Interspecies Mating

Neanderthals and so-called "modern humans" were of the same species. You probably should look into breeding animals. The offspring of animals that are of different types are different from either of the parents. Consider asses and horses, their offspring is almost always infertile (a sign that haorses and asses are different species), and the offspring look different from either parent.

As it happened Neanderthals were a regional variety of humans, not a different species, nor were they a different race (you might want to look up what "race" means in biology). Eventually, Neanderthals interbred with "modern humans" until there was no difference, and Neanderthal genes are carried by most present day humans.

There are forces trying to separate and other forces trying to unite species. You might want to read up on equines, horses and related species and how they have interacted over the years, especially with the interbreeding that humans encouraged. What you suspect as a possible outcome, three species, is unlikely based on what has happened with humans, horses, etc.

You probably should also look at what defines separate species. Generally, two types of animals are of different species if they cannot produce fertile offspring.

Maybe I'm reading it wrong, but it seems to me as if you've got the breeding thing backwards.

Setting aside the matter of how not being able to interbreed actually defines species (you don't calll it a new species until they have evolved far enough apart for that to occur), if humans and Neanderthals interbred, they'd produce sufficiently different hybrids pretty much right away. For the offspring to grow apart from their ancestral strains (us and the Neanderthals), though, those kids would have to breed entirely among themselves for a while, whereas breeding with humans (as you suggest) would just make their kids more human with each generation. Which is most likely what happened between homo sapiens and the Neanderthals back in the day. They got some of their DNA in, but we just kept evolving along our way by mostly sticking to humans since. (At least I never heard of anybody calling Europeans a subspecies.)

As for how long it would take for that secluded group to grow apart, think of Europeans and Africans. Granted, there are theories that claim we've never been that far apart for long, but Europeans and Africans parted ways thousands of years ago, and we're still the same species.

It depends on the pattern of mating (is everyone interbreeding, is it just people in certain geographic areas who are interbreeding). The problem is that it would very quickly become the case that you'd have 1 species, instead of 2 (or 3), if everyone is interbreeding. Their children would already essentially be neahumans. If you want three species, though, you'd want them to interbreed initially, but then for everyone to stop interbreeding and the children of those initial pairings to stick together and couple together.

But the bigger problem is the question of what defines a species--and frankly that's not a question anyone has ever answered. A traditional definition is that two individuals are members of separate species if when they mate they're offspring is infertile (if they can have offspring at all). So, A horse and a donkey can mate and produce a sterile offspring, a mule. (Well, actually, the vast majority of mules are infertile, but some actually can have kids. And it gets a bit weirder because mules are the children of male donkeys and female horses. The children of male horses and females donkeys are hinneys, they're much harder to produce, and they are, apparently, always infertile).

I don't know how easily humans and neanderthals mated, how fertile their offspring were, etc, but by at least one common but (obviously deficient) definition, they are already members of the same species.

So the answer to your question really depends on what makes a species for the characters and society in your world. If we're talking about these neahumans being some sort of societal outcast, then you don't need to worry about the realities of biology, for instance.

If you're wondering about the new species having distinct traits, maybe even traits that aren't common if they exist at all in their parent species, you need to have the force of evolution acting over time to produce those (and remember that the parent species would also continue to evolve).

As far as a time scale, that can vary, and it really depends on mating patterns. At the extreme end of the scale are subspecies like the domesticated silver fox (though it doesn't involve interbreeding). This was/is a Russian experiment to tame foxes to domesticate them in similar ways to how wolves were domesticated into dogs. It turned out that it took about 50 years and as many generations to produce from wild animals foxes that were as tames as they could breed them (and they're now sold as pets to support further research). They would still interbreed with regular foxes I expect, but they're very different from their wild ancestors.

For comparison, if a human generation is about 20 years, it would take maybe 1000 years to deliberately breed a single trait (though differences were apart after far fewer generations). True speciation, especially without a deliberate breeding program, would take far longer.

So, it really depends on what your world means by species, what the generation lengths are, how much interbreeding takes place and so on.

There's a long, very interesting article on this very subject in this week's NY Times Magazine: Should You Fear the Pizzly Bear?

At the extreme end of the scale are subspecies like the domesticated silver fox (though it doesn't involve interbreeding). This was/is a Russian experiment to tame foxes to domesticate them in similar ways to how wolves were domesticated into dogs. It turned out that it took about 50 years and as many generations to produce from wild animals foxes that were as tames as they could breed them (and they're now sold as pets to support further research). They would still interbreed with regular foxes I expect, but they're very different from their wild ancestors.

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One of the fascinating things about this experiment is that the experimenters started with a group of completely wild foxes and bred them selectively for a single trait:allowing humans to handle them. (The first few generations: hardly any handling possible for any of them.) After enough generations passed, the breed of foxes that emerged had a lot of characteristics that were never expressed in their wild ancestors but are very, very similar to what you see in domestic dogs: coat (texture, color & patterns), neotenous proportions, barking, sociability, etc. -- all very doglike, not at all foxlike, but they are still purebred foxes with no dog in them at all. The theory I've seen comes down to it not being a change in the genome itself, but in the developmental timing that switches different genes on & off, which is coincidentally linked to a whole cluster of traits in addition to the behavior that's being actively selected for.

Take a look at all the breeds of sheep. They come from the same ancestor but both through design of their shepherds and local conditions there are massive differences in size, shape, horns, no horns, colour of wool and texture of wool.

For interbreeding to work, the two breeders would have to be the same species, as someone already mentioned. There is the possibility of having a subspecies, however, that is physically different. This occurs when a portion of the population is cut off from the main group and evolves independently for a long period of time. It's a step in the process of developing an entirely separate species. For example, there are several subspecies of tiger that developed because of geographic isolation. This is a direct result of inbreeding.

What I think you are talking about is not evolution, it's more like selective breeding. This is a process farmers use to produce animals (or plants) with the most desired traits. This is how the various breeds of dogs were produced, all from the original wolf ancestors. You take a dog that has a trait you like, and breed it to another dog with the same trait. The offspring should share the trait. Then you take those offspring and pick the best examples of the trait and breed those offspring. For example, if you wanted a dog with really short legs, you'd pick the breed that was closest to what you were looking for, then pick the individuals with the shortest legs and breed them. In several generations, if you do it right, you'd develop something like a corgi or dachshund. Technically, these pups are still breedable with wolves.

The problem with inbreeding, though, is that not just the desired traits are concentrated. Look up inbreeding and you'll find all kinds of references to things like hemophilia and other genetic diseases. The Vadoma tribe of Zimbabe is known for having two-toed feet because of inbreeding.

King Neptune said:

You probably should also look at what defines separate species. Generally, two types of animals are of different species if they cannot produce fertile offspring.

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Actually there is evidence that Neanderthal's may have been a separate species as genetic evidence has led to a new slant on Human/Neanderthal procreation.

It seems that the Male offspring may have been sterile whereas only the female hybrids could reproduce. This puts Neanderthals and Homosapians at the far, blury end of the species continuum.

http://www.geneticliteracyproject.org/2014/02/04/were-neanderthals-a-different-species/

In my understanding of this, the sons of a female hybrid would not be able to pass on their Mitochondrial DNA to their offspring (the grandchildren of the hybrid). So the female generations would carry more Neanderthal DNA in that scenario.

You're really talking about inter-racial breeding. With that in mind, you might look up the history of Brazil. Black, white, and brown people have been mixing themselves together in Brazil since the 1500s. An official mixed-race skin color named 'Pardo' came into use in the 1800s, about 300 years after the first settlers. That might indicate how long it took society to notice the new look of the younger generations.

Note that Brazil and its mixed-race heritage was built by waves of people -- first the Amerind, then a wave of Europeans, then a wave of Africans, etc. You might expect your fictional country to have a similar history.

Paramite Pie said:

Actually there is evidence that Neanderthal's may have been a separate species as genetic evidence has led to a new slant on Human/Neanderthal procreation.

It seems that the Male offspring may have been sterile whereas only the female hybrids could reproduce. This puts Neanderthals and Homosapians at the far, blury end of the species continuum.

http://www.geneticliteracyproject.org/2014/02/04/were-neanderthals-a-different-species/

In my understanding of this, the sons of a female hybrid would not be able to pass on their Mitochondrial DNA to their offspring (the grandchildren of the hybrid). So the female generations would carry more Neanderthal DNA in that scenario.

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My understanding is that the biggest problem that the group that sequenced Neanderthal DNA had was separating it, finding differences. There is considerable fossil evidence that there was interbreeding between Neanderthals and other groups of humans, and that the offspring were fertile, as is further evidenced by the fact that Neanderthal DNA has remained in the human genome. That article appears to support that position, and it seems to suggest that some parts of the human genome were taken wholesale from Neanderthal, while other parts were not.

I worked in a genetics lab on species hybridization. There are species out there that can fully interbreed (mostly marine and, far as I know, entirely invertebrate (that we know of!)), and others that we'd call a single species but populations cannot be convinced to mate, which makes the point of if it's viable entirely academic. This shows just how blurry our definition of "species" can be, and anything could feasibly work.

As far as the look, you'd see a very dramatic range in the first generation or two, but if the hybrids just kept breeding with the hybrids, the usual look would steady out. However, unless the interbreeding event happened once and then one or both original species left, the interbreeding could just keep happening. A hybrid could breed with one of the smaller species, producing offspring only a bit more bulky than the usual small phenotypes (with the odd giant thrown in as genes scramble and remix), or vice versa with the Neanderthal-like ones. If they live close enough that this is common, I'd expect both original populations to start showing more traits of the other one rather than expect a unique third population.

As mentioned above, look at racial mixing in places like Brazil to see examples of this within a single species.

The thing they teach about infertile offspring is an over-simplification for school children. Mules are used as an example because they usually fit. All the hybrids that don't usually fit don't get taught at school. Species is complicated. Whether hybrids can breed, and who with, is also complicated. (As you might guess, I'm not a fan of the way they teach species at school... it could be simplified without being given as this cast-iron definition that turns out to be a lie when you study biology further).

So I'm going to send you to Wikipedia, as it has a bunch of hybrid examples, some discussion of different types, and a references list. http://en.wikipedia.org/wiki/Hybrid_%28biology%29

It also has a page on hybrid speciation, where the hybrids achieve reproductive isolation from the parent species: http://en.wikipedia.org/wiki/Hybrid_speciation

And you can read up about why species is not a simple one-liner definition: http://en.wikipedia.org/wiki/Species

Usual warnings apply to check out the sources and don't assume it's entirely accurate. But I think it's a good starting point.