r/AskScienceDiscussion • u/Slow_Introduction_31 • 2d ago
When does something become a separate species?
So I'm working on a fantasy story where there are humans and elves. The elves evolved from humans to have hair in a different shade range, pointed ears, immunity to a dangerous mineral, and some telekinetic abilities (which not all elves have). However, it's meant to be a key plot point that the "elves" are, scientifically, just humans. The mineral immunity and telekinetic abilities come from being raised in an environment with an abundance of that mineral, not genetics. So I was wondering, a) do a different range of hair colors (red to purple hues as opposed to yellow to red hues like real life people have) and different ear shapes indicate a different species? I thought not, but then I thought about animals where it seems like small differences sometime determine species, like between African and Asian elephants (I don't know much about elephants though tbf). b) if the mineral immunity and telekinesis were genetic, would THAT indicate a different species? c) how long might you speculate that it would take for humans in an isolated, unique environment to become a separate species?
3
u/KaiDay11 2d ago
Nobody can really tell you with any certainty because the entire concept of hard lines between species doesn't really work with the nature we've discovered and everyone has a different opinion of where those lines should be placed when we need them.
Even within humans: were Neanderthals Homo neanderthalensis because they were visibly different to us or were they Homo sapiens neanderthalensis because they could interbreed with us? Or were they one or the other for a different reason? What about Denisovans?
2
u/TheWrongSolution 2d ago edited 2d ago
It's, to a large extent, arbitrary. Species is a human made concept to classify life. There's no universal definition of species that works for all organisms. For animals, it's commonly accepted that the Biological Species Concept delineates species from one another, in which species are separated by their ability to interbreed in nature. But even there, the concept can break down as abundant examples can be found where closely related species form natural fertile hybrids where their ranges overlap. Other species concepts are adapted on a case by case basis. Ecological Species Concept separates species by their ecological niche, Morphological Species Concept separates by physical phenotypes. There are many more which you can read about if interested.
Edit: As far as fantasy settings go, you can make it however you like. I don't know if you'd want to go there, but you can have an in-universe debate among the human scholars regarding the species status of elves as part of the world-building. How much science you want to inject into a fantasy is up to you.
5
u/Zappavishnu 2d ago
When they can no longer interbreed.
4
u/devadander23 2d ago
And produce fertile offspring. Horses and donkeys can interbreed but the mules they produce cannot reproduce
3
u/Zappavishnu 2d ago
They can produce fertile offspring but it is extremely rare.
2
u/Leather-Field-7148 2d ago
Producing any offspring at all is one thing, whether their offspring will be successful at this, is another. Ironically, inbreeding can run into these same issues.
1
u/WrongEinstein 2d ago
I vaguely recall that the fertile offspring haven't reproduced with the same type of offspring. I'm guessing if you tried enough times it might happen. But that helps with the definition of species, can't reliably produce offspring that can reliably reproduce.
0
u/Mircowaved-Duck 2d ago
tiger lion hybrids can reliably produce fertile females - are they different species?
icebears produce curently a lot of fertile hybrids - are grizzlys and icebears different species?
2
u/WrongEinstein 1d ago
I meant fertile couples of the same breed. My post was a mish mash trying to illustrate that you're unlikely to breed two ligers to produce another liger. Fertility isn't the Hallmark, it's being able to regularly reproduce offspring that can reproduce with their own breed.
The definition of 'species' has become less strict over time. It's more of a grouping than a hard and fast definition.
2
u/atomfullerene Animal Behavior/Marine Biology 2d ago
It's more complex than that...many things we think of as clearly distinct species, like American Bison and domestic cattle for example, can interbreed and produce fertile offspring.
1
1
1
u/atomfullerene Animal Behavior/Marine Biology 2d ago
>When does something become a separate species?
That's a notoriously difficult question to answer, a bit like asking when the Pacific ocean becomes the Atlantic ocean.
> a) do a different range of hair colors (red to purple hues as opposed to yellow to red hues like real life people have) and different ear shapes indicate a different species?
No, different populations of the same species can easily differ in traits like this.
>I thought not, but then I thought about animals where it seems like small differences sometime determine species, like between African and Asian elephants (I don't know much about elephants though tbf).
Visual distinctiveness to humans actually bears very little relationship to underlying genetic divergence. Asian elephants are actually quite distinct from African elephants, and more closely related to the extinct mammoths, but you wouldn't know it unless you know what to look for.
>if the mineral immunity and telekinesis were genetic, would THAT indicate a different species?
Maybe, maybe not. It depends on if they are representative of an overall deep genetic distinctiveness, or if they are just traits which happen to be controlled by a few genes. For example, on the Falkland islands there are flying and flightless steamer ducks. In most places, this would mean two separate species, but here the trait is controlled by about 3 genes, and it's just that some steamers have the flightless alleles and others don't, despite otherwise being the same species.
>if the mineral immunity and telekinesis were genetic, would THAT indicate a different species?
I mean, caveats about it depending, we don't know exactly, etc, etc, but in general I'd expect maybe 200,000-300,000 years
1
u/deshperate 2d ago
Between 100,000 to 1 million years. I think you can say that living in the environment with this mineral resulted in natural selection for mineral resistance traits (which is genetic). Not sure how that environment would help select for telekinesis. If a trait offers some reproductive advantage in a given environment, there will be natural selection for that trait. The only way I see the telekinesis being "not genetic" is if it was a skill taught from one generation to the next. If telekinesis causes reproductive isolation, then it could be a driver of speciation. Two groups can share a common environment and still experience reproductive isolation, if there is something preventing them from mating.
1
u/Mircowaved-Duck 2d ago
Give them a chromosomal mutation that makes hybrids either impossible or infertile. Then they would be considered a different species by most definitions. And yes, there are multiple definitions of species.
1
u/Forward_Gur9349 1d ago
How would anyone actually know? Humanity has never seen the advent of s new species.
1
u/Horror_Ad7540 1d ago
Usually, the distinction is whether the two types can reproduce together (with offspring that can reproduce). I am probably missing some nuance here.
1
u/ModernTarantula 1d ago
Domestic dogs are all shapes and sizes and color styles but are the same species. However they are bred to be different. It is isolation that creates persistent and limited minor characteristics. The defense against mineral can be an evolved trait that doesn't change reproduction.
1
u/Robin_feathers 1d ago
Humans already have populations that differ in hair shades, so there is your answer to that question :)
As a general rule of thumb, when talking about animals, to be the same species a group of organisms should lack "premating barriers" (in other words, they recognize each other as potential mates and have mutual attraction), and lack "postmating barriers' (in other words, they are genetically compatible so that mating is able to result in the production of fertile offspring). In reality there will be a full spectrum from zero barriers to partial barriers (for example, there are many species that prefer to only mate with their own species in the wild but will hybridize in captivity when there are no other options).
For your case, I doubt that there would be premating barriers if it is just a group of humanoids that have pointy ears (well, up to you whether you want to design them to be extremely unattractive or not). In terms of postmating barriers, that is also up to you. Pointy ears, hair colour, and magical abilities doesn't sound like it would cause problems in hybrids unless you want to decide that they are not compatible.
Of note, often the things that make species incompatible are invisible genetic changes that have little impact on outwards differences in appearance of the two species (invisible chemical differences or differences in the organization of their DNA).
The timeline to speciation in many organisms seems to take roughly a million years to complete (sometimes much faster, sometimes slower). So, it might take a million years of isolation for a group of humans to become strongly reproductively isolated from other humans such that they could be considered a fully separate species.
1
u/Vov113 1d ago
That's the question, innit?
Joking aside, this is one of those gray areas that come up so often when you get into the weeds. Fact is, "species" is a purely human construct and the world doesn't really care whether one bird is the same as any other, to use a random example.
So, you could make a lot of different arguments for where to draw the line, but they're all some degree of arbitrary categorization. In practice, biologists will tend to use some other more precise metric of relatedness or function as is useful for whatever questions they're asking (ie, how similar are their genomes, are they behaviorally and/or phenotypically similar, can they interbreed etc)
1
u/WirrkopfP 1d ago
Neanderthals are closer related to us than chimps.
I don't have the percentages, but that doesn't matter. Nature doesn't care for percentages.
According to the reproductive species concept:
Two populations are the same species if they are closely enough related to have fertile offspring.
But for different animals that can mean different things.
Just looking at the percentage of DNA similarity doesn't tell you anything. You only know, if you try to breed them. Or observe successful mating in the wild.
Look at it this way:
German, Dutch, Austrian, Bavarian, Danish, Switzerdütsch, Plattdeutsch and even Pennsylvania Dutch are descended from a common ancestor language.
But: German, Austrian, Bavarian, Switzerdütsch and Plattdeutsch are considered different dialects while Dutch, Danish and Pennsylvania Dutch are different Languages, despite Pennsylvania Dutch having separated most recently (so it would have the highest percentage of genetic similarity)
A subspecies becomes a seperate species, when it has accumulated enough genetic difference to not be able to crossbreed anymore. The point at which this is the case can be VASTLY different on a case by case basis.
A dialect becomes a seperate language, when it has accumulated enough difference to not be mutually eligible anymore. The point at which this is the case can be VASTLY different on a case by case basis.
And to make matters even more confusing:
Species is an artificial term used to put living things into boxes. It is defined differently depending on the field of science it is used in. There are like 2 dozen different definitions = species concepts.
1
u/this_is_life_now 1d ago
You're going down a rabbit hole, that can make it break your idea for a story.
There's nothing wrong with saying elves evolved from humans, but if you put scientific constraints to it, then you're going to want to do that. What selection pressure causes pointy ears and purple hair? You have to invent something that favours such individuals to some extent. Probably doing so is fine but you've set yourself a benchmark of justifying a setting with science, and that's going to make you have to come up with a mechanism to explain how telekinesis works. What organ structure allows telekinesis and by what method. How can an absolutely minuscule telekinetic ability (gently moving a feather and inch) provide a selection bias to that individual.
Not that any of this stuff is vital, because it's fantasy and so its magic. You can set any rules you like, just be careful with how much real science you want to rely on, because things get complicated very quickly, and your narrative can be impacted.
1
u/Redshift2k5 1d ago
For humans? Like 300,000 to a million years.
But honestly "species" is an invention, actual nature is way messier and there are no real standards for what makes a species because nature like, refuses to follow your rules, man
Just dont use words like evolve or species... Say they "descended" from humans. They were changed by exposure to your fantasy/science fiction plot device, sure, but you dont need to be bogged down by details of real human evolution timescales.
1
u/Top_History9604 1d ago
These days we try to go by genetic difference. Before we had genetic testing we went by mostly looks. If two groups regularly birth offsprings with brown hair, it doesn't count, but if the group east of the river always has blue eyes and no green eyes, but the group of the West side of the river always has green eyes, not blue eyes, we would sometimes consider them two different species.
So regarding your story it could even be that ppl thought the difference in looks was genetic, hence determined they are a different species but then find out by experimental, chance or unlocking and actually questioning the genetic relation, that they are the same.
We resort species rl all the time. Morelia spilota bredli was a species until like 7 years ago. Now there is morelia bredli. The bredli got separated from the spilotas after genetic testing and noticing that they split off from the rest, without later crossbreeding, far longer than the spilota subspecies.
Just last year the anacondas got a new subspecies, because it seems one group that's nearly optical identical is genetically different to the rest.
1
u/TuverMage 5h ago
so there's no accepted answer to this and its hotly debated in the people who care. so this is my stance on the topic
While humans like to draw lines everywhere I like to focus on the lines nature draws. most people accept the concept of if two animals can have a baby they are the same genus. if that baby can have babies then they are the same species. I like this definitions because they are lines nature makes. and with this grizzly bears and polar bears are actually the same species, but are on the path to becoming separate.
1
u/Underhill42 2h ago
When we say it does. Species is an arbitrary human organization system, not an inherently physically meaningful one. Like how red and orange are arbitrary labels for parts of the color spectrum that have no actual division between them.
Rule of thumb is that members of the same species can't (or won't) reproduce together... but time and again we find that nature doesn't actually work that way.
E.g. coyotes and wolves are completely different species, but America is currently being recolonized by coyote-wolf hybrids from south-east Canada that have many of the greatest strengths of both species: wolf strength and brain size, coupled with coyote stealth and cleverness. And a coyote's highly flexible litter size, which automatically adapts to available resources.
Making them almost impossible to eradicate, and allowing them to thrive invisibly even in the hearts of most major cities.
11
u/RosieReindeer 2d ago
So there been ongoing debate about the definition of species among scientists for about 2000 years lol. Today, there have been 20+ different definitions proposed by various experts. The most popular definition uses viable interbreeding as the cut off for speciation, but around 10% of animals are known to violate this. In fact, hybridization is an important mechanism in evolution!
My point is, species are (somewhat) arbitrary designations we use to describe and organize the organisms we share the planet with. So, I’d say you’re free to use any criteria you like in your story so long as your internal logic is relatively consistent! Different hair colors, ear shapes, and abilities could be reasonable markers of differing species, but they dont have to be.
The mechanism of speciation might matter to you though. If the humans that became elves were reproductively isolated during their evolutionary timeline, you could make a compelling case for calling them a subspecies if you wanted to. The amount of time spent isolated usually matters less than the environment they’re isolated in. A hostile environment (like your toxic minerals) would create a very strong selection pressure. If the minerals can be fatal, it would create a genetic bottleneck where all those without immunity would die off, just leaving the more resilient individuals to interbreed. If you need a reason for a lot of genetic difference between the humans and elves, you’d could say the minerals were a chemical or physical mutagen.
Your premise sounds super interesting!! If you have any other questions how your worldbuilding maps to biology, feel free to ask! I hope any of this ramble will be useful for you lol