This might not be a real GQ question as it might not have a definite answer. If not then mods, feel free to move it.
My question is…how long would it take for a small isolated population of humans on an extra-terrestrial planet to speciate? Some background setup for the answers. Let’s say that humans do eventually figure out how to venture to the stars. No warp drive or worm holes, but we do figure out how to achieve, say, .5 C speeds and the ability to put humans and other animals into some sort of suspended animation. It’s still a VERY costly proposition, but it’s something we can do with great effort. Further, let’s assume that we have found a number of planets within, say, 50 light years of the Earth that can be terraformed to allow humans and other Earth based life to live and thrive on them. Since interstellar travel is so expensive, we can only send a small human population and limited other species (plants and animals)…just enough to start a colony that could be viable.
So, back to the question…once established, how long would it take for these relatively isolated groups to speciate from the main body of humans back on the Earth? How long would it take to begin developing distinctive breeds or races that could still breed with the main body of humans but were distinctive from all breeds currently in our population? Assume that once established these colonies would be on their own without contact with either the other colonies or the Earth for as long as you like to answer the question.
Speciation among mammals is very problematic, and there is no general agreement on what constitutes a species among most genera of mammals. Unlike birds, whose species are pretty well set, with little or infrequent argument among ornithologists about the separation of species.
Furthermore, speciation is generally defined largely according the the ability of individuals to mate successfully with viable young. An isolated culture of Homo sapiens would not be declared a species until it was shown that inter-breeding would not occur. Which, under the conditions described, would never happen.
It would depend on what kind of challenges the new environment presented. If the environment were so carefully like earth-- if we somehow sterilized it, and then introduced only earth bacteria and viruses, it would take longer. If the gravitational pull required modification of human musculature, and if the landscape required different kinds of buildings and vehicles than the ones we use now, that might give an advantage to a body type that is unusual here. If something that exists in abundance on the planet is edible, but only to some people (some people have the equivalence of celiac disease in response to it, other people find it highly digestible), then some people suddenly have a huge advantage. If the average temperature is 10’F lower, that might be a disadvantage to very thin people, who might have shorter lifespans.
If we don’t sterilize it, and somehow, there is an infectious agent, particularly one that doesn’t kill, but that we can live with, that can alter our bodies greatly.
If Stephen Jay Gould is correct about punctuated equilibrium, it might not take very long, in geologic terms, like a few thousand years, for a new species, but then there would be no more change for millions of years without a change to the environment.
But that would depend, as someone else said, on how you define species. It’s possible you might have a hominid creature that could mate with H. sapiens, and produce sterile offspring. There are lots of distinct species that can still produce offspring. H. sapiens & H. erectus could probably produce offspring, maybe even fertile ones, but are still considered separate species.
OK, first off there are no “breeds” of humans. And there are no scientifically defined races, either. If you want to ask how long will it be until a population develops distinctive traits that set them apart from other populations, that’s a question that might be answered, but it depends on just how different they need to be and how determinative your test of the difference is.
As to the larger question, it’s generally thought that it takes on the order of 1M years for a large mammal like H. sapiens to speciate, lacking any catastrophic change in the environment. And given our slow reproduction rate, it would probably take longer.
But really, there is no answer to your question as there is no standard rate of speciation.
Here are some of the factors upon which it would depend:
-The selective pressures on the new planet
-The size of the founder population
-The genetic makeup of the founder population: how much variation exists, and where that variation is vs the original population
-Your working definition of “species”
-The mutation rate on the new planet. Different stars could have different radiation profiles that could increase or decrease mutation rates vs Earth.
So would that 1M year figure be the estimate through genetic drift? I can well believe that - given enough time - a human population would speciate simply through drift if totally isolated. I’d have thought it would take more time, though.
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OK, first off there are no “breeds” of humans.
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I guess it depends on how you look at that term. Certainly we haven’t been intentionally bread for different traits. However, there are diverse populations that have superficial traits that are different than other populations yet can still interbreed. No idea what the ‘correct’ word for this is, so went with breeds since it seemed the closest. Feel free to correct my ignorance by providing the correct term.
Why yes, I know this. But the term races is like the breeds term…an attempt to convey the fact that you can have populations that have distinct traits from other populations but can still interbreed (i.e. it’s still one species that can fully interbreed but still have their own distinctive traits, some superficial, some not).
Leaving aside the semantic discussion, that’s exactly what I was asking…well, that and how long it would take (generally, not precisely) before the populations would diverge enough to become completely separate species. If the later question can’t be answered in GQ then that’s fine…the Mods can move it or someone can put forth a less than precise answer (a ballpark would work, or even an informed guess). As for the former, I guess it would depend on if there IS a current term for different human populations. From the semi-hostility I’m picking up from your first answers I’m guessing the answer is ‘no’…there is no term for how scientists group different human populations into distinct groups, even if there are broadly similar populations that have traits that are different than other human populations.
Ok, that’s fair enough. I wouldn’t have thought it would take that long for full speciation, but I assume you are basing that on our own probable time line for when H.S and H.N split?
No, I didn’t figure there would be a standard rate, but was hoping for an educated guess or ball park. I realize this is GQ, but that doesn’t mean a question can’t be asked that doesn’t have an exact, precise answer, as long as the answer is based on good science. Your approx. 1 million year answer is what I was looking for…something based on fact that gives a good baseline.
Just so you know where I was coming from on this, I’m reading a book about humans and elves living on the same planet. In this book, the humans and elves can interbreed and produce viable offspring, despite the effort of the author to say they are distinct species. To me, this is incorrect…if the humans and elves in the book can interbreed and produce viable offspring (who can also breed) then they are essentially the same species with just distinctive traits. Extrapolating from that, I was thinking what it would take to get to that level…two human/elf breeds (or whatever you want to call them) who were completely able to interbreed and produce viable offspring who could do the same. And I thought maybe if you could separate them to distant planets that were extremely difficult to get too for a long enough time that you’d get the situation in the book. Then I just wanted to know how long you might have to keep them separated to get full on different species. Thus, the question.
Well, the population size would be small…basically, the smallest population that would be viable (this would be the same for any other species we also brought along). I’d guess something like 2000 (1000 male 1000 female) individuals IIRC correctly.
As for the make up of the population, you can use whatever assumptions you’d like. My GUESS would be that it would be a nation state that would do something like this, or a coalition of nation states…so, maybe representatives from the US, Europe, China, India, Japan and maybe others. So, we could start off with a fairly diverse if very small population. Most likely they would be selected initially for good health and no genetic diseases or defects.
My non-biologist working definition of species is when two populations can no longer interbreed and produce viable offspring or offspring who can not breed true. I’m not a biologist, however, so if you want to offer a better, more concise or accurate one I’m all ears. Same with the issue of ‘breeds’ or whatever they are called, assuming they are called anything at all.
I don’t know about the mutation rate answer since it’s going to vary widely. I’d go with approx. the same as Earth just because that will allow a more precise answer and the fact that if we are colonizing new planets they will have to be within certain tolerances of this planet to make them viable possibilities for colonization.
As to selective pressure, I assume that colonizing an alien planet is going to put a lot more selective pressure on the humans there than the Earth does, especially early on in the colonies life. It’s going to be tough and difficult and a struggle with such a small initial population and cut off from all aid from the Earth and on their own.
It’s kind of a strange combination of a small isolated population starting with broad genetic diversity as a result of the international makeup of the founding population. If the population grows rapidly the genetic diversity will increase over time and some kind of bottleneck would be needed for rapid change to occur. Environmental changes or disease could easily reduce the diversity allowing subsequent mutations to spread more rapidly through the population. Without a bottleneck like that the million year figure above is a reasonable guess if for no other reason that it’s a very long period of time allowing for more opportunities for a change to occur and propogate through the species.
This is certainly not true with respect to birds. Avian taxonomy at the species level has changed greatly in recent decades. Genetic data and changing concepts of species have affected classification in all groups, not just mammals. Even within mammals, differences in classification are produced by different taxonomic philosophies, not really on whether the populations are related at some level.
Not really. According to the Biological Species Concept, species are defined based on whether they regularly produce viable young in nature, not whether they are capable of doing so. Many good species are fully interfertile with others.
This doesn’t follow. A small population under a very high degree of selection could certainly speciate given enough time, even under the condition of requiring infertility.
Humans and elves might be physiologically able to interbreed, but maybe 99% of elves will look at a human and say “Eww, no way am I going to sleep with that thing”. If that’s the case, then it might still be justifiable to call humans and elves separate species.
Or maybe it’s the humans rejecting the elves, or both, but elves rejecting humans seems more typical for fantasy literature.
the humans who came out of Africa and occupied Europe and central or northern Asia appear to have lost their skin darkening (melanin) in a matter of 50,000 to 100,000 years and developed different facial characteristicfs, to some extent due to selection from climate. The aborigines of Australia are relatively distinct but not a lot different after 40,000 to 50,000 years. the natives of America are not very distinct from southern Alaska to Tierra del Fuego in 15,000 years or less, and very similar to Siberians. While there was a minor amount of mixing happening along the chains, none has become a separate species. Pehaps the closest we come to distinct would be something like the pygmy tribes.
So that gives us some boundaries - under uncontrolled pressure, living “in the wild”, probably 50,000 years to become fairly distinct and a lot more than that (half a million to a million years?) to become not regularly inter-fertile?
Of course, it depends on the environmental pressure. With air conditioning and plenty of indoors and skin cancer medical care, european Australians or Floridians or South Africans are going to take a lot longer to adapt to their climate than the original inhabitants. Eskimos have a more significant layer of fat to deal with their cold climate. We have central heating and cars with heated seats. Change will be much slower.
As for two “specie” mixing - once they do and habitually do, it does not take much time for the population to be a smear of mixed genes. South Africa and the American south had a distinct society of mixed-race people despite disapproval from the dominant society, and that was only about a century or two; and the society was only dsctinct because one group could impose it’s severe disapproval on the other… and that was where the mix was extremely obvious.
Plenty of genuine species can cross-breed and produce “viable” young if you define “viable” as being able to grow up and live a lifespan comparable with the parent species. For example: mules. Perfectly viable offspring of a horse and a donkey, but with extremely rare exception (and always female when it does happen) sterile. Then there are lions and tigers - they don’t seem to interbreed in the wild, but have done so in captivity.
So… if hypothetical elves and humans were able to produce offspring, but that offspring was sterile, they could be defined as separate species. If they could reproduce, including offspring that aren’t sterile, but very seldom do so, like almost never, and retain very distinctive traits/ecological niches they might still be defined as separate species.
At present, no population of humans is so distant from the rest in either traits or anything else that they could be called a separate species. The last time that state of affairs was the case was before the Neanderthals died out (mostly - apparently there was sufficient interbreeding some of their genome survives in present humanity).
As for how long it would take - that depends on many variables. Isolation and a radically different environment are going to speed up the process of diverging into separate species.
Many good species, such as wolves and coyotes, are fully interfertile but maintain their species identity even where they co-occur due to behavioral and ecological differences that minimize hybridization. (However, it has been found that some populations have considerable genetic admixture from the other species.)
With humans such behavioral barriers to mating are problematic as species criteria since they are largely cultural and thus relatively easily overcome. Even in cases where there have been strong taboos against interracial mating, and cultural norms that regarded another race as ugly and unattractive, there has been extensive mixing.
Yes, probably. But I also think that humans present some problems for the Biological Species Concept, since it relies on what happens “in the wild”. We hoo-mans will mate with almost anything if we have the whim to do so, and it’s hard to imagine (per Chronos’s suggestion) that there might be two populations of us that wouldn’t be inclined to mate with each other.
The term “breed” is generally used to denote a population of animals that have been bred for certain traits and in order to be included in that “breed” you have to have a perfect pedigree and be recognized by some organization set up to decide this sort of thing. That situation doesn’t exist for humans.
Best to use the term “population” if you want to define some sub-group of humans.
But the term races is like the breeds term…an attempt to convey the fact that you can have populations that have distinct traits from other populations but can still interbreed (i.e. it’s still one species that can fully interbreed but still have their own distinctive traits, some superficial, some not).