7 ms·
How do we draw the line between species, exactly? Similar to this, you can distinguish between races and genders with skeletal tendencies now, but we're all one
by TallGuyShort 7y ago
How do we draw the line between species, exactly? Similar to this, you can distinguish between races and genders with skeletal tendencies now, but we're all one species. So when they are compatible enough to bone each other and said boning yields offspring, what exactly determines the line between 2 species and 2 distinct populations of 1 species?
edit: I'm also always intrigued by statements like this: "Interestingly, they suggest that 6%-7% of the genomes of West Africans is archaic in origin". I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees and don't even have the same number of chromosomes. So there's a lot more than that we have in common with some archaic species, and a lot less that we'd expect to have with closer relatives.
- solinent 7y agoI've looked into this, and there's no great way to do so, becuase the concept of species really just means large morphological changes. We assume everything is taxonomized (a tree), but in reality there is no tree--sometimes there is cross polination after some time apart. Ultimately they have a precise set of morphological criteria for each species, and they arrive at this criteria based on a sampling of animals and associating their morphology with their DNA. They also use string similarity algorithms to determine morphological order, so we don't strictly know the order at the most precise level. Of course, this is all very controversial, some people think we're always changing gradually and some people think we always change rapidly. I think they're both wrong--sometimes organisms change rapidly, and sometimes they change rapidly, depending on environmental factors. disclaimer: I'm no expert, I've just looked at it from an algorithmic view and read some taxonomical texts as I had the same question as you.
- moultano 7y agoThe further you zoom out, the more tree-like it gets, but if you zoom in on any particular node in the tree, like hominids, then it becomes a tangled mess.
- mirimir 7y agoExactly. It's my vague impression that you get species that can't interbreed after extended geographic/habitat isolation. But short of that, it's a tangled mess, with complex fertility patterns.
- solinent 7y agoI remember learning this vaguely as well, it's just a relatively useful rule with lots of exceptions, but it is not a law--it happens even after extended isolation: https://en.wikipedia.org/wiki/Hybrid_(biology) https://en.wikipedia.org/wiki/Hybrid_(biology) https://en.wikipedia.org/wiki/Interbreeding_between_archaic_and_modern_humans https://en.wikipedia.org/wiki/Interbreeding_between_archaic_... Some examples of hybrids without human influence (well that's arguable): https://en.wikipedia.org/wiki/Lonicera_fly https://en.wikipedia.org/wiki/Lonicera_fly https://en.wikipedia.org/wiki/Red_wolf https://en.wikipedia.org/wiki/Red_wolf The grand daddy of "hybrids" (twelve species): https://en.wikipedia.org/wiki/Celosia_argentea https://en.wikipedia.org/wiki/Celosia_argentea from here: https://en.wikipedia.org/wiki/Hybrid_(biology)#Speciation https://en.wikipedia.org/wiki/Hybrid_(biology)#Speciation Also you can go beyond hybrids: https://en.wikipedia.org/wiki/Polyploidy#Types https://en.wikipedia.org/wiki/Polyploidy#Types As an amateur I'd hypothesize if the species diverges and then relocates, but is subject to similar environmental pressure, the morphological changes won't be great enough to prevent the organisms from interfacing and then reproducing. We've determined this through string similarity algorithms, so really I'd say we can't be completely certain here either.
- mirimir 7y agoThanks! Lots of great links there.
- angstrom 7y agoI mean. Donkey+Horse = Mule, but the mule is sterile same with Tiger+Lion = Liger. I would assume they were closer relatives than that.
- tmn 7y agoA liger isn't sterile. It does have a lower chance of conception though
- yellowapple 7y agoTechnically a mule also has a lower chance of conception.
- fahadkhan 7y agoPedantic note: Female Tiger + Male Lion = Liger. Male Tiger + Female Lion = Tigon.
- dmos62 7y agoPedantic note: That's arbitrary patriarchism.
- im3w1l 7y agoThey will have different sex chromosomes (Y from tiger or lion) and different mtdna. So there might be some slight differences. And it's not out of the question that one is more viable than the other. EDIT: Wikipedia: "Notably, ligers typically grow larger than either parent species, unlike tigons"
- dmos62 7y agoI'm talking about naming; I'm not saying it doesn't matter which is male or female. Why is an offspring of lion and tiger called liger? Because the male was lion, and vice-versa for tigon. That's just plain patriarchism. Is it "bad"? I don't know. We certainly have a tradition for it. Edit: that's a lot of downvotes and no comments. Are we beyond talking about sexism, or is my tone so off-putting.
- droithomme 7y ago> when they are compatible enough to bone each other and said boning yields fertile offspring This was a definition of species for a long time. In recent years some have advocated for changing it a lot, to the point that they should just start calling different dog breeds their own species. Or to go the other way, are dogs and wolves different species? Is it homo neanderthalensis and homo sapiens or homo sapiens neanderthalensis and homo sapiens sapiens? In my opinion, Denisovans and Neanderthals are both obviously types of Homo Sapiens and the argument they aren't is at this point mostly promoted by those desperately clinging to the now disproven out of africa hypothesis.
- DFHippie 7y ago> the now disproven out of africa hypothesis. What? When was it disproven? There's evidence of interbreeding outside of Africa with other species, in some sense of that word, which also originated in Africa, right? Maybe I missed something.
- wnoise 7y agoThe strongest version of "Out of Africa" or "Recent African origin of modern humans" is "Modern man developed in Africa, and then spread throughout the world, essentially unchanged, completely eliminating other archaic hominids". Given known interbreeding with other hominids, this is clearly false, or at best incomplete to the point of being misleading. This is in contrast to a "Multiregional origin of modern humans", which still has "expanding from Africa" first, but far before modern man developed, followed by evolution and development everywhere without modern features coming from Africa "all at once". This too is clearly false and misleading. There were large migrations from Africa with large genetic distances from the native hominid populations, and the resulting mixture appears to be much closer to African than the native hominids. The modern synthesis is multiple waves of expansion out of Africa and significant gene flow making the tree look more like a river delta: lots of forking but also lots of merging, though not to the point of an undifferentiated sea either. The exact details are constantly being reevaluated as more genetic data is acquired. This is significantly different from the strong Out-of-Africa hypothesis, but claims there have weakened to include essentially this picture. The difference between the two point of views is a matter of scale at this point: how strong are the waves out of Africa, how much was displacement vs interbreeding, how much do genes flow in patterns besides out-from-Africa, how much is one giant expansion a reasonable approximation, etc.
- Zenst 7y agoAlas no hard and fast rule that I'm aware of that fits all cases. It's just a level of difference in which somebody goes, yip let's draw a line here and from anything going forwards is a new species. Heck, it certainly isn't defined by having interchangeable blood as we all know that don't work with humans.
- iguy 7y agoThe idea of discrete species is just a useful approximation to help us think about things. And it's an extremely useful first cut, imagine how confusing a farm would be if you didn't mentally keep chickens and bulls in different boxes. But when you look closely enough, there aren't really any such exact groupings in nature. Conception only involves the DNA of two individuals, not some larger group. And we know that species today have common ancestors, and it can't be that there was a precise second at which they became distinct, every split must have happened gradually. (Like us, animals also have their own heuristics about other animals, including what sort of things they will mate with, but it's imperfect. Denim jeans cannot reproduce with poodles, as it turns out.)
- Symmetry 7y ago"Essentially, all models are wrong, but some are useful." As to the 6% thing that's in the the same sense that you got 50% of your genes from your mother. Most of the genes there will be identical to the ones your father has on a codon by codon basis but their origin is your mother. And by looking at the 1% of genes where humans vary from each other we can tell which genes came from this ghost population.
- ppseafield 7y ago> So when they are compatible enough to bone each other and said boning yields offspring Apple trees mate readily with pear trees. Most citrus fruits are blends of other citrus fruits. Peppermint is a cross breed. [0] And then there's ring species [1], whose members can each mate with similar-enough-dna members and produce offspring. [0] https://en.wikipedia.org/wiki/Peppermint https://en.wikipedia.org/wiki/Peppermint [1] https://en.wikipedia.org/wiki/Ring_species https://en.wikipedia.org/wiki/Ring_species
- ummonk 7y ago>How do we draw the line between species, exactly? Similar to this, you can distinguish between races and genders with skeletal tendencies now, but we're all one species. So when they are compatible enough to bone each other and said boning yields offspring, what exactly determines the line between 2 species and 2 distinct populations of 1 species? You can't. In practice, extinct branches of humans are classified as separate species, and animals are classified as a bunch of species because biologists get credit for discovering new species. In contrast, living branches of humans (e.g. bushmen vs. pygmies vs. everyone else) ar classified as a single species even if they have evolved largely in isolation for hundreds of thousands of years and rarely interbreed, because classifying them separately could give ammo to racists and worse. >I'm also always intrigued by statements like this: "Interestingly, they suggest that 6%-7% of the genomes of West Africans is archaic in origin". I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees and don't even have the same number of chromosomes. So there's a lot more than that we have in common with some archaic species, and a lot less that we'd expect to have with closer relatives. It usually means 6-7% of genes that vary between humans.
- danans 7y ago> In practice, extinct branches of humans are classified as separate species They were classified that way, until the presence of Neanderthal & Denisovan DNA was discovered in modern humans. > In contrast, living branches of humans (e.g. bushmen vs. pygmies vs. everyone else) ar classified as a single species even if they have evolved largely in isolation for hundreds of thousands of years and rarely interbreed They are classified as a single species with the rest of humans because they can interbreed with other humans, not for political reasons. We couldn't draw the same conclusion about extinct branches until recently because we don't have living groups of them that we can observe interbreeding. Now that we see the genetic evidence of that the classification has changed.
- xeeeeeeeeeeenu 7y ago>They are classified as a single species with the rest of humans because they can interbreed with other humans https://en.wikipedia.org/wiki/List_of_genetic_hybrids https://en.wikipedia.org/wiki/List_of_genetic_hybrids
- brailsafe 7y agoJust because you can define a group, doesn't mean that's inherently divisive. Like you mentioned, species are approximately defined by their ability to mate and produce offspring, as part of a larger taxonomical hierarchy but certainly not exhaustive on its own.
- danans 7y ago> I know it's over-simplifying for the lay-person, but 6-7% is the high end of what people claim is the genetic difference between us and chimpanzees, and we can't even reproduce with chimpanzees Those percentages aren't measuring the same thing. Chimp to human is a total genome comparison. Human to Hominid ancestor X is based on identified humane genes. The latter is a tiny subset of the former.
- DoreenMichele 7y agoHow do we draw the line between species, exactly? As others here have noted, it's generally or historically been deemed to be a pairing expected to produce a fertile offspring that can interbreed with others of the same group. Though, really, DNA is just two RNA. We are made up of the same code that makes bacteria and even viruses. So it's bound to be messy and highly hackable. https://www.iflscience.com/health-and-medicine/ancient-viruses-are-hiding-within-your-dna/ https://www.iflscience.com/health-and-medicine/ancient-virus... I can't readily find a really good article about the (controversial) theory that humans descended from a pig-chimp mating, but you can Google it.
- lowdose 7y agoI found an article written in 2013 and it was an interesting read. But it seems the author was not aware that domestication also leads to a change in physical appearances in every animal we know thus maybe cause and effect are reversed? In a recent episode of the Grand Tour locals from Colombia were proud to fuck their donkey so I didn't want to dismiss this hypothesis on forehand. https://www.google.com/amp/s/www.dailymail.co.uk/sciencetech/article-2515969/amp/Humans-evolved-female-chimpanzee-mated-pig-Extraordinary-claim-American-geneticist.html https://www.google.com/amp/s/www.dailymail.co.uk/sciencetech...
- tylerjwilk00 7y agoThere are not sharp lines, just fuzzy boundaries. We do have to discuss and reason about living creatures with other humans though, so it's helpful to name and categorize, just know that the names and categories are a human language construct, nothing more.
- fredgrott 7y agoJay Gould and the Ant Ecologist have the best info on that.Eo Wilson his college book for ecology classes.