on how it is measured chimps hit around 99% genetic similarity with humans. Nature isn't so kind as to provide clean and concrete delineations for us, at least not that we're currently capable of measuring.
Y'all should read the article. It goes into more depth than these two comments! For example, two species can have sex, AND produce viable offspring, but NOT produce fertile offspring. Like a donkey and horse producing a typically infertile mule. Horses and donkeys are not the same species.
I realize the concept of species is hard to pin down, but I thought one first-order approximation was that if two animals can reliably breed and form fertile offspring, then they are the same species. There are weird cases like ring species, and there is often a period of time during speciation where two lineages could functionally breed fine but don't because of some kind of ecological or behavioral barrier.
But if all these different human lineages apparently bred successfully and had fertile offspring (enough to leave a few percent of their DNA in modern humans), what is to say they were different species?
It's also just an extremely impractical definition. Say you have two animals and you want to know if they are the same species. How are you going to find out whether they can or cannot mate (and produce fertile offspring, even)?
What if they are the same species but just aren't that interested in each other?
Two individuals may be capable of breeding and reliably producing fertile offspring but still be considered different species if they would never mate "naturally". This may be due to geography, different mating seasons, different songs or appearances, etc.
In practice, that is often not the case. Most species haven't been tested to see whether they can produce viable offspring with each other(it's usually impractical), and there are plenty of different species known to breed successfully with one another. Mules, horse-donkey hybrids, while the vast majority of them are infertile, are considered different species. Camels and Llamas can produce viable offspring even though they evolved on two different continents.
To be pedantic about the fuzziness of the "species" delineation, not every human is capable of producing viable, non-sterile offspring (breeding partner notwithstanding).
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