A randy group we were, apparently. This article claims interbreeding with at least 4 other species.
Interesting.
https://www.google.com/amp/s/www.inverse.com/amp/article/58180-ancient-human-sex-death-babies
If humans could breed and produce viable offspring with them, were they really different species?
I didn’t really just say that.
An interesting point. I don’t know but it’s claimed by the article.
How on earth can they match up Neanderthal genes with tobacco addiction??? And malnutrition? Junk food addiction too???
Sure. Hybrid offspring are not always infertile. Some of the more common modern examples (such as the mule) are typically infertile, but that is not true of all mixed-species offspring.
Well, we are descended from Homo erectus. 
I wanted to mention in a different thread that Carol Post and Mr. Ed were TV’s hottest couple.
The biological species concept rests upon reproductive isolation. Reproductive isolation may be due to physical separation, lack of actual interbreeding, not necessarily the potential to produce offspring (viable or otherwise) if they do meet and mate. Although if two populations are separated long enough they will inevitably eventually diverge far enough that they cannot interbreed.
Here we’re talking about marginal cases. Populations that were separated completely or almost completely for long enough that genetic divergence was considerable, sufficient that any gene can be identified as (for example) the version prevalent in the Neanderthal population. But the divergence was not yet so great that they could not still, on rare occasions, mate and produce viable and fertile offspring.
I’m just wondering where species stops and race begins. Why are Neanderthals, Denisovians et al separate species and not just separate races? So some people back then were smaller, and some had heavier bones - people today have different skin color, but we’re all still the same species.
I’m not a biologist, at all. But I thought that defining species by subjective factors like physiognomy or location was the “old” biology, and that “new”, post-gene mapping biology was all about genetics, and genetics only.
I gaze back at my cactus-mapping days. Chollas (cylindropuntias) and beavertails (platyopuntias) share a tribe containing varied genera; they don’t normally hybridize. Platyopuntias native to Central America and California are distinct genera but hybridize quite vigorously, forming fire-resistant pockets, any one of which hosts enough DNA complexity to generate several doctoral theses.
Or note the Rosaceae, which family includes many tree fruits (apples, pears, peaches, plums, quinces, cherries, apricots, almonds, etc) as well as roses, raspberries, and strawberries. Although different species, many are readily hybridized, naturally or with human help.
Moral: male pollen floating about will fuck any receptive floral ovary. Anthropoids are no less selective.
Race isn’t an entirely biological concept. Defining what exactly defines a species has been tricky: Species concept - Wikipedia
That doesn’t mean the term isn’t useful. But it’s fuzzy around the edges.
Nothing I wrote is remotely about “defining species by subjective factors like physiognomy or location”. I am talking about genetics.
By divergence, I mean genetic divergence, although this obviously implies phenotypic differences.
I wasn’t talking about defining species by where they are located, physical separation is important to understanding the process of speciation. Physical separation is the most obvious path to reproductive isolation and cessation of gene flow between subpopulations.
There’s no strictly defined point at which two populations become different species, there will always be marginal cases. “Race” is used by some biologists, but it’s not a particularly important or qualitatively well-defined term. We have species, subspecies, race, strain - indicating varying levels of genetic divergence without a bright line between them. Well, okay, ultimately speciation mean no gene flow, and I suppose that’s qualitatively different from some gene flow.
What are the circumstances that determine whether hybrids can be fertile?
As I have understood it, the answer has to do with the number of chromosomes. If Mommy Parent and Daddy Parent are of species that have the same number of chromosomes, then Hybrid Baby can be fertile. If not, then not.
This happens because, if Mommy and Daddy have different numbers of chromosomes, they can’t pair up properly to make a viable fertilized ovum. (That is, they can produce a hybrid offspring, but that offspring will have a mixed chromosome structure that doesn’t work for creating further offspring.) Nonetheless, the Wiki page for Mule mentions that mule pregnancies, while very rare, have been known occasionally to happen.
(This doesn’t address the obvious related question of what circumstances make hybridizing even possible.)
Whadaya mean, were?
Different chromosome number is sufficient, but much less dramatic changes can cause hybrid incompatibility. The challenge is to explain how a negative fitness effect is not selected against. If a mutation is deleterious, it will usually be removed from a population by purifying selection. So the idea is that in reproductively isolated populations, mutations can arise at different loci, each of which alone is harmless, so they are not subject to negative selection and may proliferate. But when present together, something that only ever happens in a hybrid, the combination of two or more mutations is harmful.
That’s what I said about dogs and wolves. Apparently, the answer is yes.
I don’t think there’s any objectively correct answer to whether wolves and dogs are the same species today. This is similar to the situation described in the OP. Reproductive isolation is behavioral, i.e. they do not interbreed in practice (except rarely), even though they could, so there little to no gene flow between the two populations, which leads to increasing genetic divergence over time.
They diverged about 30,000 years ago, not very long in evolutionary terms. So the best we can say is that we might now be in the process of a speciation event. There are several possibilities for the future. If the current situation continues, with no gene flow between the two populations, the populations will eventually inevitably accumulate enough divergent genetic loci with hybrid incompatibility to make offspring infertile then nonviable. At that point they would clearly be two different species. Alternatively, perhaps in some dystopian future where humans disappear and domestic dogs roam wild, the two populations might start to interbreed and merge back to a single panmictic population, one species; or they might compete for the same niche without interbreeding, driving one population extinct.
These days they’re considered the same species -* Canis Lupus (familiaris)*
Probably as many in Africa, too. At least as divergent as Neanderthals. Some rather sensationally late. Paper should be out soon.
It seems that Europe had an unusually turbulent history in these matters. In Africa and eastwards in the worm regions, people seemed to colonize and area and then stick to it for vast timespans without that much interaction with neighbors. Europe during the Ice Age was basically a very marginal peninsula that seems to have suffered extinctions and repopulations several times. And after Anatomically Modern Humans arrived, seemed to have a number of refugia where populations could be isolated.