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.
The 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.)
I'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.
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.
"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.
>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.
> 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.
> They are classified as a single species with the rest of humans because they can interbreed with other humans
This is not the standard for, e.g. birds, however. Consider the mallard. It's happy to breed (with fertile offspring) with just about any duck. However the ornithology community does not say "great, they're all ducks, maybe with separate subspecies". Instead they complain about "genetic pollution" wiping out species of ducks through genetic drift.
Myself, I think it would be perfectly reasonable to call these subspecies and keep the Biological Species Concept, but in actual usage the Biological Species concept is dead.
First, many organisms reproduce asexually and are thus classified into species on other grounds. Second, animals that have the ability to produce fertile offspring with each other are still often classified as separate species or at least subspecies (depending on whose definition you use) if they don't customarily interbreed and have differing appearances / characteristics.
> 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.
I'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.
Well obviously one or the other needs to go first. Why do you think the first one was chosen because it has the greater honor? If it was the other way round, wouldn't it look just as patriarchal to you ("Ladies first" and all that)? And are you sure they didn't flip a coin to see which parental gender would go first?
I don't know how they made the choice, of course. And if you have sexism on your mind, there isn't a right choice in this situation, I agree. However, if you take stock of all the similar choices (male or female) that we make in these mundane contexts, would it come out even? Or would it lean heavily to one side?
I 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.
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.
Just 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.
> 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.
The 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.
Some papers will use different definitions, and it can be confusing.
Between species (e.g. humans and chimps), it's most often considering "non-synonymous mutations," i.e. how many genetic differences there are in protein-coding genes (these are relevant to structure and function of the protein)
For distant relatives (e.g. humans and bananas), it's similar, looking specially at those genes which we can identify across many species (particularly those related to cell upkeep, DNA replication, structure, etc.).
For within-species, there are a few ways of doing it; you could model how much of the genome you expect came from each source (as this study did) (see admixture analysis, coalescence), and you could look for overall differences on the genome (of all existing variation in the species, how much is consistently different between populations) (see F-statistics for example)
> How are these numbers reconciled with other statements like 99% of the human genome is shared with Bonobos 
99% of any hominid genome - whether Neanderthal, Denisovan, or the "archaic" ancestor refererenced - is also shared with bonobos. The branching point with bonobos is at a much earlier stage of evolution, so all descendant branches have roughly the same affinity to them.
99% is comparing the entire genome, introns and exons. 92% is comparing known genes gathered from the human genome project and subsequent research. We don't know the exact genes expressed by our ancestors since RNA is far less likely to survive in enough different types of tissue to get a clear picture of the entire genome but 92% of the genes we recognize in ourselves can be found in early hominids using the latter's full genome sequence. Between epigenetics and embryology, we know that the whole intron/exon dichotomy is fatally flawed and evolutionary genetics has long turned to more complex methods to trace relationships, which are very nonlinear even in our near family tree.
Both numbers are ridiculous and meaningless so don't pay them any mind.
> Both numbers are ridiculous and meaningless so don't pay them any mind
I agree that they have little meaning for the purpose of individual and group identity. It's been pretty disheartening, for example, to see some people extrapolate from the discovery of Neanderthal DNA in non-African populations to the current economic disparities between non-African and African societies. Ironicallly, that is a reversal of the previous false stereotypes associated with Neanderthal influence in humans. I guess once it was proven, it had to be turned into a "good" thing.
But the percentages are meaningful for building a picture of ancient human evolution and migration.
Of course she was real. She had a mother, history and upbringing. Now as to whether the post-death Thrace ( "the second coming" ) was the "spirit/angel" of Thrace or an altogether different entity separate from Thrace ( like physical Gaius and the "spiritual/angelic/head" Gaius you see at the end of the series ) that's up for debate.
Her destiny ( teased throughout the series ) was to sacrifice herself to lead humanity to salvation ( earth ). It's similar to Christ in a way - self-sacrifice and the second coming to lead the faithful to the kingdom of god.
I've watched through BSG I think 3 times over the years, and I've come to the conclusion that I don't think she was strictly human, in the normal sense.
I think from day one of her existence, she was a kind of power on the same level as Baltar and Six's angelic alter egos. Watching it the first time when it originally aired, I had thought she was one of the Five (even though part of me thought that was too obvious, and a cop out)... and then the fifth member was revealed and it wasn't her.
Clearly the writers had given her a role beyond merely human or Cylon, something part of the grand scheme of God that Messenger/Head Baltar and Six were part of.
I love this theory. Not because I believe it, but because of how entrancingly bold it is. I sometimes wonder what we believe in that future generations will look down upon us for. Surely we haven’t discovered everything, right? Surely there are some things we think we know that is actually completely wrong.
Is it that human origins are rooted in chimp-pig hybridization? Probably not, but it is high on my “just might be crazy enough to be right” list. The odd similarity-dissimilarities among human, pig, and primate are just too interesting to be dismissed out of hand.
Exactly my point as well - science shouldn't shy away from stuff we wouldn't like. That's why I also respect Copernicus, Darwin, and Freud so much - they dared to tell us things we didn't like, but they didn't care much; they only cared about the scientific truth.
Human evolution is a field that's been evolving very fast lately. Even people who graduated only a few years ago are wildly out of date if they haven't kept up.
That said, classical multiregionalism is very, very dead and has been for awhile. Essentially what you're asking about has started to come up lately as a sort of in-Africa multiregionalism. This is a nightmare to model mathematically and so people just couldn't until recently when new fossils made it pretty hard to explain things any other way.
It hasn't fully emerged yet and many people don't really deal with it. Take for instance, this paper. One of the fundamental assumptions is that there was a singular set (or other time limited) of introgression events between archaic and human populations. That's a reasonable assumption in older models (and dramatically simplifies things), but it's possibly violated in an African multiregionalism model.
They claim it's not a problem because of symmetry, a point I'll admit I don't fully understand their explanation for in the supplementary material.
Nah, it had nothing to do with PC. Back then, PC was about labels: "disabled" (they tried to get "differently enabled" to stick!) vs. "handicapped," "little people" vs. "midgets" and stuff like that. You were even supposed to say "queer" instead of "gay," and some were just starting to use "gender" in non-grammatical contexts like referring to a person's "gender" (which was look-it-up-in-a-textbook incorrect back then).
Out of Africa feels less PC to me, but I won't pretend to understand the rationale behind what is and isn't considered PC a lot of the time. But I agree with GP: we have relatively few DNA samples and try to draw pretty big generalizations between them. Ituitively, I would expect patterns of migration in and out of Africa and all the continents to be far more complex than 1-time events from which entire populations then developed complete independently.
edit: On a related note, my siblings' DNA test results say that they're something like 4% Native American, yet we have very reliable documentation of pure British genealogy back on all lines almost all the way back to the 1500s. Very unlikely to actual have a modern link. I'm sure the companies are likely overplaying the similarity more than anthropologists would, but am I to conclude that I have a closer link to Native Americans than other random samples from Europe?
You can look at the data yourself, it's not hidden.
Also, the classical meanings of terminology like "negroid" or "caucasoid" doesn't really map to genetics. My personal experience is that they're almost exclusively used by people who aren't familiar with modern understandings of human evolution. There are a lot of cranks talking about it, so it's often best to avoid archaic terminology that might get you mistakenly grouped with them.
Absolutely not. There's no clear, ambiguous definition of "species" that does not have counter-intuitive implications. No, the classic "fertile over two generation" thing you learn in high school doesn't cut it. Also, the commonly used criterion vary from which domain is being dealt with.
In practice, this means that two individuals are said to belong to a different (resp. identical) species if everyone in the community agrees that they do. That's what it means to be a "social construct", not that the differences per se aren't real.
Justifying other statements on the lines of "X is a social construct" similarly, where X ranges across a variety of more-or-less controversial concepts, is left as an exercise to the reader.
#0000ff doesn't exist in nature. Human beings don't see color directly in hexadecimal values - indeed, additive color (RGB) as broadcast from a monitor and subtractive color as exists in nature are physically different processes. Rather, the perception of color is subjective and error prone (see a HN subthread on the color brown[0,1] or other examples of color illusions like the viral dress from a few years ago, or the red-grey illusion.
Blue is a social construct because what "blue" means is taught to us by the culture around us, and different cultures classify colors differently[3,4]. If one culture considers blue and green to be the same color, and another considers them distinct, that's not merely a disagreement over taxonomy, but concept.
"pure biology" is a human field of study, and is full of corner cases where different people disagree about the exact definition/distinction of individual species. I.e. many sub-fields have 2-3 standard reference books that do not 100% agree on which species exist, and where they do it often is "we've agreed to define it as this" (and then sometimes someone finds a new population inbetween or runs DNA tests and the whole debate kicks off again). Do you disagree with that, or do you merely object to calling that "social construct", and why?
Not mentioned in that Wikipedia article, but the explanation for "why is there no ancient plastic around" is that the civilization could have pre-dated oil. Not enough time may have passed for significant amounts of the stuff to accumulate in the planet, so the civilization would have never developed a use for it. It would have been a rarity to them, not a foundational cornerstone of civilization.
It's a cool thought experiment, but also very cool to think about how much we lucked out not just to be on Earth, but to be on Earth at this point in time. Emerge a bit earlier and suddenly industrialization becomes exponentially harder.
> The interbreeding outside Africa happened after our Homo sapiens ancestors expanded out of Africa into new environments.
Who's this "our"? Is the author implicitly excluding Africans from her audience (or whoever she's talking about), or do I have the timeline wrong and the aforementioned interbreeding ancestors went back to Africa, and then the "Out of Africa" expansion happened?
As a black person of African descent, I feel confident in saying that the group called homo sapiens, of which I and all of my ancestors for millennia am a part, expanded out of Africa into new environments.