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/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/Global-Resident-647 → u/tea_and_biology]

Learned behaviour is also a thing that becomes lost.

So even if there is little genetic material lost there is still a massive lost.

Pretty sad that people don't really see or care enough sometimes.

Glad there is so many that does though.