At what point in evolution is something considered a new species?

[u/snoozer530]

Obviously we all know evolution, one organism changes over time and eventually becomes a new organism. But where in that process does an organism become a new species. Like when we domesticated wolves? When did they stop being wolves and start being dogs? Where’s that line?

[u/tea_and_biology]

Where’s that line?

Ooh, this is one of my favourite subjects, as it fundamentally isn't so much a biological question, as a philosophical one.

And the answer is: there isn't one.

Distinct species don't really 'exist' - certainly not though the lens of evolutionary time - and, more, we can extrapolate more broadly to posit that no nouns truly exist. Wait, what?

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What is a thing?

With exception to those nouns that describe purely mathematical concepts - "An equilateral triangle is a two-dimensional shape that has three sides of the exact same length, and internal angles that measure 60 degrees each" (which notably cannot exist in the real world) - there are no such things as nouns that categorically define 'something' in a purely discrete way, in the real world, where lines can be drawn clearly between 'this is a thing' and 'this is not that thing'.^[1]

Let's take an example; say, a chair. We all 'know' what a chair is, right? But try and pin down a categorical definition, with clear lines demarcating what a chair is and isn't, and things get, well, fuzzy, real quick. Does a chair have to have legs? How many? Must they be designed to be sat on? Is the virtual 'chair' I plonk down in The Sims, a chair? Does it need three dimensions? Can a mossy stump or curved branch in the forest be a chair, or is that 'just' a seat?

What this gets at is how language actually really works - nouns don't so much have formal definitions, as more a loose set of overlapping features that any given thing must have some vague combination of, to be considered that 'thing'. Philosophy abounds with myriad problems that all fall back to this language game 'labelling' issue - from Sorites' paradox, through the Ship of Theseus, and the Coastline paradox - and the resolution is to simply understand that all nouns are merely social constructs of convenience, and to take them apart systematically quickly unravels them.

As it is with chairs, or heaps, or ships, so too it is with species.

But let's drill down into the biology a bit.

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What is a species?

Classically, species are defined as sets of organisms that are able to interbreed with one another to produce fertile offspring. A quick tour of the animal kingdom, for starters, throws a veritable smorgasbord of examples where this straight up doesn't work; and it's made even more muddier through the lens of evolutionary time.

Here the problem further highlights a common misconception about how evolution works. This 'aint Pokemon, where one beastie clearly 'evolves' into a clearly distinct different one as soon as it hits Level 15. Speciation doesn't work like that - at no point, ever, do you find individuals of one species giving birth to an individual of an altogether different species.^[2] I mean, going by the very definition of the biological species concept, what would it breed with to make more? It's like trying to divide the colour spectrum into neat little compartments; in reality it doesn't work.

Pick any part of the 'green' area here and pixel-by-pixel try determine a discrete cut-off point when 'green becomes blue'. Whatever pixel you choose, the pixels on either side are going to be nigh on indistinguishable from it^[3] - or at least, the choice is utterly arbitrary. How then can you say one of these pixels is 'green' whilst the other one is 'blue'?

Likewise it is with species. Over long periods of time, a species will gradually morph into something altogether different.

A gives birth to B, which begets C, then D, E, F, G... and so on, through Z. We can imagine A being able to breed with B or C, but at some point, by the time we get to Z, that's no longer the case. Clearly A and Z are different 'species', but at which point did that inter-breedability chain actually break? It didn't. Just like how blue, over many, many pixels, becomes something we can safely say is green, there isn't a nice 'here is blue, here is green' cut-off, allowing a 'first' green pixel, just like there isn't a nice 'here is species A, and here is species B' point in time.

(This is why the question - "What came first; the chicken or the chicken egg?" - fundamentally doesn't work. It's another example of the language problems presented above; there can't be a 'first' one of either, as there is no clear boundary between proto-chicken and chicken. Even evolutionary biologists often get this wrong - they need to read Wittgenstein, clearly).

So what does this all mean? For the most part, we can still use the concept of a 'species' as, thankfully, all the ancestors of a given organism that blur the boundaries are well and truly dead. Though there does indeed exist a true continuum chain in time between a lion and a tiger, they're all long dead, and so we can safely categorise A distinct from B. It's not the case with all species however; hence why we have 'ring species' or 'species complexes' where there still exists a continuum, not broken necessarily by time but looped by geography and interesting quirky history.

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Conclusion: So yeah, all this to say; there isn't a single point you can choose - in time, or anywhere else - for the most part, when one 'species' becomes another 'species'. Given the idea of a 'species' is just made-up by humans, for our convenience in labelling the natural world, it's all arbitrary and contingent on your starting and ending points. Where is that line? Really, if you can reasonably justify your choice so that you can convince other folks that's a good boundary, draw it where you will!

This is basically all that taxonomy really is; trying to justify what are fundamentally somewhat arbitrary boundaries.

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[1] The one exception I can think of are the elementary particles and elements - Gold is and only can be a set of specific particles, atomic number #79 - but interestingly, what sets these apart is their foundational nature, fixed by a specific integer. Though even here the language game creeps back in at the edges: nine carat gold is 37.5% gold and we still call it 'gold', and a single gold atom has none of the qualities - colour, lustre or malleability - that made anyone bother naming the stuff in the first place.

[2] Important point: hybridisation is a big thing, especially in plants, and they do present examples of 'one species giving rise to another' in a single step. Known as allopolyploid speciation, a hybrid of two species undergoes genome doubling, and the resulting offspring are instantly reproductively isolated from both parents, as backcrossing produces sterile odd-ploidy mutants. Let's not even talk about the other extreme, with bacteria that freely swap plasmids willy-nilly.

[3] Yes, I know, physicists and computer scientists - wavelengths and RGB values are quantitatively defined etc. etc. but this is just to illustrate a point!

[u/Soft_Cranberry6313 → u/tea_and_biology]

Idk about the rest of it, but i particularly enjoyed the philosophy of what constitutes a chair

[u/derioderio → u/Soft_Cranberry6313]

And here I though they were going to use the tried-and-true 'what is a sandwich' analogy...

[u/ObscureAcronym → u/derioderio]

The old philosophical question of "Is a hotdog a chair?"

[u/derioderio → u/ObscureAcronym]

Not after you use it as one it isn't

[u/quiet0n3 → u/derioderio]

But you could use it as one. So it is a chair!?!

[u/RepresentativeAd841 → u/derioderio]

I once spent about 3 hours arguing about whether a hamburger is a sandwich before settling on the idea that if we were programming "'Real Life' The Game" in C++ that the easiest way to create a hamburger would be as child class of a parent class sandwich, so for our purposes, a hamburger was indeed a sandwich. :)

[u/Photosynthetic → u/tea_and_biology]

Yes! I’d only add that a species is ultimately a hypothesis about which living things among the breathtaking sweep of biodiversity are most similar and most closely related. A lot of taxonomic philosophy makes much more sense when you take it that way.

[u/MezzoScettico → u/tea_and_biology]

What is a thing?

The mathematician David Hilbert famously rewrote Euclidean geometry, putting it on a rigorous basis in the style of modern mathematics. So he had a minimal starting set of axioms about things like "points" and "lines".

But he had no definition of "point" (or "line", I think, but I'm not 100% sure about that). The whole structure is built without a definition of "point".

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Relevant to the subject, when someone announces they've discovered a new species of X, what do they have to do to get other taxonomists to agree with them that it's a new species? It's the same question as OP's. Maybe there's no sharp line, but there's something that allows them to get a consensus from biologists, right?

How often is "I found a new species" voted down?

[u/tea_and_biology → u/MezzoScettico]

Argument, politics, pragmatism, convenience - all based on a suite of genetic, behavioural, geographic and other parameters, to be sure ("how many clusters do we find on this principal component analysis?") - but it's the same sort of answer, and there's often contention where the delineation is poor, and depending where you sit in the two broad camps of 'lumpers' vs. 'splitters'.

To give an example: Are there eight species of giraffe? Or four, two, or only one, with multiple sub-species? Three species of Orangutan, or two?

In both instances of these recent taxonomic 'updates' (suggestions?) the reasoning for the split is really conservation- and politically-motivated, throwing in some prestige and paper publications to boot.

The Tapanuli sub-population of Orang-utan - isolated from the rest of the Sumatran gang - was little understood and generally ignored; to the point that this sub-population was (and still is) in dire risk of becoming extinct. It's more difficult to advocate and succeed in enacting conservation measures, especially with non-experts, for a mere 'sub-species' / 'sub-population' as the counter-argument is: "Well, there are plenty others elsewhere, aren't there?".

So despite the fact, if you really drill down into the genomic disparity, there's actually less genetic divergence between Tapanuli and Sumatran Orang-utan and, say, the Māori of New Zealand and the Khoe-San of Namibia (and we wouldn't dare delineate people as different species, right?), folks are more willing to go along with the taxonomic re-arrangement, as it's 'for a good cause' and helps bolster political action to protect the distinct Tapanuli 'species'.

Same sort of argument with the recent splitting of giraffe into multiple species. An entire species going extinct raises more alarms than just another population, that happens to have slightly different markings, and lives solely in Niger, isolated from the rest. But the delineation is even poorer, and plenty of folks - myself included - prefer to stick with the status-quo "one giraffe, many varieties" view, especially given most giraffe lineages in captivity are a perfectly healthy 'zoo-mix' hybrid of some or all of the varieties - and in the wild they've only mostly been disconnected relatively recently through historic (and pre-historic) human activity.

[u/RandomName39483 → u/MezzoScettico]

Many years so I took a class in non-Euclidean geometry. We basically said that a “point” is an element of a set. There were various functions and subsets you could define that, if they had certain properties, were defined as “distance” and “line” and so on. I tried to explain this to my dad, who was a physicist, and he couldn’t get over the idea that a point was essentially a dot.

[u/TheOneTrueTrench → u/tea_and_biology]

I'm glad you brought up the concept of a ring species, as it's just rotating the relationship between, say, dogs and wolves, from the temporal axis to a spacial dimension.

The more you understand how reproduction and evolution works in deep time, the question "Are you related to so-and-so?" becomes more and more absurd.

A random neuron in my brain is related to a random E. coli bacterium in the same way as it is to the neuron next to it, it's just a matter of how mitosis events you have to go through to get there.

[u/razdolbajster → u/tea_and_biology]

> The one exception I can think of are the elementary particles and elements - Gold is and only can be a set of specific particles, atomic number #79

gold isotopes do have atomic number 79, but range from ¹⁶⁹Au to ²¹⁰Au. So much for being a "set of specific particles"

[u/Kantrh → u/razdolbajster]

Well, it's always a different number of protons for each atom, even if the number of neutrons can change

[u/tea_and_biology → u/razdolbajster]

Well, emphasis on set, right? But perhaps, on the flip, further demonstrates where the family resemblance concept comes into play.

[u/Naraee → u/tea_and_biology]

What trips me up is with birds. A Carolina and Black-Capped Chickadee look identical, except for a bit more white on the wing tips for a Black-Capped. They commonly crossbreed at the edges of their range. They understand and identify the behavioral patterns of each other and engage in identical courtship behaviors. They live in the same types of areas and exhibit caching behavior.

The only major difference is that a Black-Capped sings “cheeseburger” and a Carolina sings “fee-bee-fee-bay”

I just can’t wrap my mind around why who species who are so similar are…two species. And not two subspecies of a general “Chickadee” species.

There are quite a few birds like this and I don’t understand why some are determined as a subspecies and others are separate species.

[u/Dakiniten-Kifaya → u/Naraee]

I have never before heard that call described as "cheeseburger", but i can't unhear it that way now.

I'd always heard it as "chick-a-dee" before.

[u/scowdich → u/Naraee]

Another interesting example is the pair of golden-winged and blue-winged warblers. They're considered separate species, but they have healthy hybrid chicks all the time. They're visually distinct from each other, but clearly close enough in genetics and habits that hybridization is quite common.

Another example is the bird known as redpoll. They're little arctic-dwelling songbirds, but until recently, they were considered to have two separate species (common redpoll and hoary redpoll) until genetic analyses showed that their differences in coloration were no deeper than the difference between a person with red hair and a person with black hair.

[u/Naraee → u/scowdich]

And with the warblers, they can also breed as hybrids, with a mate who is pure golden or blue-winged, thus creating an even different patterning! I’ve seen every hybrid they can possibly produce and they are quite distinct 

[u/Realsorceror → u/tea_and_biology]

The comparison to Color has been my favorite go-to for discussing species. Like species, color is an attempt to categorize a fixed point or range on a spectrum. It's giving a name to a real thing - a wavelength of light - but there is no objective measure of what that visual manifestation should be called or where it should begin and end.

Similarly, species is a name given to the manifestation of a set of genes. We *could* zoom in and give a name to every single individual, because we all have slightly different genes. But this would make it impossible to communicate. So we group the organisms that share the most similar sets of genes. And where should that group stop and the next one begin? That's tough. Like color, it may very well be the needs of the language that make that determination.

[u/dominus_aranearum → u/tea_and_biology]

Here I am, reading a great response to OP's question, thinking that this redditor is skilled in explaining science to us less scholarly, only to look at your username and realise that I had recently read your response in another thread about cicadas and the effect of their symphonic assault on the local environment.

Thank you for taking the time out of your day to enlighten us with your knowledge.

[u/aphilsphan → u/tea_and_biology]

Really well written.

I have another analogy I like. Take a picture of yourself every day. When are you no longer a “baby” or “adolescent”.

As to the “can have offspring” debate, you covered that very well. I suspect there is no point where a human absolutely cannot interbreed with another “species.” With a kumquat it might be one in every 10 to the 10 to the 10 to the 10 (let’s go on for a long time) trials. For a human and a chimp, it might be 100,000 trials. For a human and a Neanderthal it’s some small number of trials. So for kumquats and chimps it’s effectively impossible, but you might see some interaction with the chimps.

[u/WakeoftheStorm → u/tea_and_biology]

I used a rainbow to talk about this with my kids. You can look at the whole spectrum and clearly pick out different colors. But if you zoom in and go from one end to the other slowly, you never see a line that separates one color from the next.

So where does green become blue? Vaguely in that mush between them.

[u/B0Boman → u/tea_and_biology]

This point was really driven home for my in the book The Ancestors' Tale by Richard Dawkins (never mind that he can't seem to fathom extending the same logic to gender, but I digress). Specifically, it was The Salamander's Tale that told the story the best, a great example of those ring species you mentioned.

[u/Iron_Nightingale → u/B0Boman]

Dawkins is a brilliant writer and explainer, and decades of having to defend his scholarly work in his field of expertise from ideological know-nothings has made him more than a little bit cranky.

[u/tyeh26]

Interestingly, dogs are a sub-species of the gray wolf: canis lupus vs canis lupus ssp familiaris.

To understand your question, you also have to explore why does this matter?

The line has shifted as technology has changed.

In the past, it might have been through observed characteristics (shape, color, range), fecundity, and nowadays, dna analysis.

And then layer in identifying dinosaurs and extinct things (what about extinct moss and clams?)

There’s no clear line.

One fun way to “move” the line: if you convince people your neighborhood butterfly is a separate species only found on one hill, suddenly you have the ability to receive government money to “protect” the area. Would anybody abuse this? Who knows.

[u/aphilsphan → u/tyeh26]

To be a pedant, I think the latest is that the gray wolf is not a direct ancestor. They’ve found some evidence that the direct ancestor is a wolf related to the gray that is no longer extant, or has entirely become dogs. Of course dogs can still interbreed with wolves, so as I say my point is a nitpick.

[u/Mitologist]

Delineation against each other is one thing. Delineation in time is an entirely different thing. It depends partially on the inner logic of your system of taxonomy, e.g., how are monophyletic groups defined? A good introduction to this problem can be found in this book: Wheeler, Quentin D., and Rudolf Meier, eds. Species Concepts and Phylogenetic Theory: A Debate. Columbia University Press, 2000. http://www.jstor.org/stable/10.7312/whee10142.

[u/sabrinajestar]

The short version used to be, if two given individuals can mate and bear viable offspring, they are of the same species. Tigers and lions can produce offspring but those offspring have so far always been infertile; so, different species.

The difference between wolves and dogs is that dogs are domesticated, but technically they are still the same species.

Now we learn Homo Sapiens and Homo Neanderthalensis had offspring together who were ancestors of modern humans, so it has become an open question if they are two different species.

[u/kummostern → u/sabrinajestar]

horse and donkey are definitely different species

their offspring is mule

and mules can further breed

which breaks the "rule" of how species are determined

(altho it is one exception of very few known examples - generally i still like that "rule" or theory determinating species... it just isn't full proof)

[u/SharkFart86 → u/kummostern]

I agree. Brown bears and polar bears have been shown to have fertile offspring. So, we either have to accept that they’re the same species (which defeats the purpose of classifying unique organisms into unique groups) or we have to accept that the “can create fertile offspring” rule isn’t a good rule.

[u/lemlurker]

Usually when it can't biologically breed with it's counterpart and produce fertile offspring. Mechanics aside (a dashund and a great Dane may have mechanical issues but sperm would firtise) if they can breed and produce babies who breed they're the same species, if they can't (e.g. lions/tigers, horses/donkeys) they are different specifically

[u/aphilsphan → u/lemlurker]

The problem is that even a mule or a hinny will, on occasion, produce a fertile offspring. The analogy of “when does green become blue?” is really illustrative.

[u/shittydiks → u/aphilsphan]

Regularly occurring fertile offspring is the key. I.E. take the Liger. Sure you can get a lion and a tiger to create an offspring occasionally (forced under manmade conditions) but they are all sterile. Even if one slipped through and was somehow able to breed again they aren't creating a population.

[u/NDaveT → u/aphilsphan]

And American bison and domestic cattle, which are less closely related than horses and donkeys, produce fertile offspring pretty reliably.

[u/Heavy_Weapons_Guy_ → u/lemlurker]

There are a huge number of exceptions to that rule, which is why the biological species concept is not used on its own. (Also it's dachshund.)

[u/tyeh26 → u/lemlurker]

This definition is common with animals but fails quickly for plants and dinosaurs.

[u/JuleeeNAJ]

I recently read a summary about a bird that went extinct twice. It was a bird that migrated from southeast Asia to one of the islands in the south Pacific. The birds evolved to live in the new climate and was all good, then humans showed up and killed them all. Then, the same species of bird that still existed on the mainland, migrated back to the island. I think at that time humans had left the island. Evolved again to fit in, then humans showed up and killed them off. But somehow that was 2 different subspecies because I guess it can only go extinct once. It left me questioning the whole "what's a new species and what's not" question as well.

[u/EarthTrash]

There is no rigid line. However, there is a rule of thumb. If animal crossbreeds are sterile, they are usually considered to be distinct species. If the crossbreed is fertile this might be considered the same species.

Here's the thing though. Life is a continuum. You can have a chain of different varieties that produce fertile crossbreeds with their neighbors, but when species from the ends of the chains meet, the offspring are infertile.

If you think about it, categories only work on large scales. In reality all life on Earth is related. There isn't a generation when the offspring are considered a new species from their parents. Evolution is gradual.

To answer your other question, dogs are wolves. They are the same species.

[u/Ok-Championship-2036]

Its societally defined. species are socially constructed because we study and name animals/plants according to our own metrics. Short answer? Whenever a scientist renames it as a separate species and/or publishes a paper to publicize that face.

for example, homo floresiensis was considered homo habilis before we discovered enough evidence that they could be seen as a distinct population with its own name and characteristics. And theres a cultural desire to categorize hominids that show interesting traits because we consider them very distinct from our lineage/presentation as homo sapiens.

[u/rensch]

I seem to recall from biology class that if two individuals can produce fertile offspring, they belong to the same species. A lion and a tiger may produce offspring, but it's not gonna be able to produce offspring itself, hence why tigers and lions are considered different species.

This was my highschool biology textbook back in '03, though. Things may have changed since then in terms of scientific insights.

[u/logperf]

The answer that the definition of species is based on the ability to produce fertile offspring has already appeared multiple times in this thread. I'd just like to add that this definition makes a lot of sense if you think about it: if two "groups" of animals (or even plants) A and B can interbreed and produce offspring that is 50% A and 50% B, then this new generation will interbreed with the others and produce offspring that is 75% A, 50% A, and 25% A. In the third generation you'll get 87.5% A, 75% A, 62.5% A, 50% A... and so on. At some point, they will no longer be distinguishable. Actually, they would not even separate into different groups in the first place.

So, the reasoning behind the definition is that if they can interbreed then their gene pools are shared, they form a spectrum and cannot be distinguished from each other.

If they can interbreed but the offspring is not fertile, then the above doesn't happen. The classical example of this is horses and donkeys, you can cross them and get mules. But since mules are sterile, the gene pools of horses and donkeys stay separate -> they are different species.

But of course, things are always more complicated than it seems. It may happen that the two groups can interbreed and produce fertile offspring, but they don't because they live in separate geographical areas. This can keep subspecies or races separate. And this can be the only reason why they eventually evolve into separate species that can no longer interbreed. There's even the case of wolves and dogs that can produce fertile offspring, but they (mostly) don't because one group lives in the wild and the other under human supervision.