It's interesting to note that the fossil record shows an apparent overall reduction in the morphological variety and number of hominans in the million years or so before present.
When we talk about Homo ergaster and Homo erectus it doesn't do justice to the significant variation among, and geographic distribution of, the fossils that are grouped under these species names. It's hard to know which variation can be accurately attributed to intra-species variation or sub-species or even separate species.
However, what is clear is that there is a great deal of variation in Africa, Asia, and Europe around the time of the "eretines". My feeling (back when I was a student) was that the archaeological evidence suggested an ongoing adaptive radiation of sorts, rather than the classic picture of a steady and relatively homoegeneous trajectory towards modern humans. But a lot of new research has been done since then that I'm not up to speed on.
Prior to the displacement and extinction of the remaining human forms there was already a reduction in the number and variation of Homo species. Even within our own species, there was much greater variation some 200-150kya.
There aren't any easy (accurate) answers to these sorts of questions, which is also why they are such fascinating areas of research. Understanding all the factors and events involved is very difficult with the type of information available.
You just have to look at the incredible lack of hominid (great ape) fossils for the last many million years of years to see know how difficult it can be to piece together an evolutionary history of a taxonomic group.
As far as I know, the adaptive radiation theory is now held as correct for hominids just as it is for every other group of species. The "classical" teleological viewpoint doesn't hold up to scrutiny for the reasons you cited.
Not every period of evolution in a taxonomic branch is going to involve adaptive radiations. Although early human evolution is generally thought to have involved an adaptive radiation, by the time we get to 2mya a lot of the literature was assuming only 2-4 species existed over the next 2 million years.
Teleology was used somewhat tongue-in-cheek. The older literature was problematic because it aligned too neatly with anthropocentric ideas of goal-oriented evolution, and gave rise to nonsense objections like "Where is the missing link?" and "Why are apes still around?"
I don't doubt the integrity of the scientists who were involved with the earlier literature, but in hindsight it looks an awful lot like a teleological bias.
There aren't any easy (accurate) answers to these sorts of questions, which is also why they are such fascinating areas of research. Understanding all the factors and events involved is very difficult with the type of information available.
Speciation is only something that can be determined after the fact, anyhow. Species are entities we use to discuss the combination of innumerable bits of historical happenstance. Our being the only human species left might be due to little more than luck.
Contingency could well be involved. But it's not particularly easy to decide what constitutes a separate species, even with extant organisms. The categorisation of fossils into separate species is probably not as interesting or important as trying to understand what can be deduced from the amount of variation between and within populations.
Well, maybe incredible isn't the best word. There are so few of them and it makes piecing together the evolution of modern Great Apes (particular over the last 10 million years) particularly difficult [1]. Perhaps their habitat was not conducive to fossilisation of remains. Don't really know enough about that area of research. But I'd guess that preservation bias is a factor.
Ecologist here. Look into "competitive exclusion" (http://en.wikipedia.org/wiki/Competitive_exclusion). Basically two species that compete for exactly the same niche cannot coexist: the species with a higher fitness will win out, causing the other to become extinct. Stochasticity plays a role as well in determining who stays and who goes. And, as the environment and community structure changes, the definition of fitness changes as well. There is a large body of experimental research on this topic.
Throughout history there have been other hominid species and the amount of time that more than one species have coexisted has been relatively small because one species invariably drives the other(s) to extinction.
The difficulty I have with this explanation is that the Earth is a big niche that we've come to dominate.
At every point the sapiens sapiens migratated to a new area already populated by a previous human group (a previous wave of migration from Africa) the sapiens sapiens would have to be dominant in that niche - even though we know the Earth is extremely varied.
A different explanation is that we were the only hominid group that survived a dramatic climate change (change out of Ice Age, or volcanic change etc) and our 'niche' was the ability to adapt to a radically changed environment in all parts of the planet that we inhabited.
I'm not an ecologist, though, so I might be missing something.
Also, "relatively small" may have been up to 10,000 years, for Neanderthal and sapiens in Europe. I know this is relatively small on evolutionary time, but its less than an order of magnitude from the amount of time that we've inhabited many places on earth, suggesting that it might have been possible for other human species to survive to modern times (ie if the land bridge between America and Asia hadn't formed until just a little bit later).
I think they went extinct because we were horrified by them. Horror movies are most terrible when the creatures there are mostly human, but somehow different. Humans don't like different kinds of humans.
If a human being sees another human that is different enough to fall into the horror movie monster category, we immediately kill it. I think that humans would have this reaction to the other human species, otherwise why are our horror movies dominated by humanoids, and not by animals?
Other animals that have such horror reactions are snakes, rats, cockroaches and spiders which are also horror movie material. Of all the bad stuff in the horror movies, the only one that is not directly around right now is the strange looking humanoid.
> I think that humans would have this reaction to the other human species, otherwise why are our horror movies dominated by humanoids, and not by animals?
For the same reason that Dr. Who/Star Trek aliens (not all intended to be horrific) are humanoid - they are played by humans in a costume.
If we killed off other humanlike species because they terrified us, wouldn't we have also killed off other species that terrify us, like snakes, rats, cockroaches and spiders?
I can't find a reference right now but I remember reading somewhere that European Homo Sapiens contain genetic evidence of interbreeding with Neanderthals, and Asian Homo Sapiens contain genetic evidence of a second, later round of more interbreeding with Neanderthals. I think that suggests we didn't find them all that horrifying :)
Snakes, rats, cockroaches and spiders are very difficult to kill off. If we could, we would wipe them off, but even with modern technology, we can't get rid of them, back in the past it would not have been possible.
The reference to interbreeding with neanderthals is a single DNA study, and it does not say what you think it says. It says that non-african humans share a more DNA with neanderthals than africans. The shared DNA could have come from the exit point from Africa or some other location where everyone leaving Africa passed through (like the horn of Africa). The neanderthal breeding theory is not credible at all, because the strongest overlap between neanderthals and modern humans on a DNA basis comes from the far east, where there is no skeletal history of neanderthals existing.
Might as well kill all the flowers and plants too and just make food directly from organic chemicals in processes powered by solar panels and cut living organisms out of the equation completely.
Not quite -- we simply drew down the population of Anopheles enough that malaria was unable to spread. DDT is a very effective insecticide, but resistance has been described and can spread if it is overused; in fact it is estimated that agricultural use of DDT causes more deaths from malaria by contributing to DDT resistance in Anopheles and thereby affecting vector control operations.
All of those other species you mentioned can hide from us easily, can reproduce relatively quickly, and/or can live in environments that humans can't survive in. Not so with humanoids.
Evolutionarily, that would make sense as well: creatures similar to us are likely to be competing for the same resources -- and as they are different they can't be trusted to collaborate.
If I had met another hominid on my way, I doubt I would want to kill it right away because it horrifies me. I would rather expect the natural trigger that prevents me from killing other people to turn on.
I'm not saying that different species of hominids didn't kill each other, I just think that the main reason behind killings was fight for food and other resources, not the low level fear instinct that we experience during encounters with spiders, snakes and worms.
Your applying your modern-day, urban culture to ancient tribal societies. Studies of our remaining modern day tribal societies in Papua New Guinea disagree with you. I suggest reading "Guns, Germs, & Steel"
I makes me wonder how many mythical humanoids are remnants of our collective memory of these other humans: giants, dwarves, elves, trolls. Could troglodytes be Neanderthals?
Similarly Dragons could be the result of ancient man finding dinosaur bones and extrapolating what the creature must look like (a creature with bones made of stone could surely breath fire).
There's also various disorders that produce dwarfism and giantism and other forms that might have looked like mythical creatures before medical science knew about these things.
What amount of genetic variance between two groups of humans would account for / trigger a classification of a different species?
That is, is there a quantifiable amount of variance between say, a fruit fly and a different kind of fly, beyond which it is apparent they are two different species? Something like "2% of genetic variance, therefore a new species"?
Any sort of search on Google only turns up racist sites - apparently "genetic distance" is a codeword for rather unfriendly attitudes towards blacks - obviously I don't know the right technical terms to look for.
Species are an attempt to label a continuous phenomenon with discontinuous labels. Sometimes the cutoff point is the ability to produce fertile offspring, but that doesn't work all the time. It's always going to be very subjective.
Well put. I kept thinking this as I read the article. The notion of species is useless in understanding the phenomena the article discusses.
I'd go so far as to say that the word "species" causes significant confusion even among scientists, since it so biases the way one thinks about collections of similar organisms.
My hunch is that the "species bias" comes from the heavy influence of religious views of "creation" rather than "emergence" in Western culture.
My, layperson, understanding is that if they can interbreed and produce fertile offspring, then they are the same species. So two types of fly that can't inter-breed would be classified differently.
I don't think that's quite accurate (for example, ligers are capable of reproduction, though they would never be born 'naturally' due to the vast geographical separation of lions and tigers in the wild) but it might point you in the right direction.
For a long time, that was also my impression. But it's wrong. Mostly.
It turns out that there isn't a single definition for the word species—there are multiple definitions that lead to different results. Reading through the Wikipedia article about species will give you a sense of the different definitions. http://en.wikipedia.org/wiki/Species
If you use the Biological/Isolation species definition, I think you could argue that humans are or were multiple species. (Please, someone correct me if I'm wrong on this.)
My summary: collaboration between individuals is a strong Darwinian driver of competitive advantage between species (or other large groups). Homo sapiens individuals were more efficient at collaboration due to language and other social cognition. And yes, we (likely) killed the others off, like we have (possibly) killed off other large mammals (american giant ground sloth, perhaps).
They went extinct because we "outcompeted" them? If so, there would presumably be other creatures, competing for the same limited resources as us, that also went extinct at the same time.
I thought the accepted theory was that we directly killed them off. Though... I suppose that conflict could be caused by competition for resources, as are many wars.
We kill each other based on skin color, village, accent, or religion. I don't find genociding a different species all that surprising. In fact, I expect it.
Don't you think it's surprising that some pocket of non-homo sapien humans didn't manage to survive on some remote island without getting found until at least after reasonable boats were invented (~5000 years ago).
Apes and humans exist in different ecological niches, they do not directly compete with one another for food, shelter, resources, etc. This is not true for different human species.
My ignorance of anthropology is definitely showing here, but how can an anthropologist make assertations such as "'The Homo erectus brain did not devote a lot of space to the part of the brain that controls language and speech,' said John Shea, professor of palaeoanthropology at Stony Brook University in New York."? Is it just from skull sizes and shape? Maybe there is far less diversity across skull size and shape in homo sapiens sapiens than I assumed (at least within the brain casing). I'm genuinely curious as to how we can know so much about these species.
Following a link below, I noticed that the genome of homo neanderthalensis (or homo sapiens neanderthalensis) had been sequenced. I imagine that this would allow such knowledge of brain structure.
Humans act a lot like apex predators in their environment (e.g. Lions in the Serengeti, Wolves in Yellowstone). It's just that our environment happens to be the entire planet.
We dominate the food supply such that only animals that stay out of our way and survive on a food supply that is unappealing to us can survive.
In addition, we kill competitors and handle all threats with aggressive tendencies. Finally, when all non-human threats are eliminated, we turn on each other.
I think the reason that we think there's only one human species is because current definition of "species", the biological classification sense, may not be complete enough to take the different races (3 main) in consideration; Caucasoid, Mongoloid, Negroid. Some experts consider these races as sub-species, but doesn't that inherently mean that there are differences?
If they aren't too different then we have sex with them, and if they are too different we kill them. We can project the future of our species using our awesome minds that can conceive of a "self", "species", and "time", and we deal with perceived future threats to our species in quick and ugly fashion.
Imagine, with all the racial issues we already have today with our Homo Sapiens group, if we had to share the planet with Neanderthals and Homo Erectus descendants, 2/3 the brain size of us. Would we give them the same human rights?
Could Sapiens have genetically dominate genes, and through breeding and competition wipe out the others? Do we have proof that the others like Egaster could have moved as far as we have, from sub-Saharan Africa to Iran, Siberia, Alaska, or from Iran to Indochina, Australia, Fiji and Chile?
A better question is: "Why are humans one of the LEAST diverse species on the planet?" The diversity of a species can be charted, and I would like to see a chart plotting that diversity. Humans will be on the edge of that chart, but I assume there will be close 2nd. Then the question will be, why is there only ONE species X?
The genetic difference between two of the most distantly related humans is actually less than that of a typical ape family. This leads geneticists to estimate that our species went through a bottleneck about 70,000 years ago when there must have been less than 20,000 humans alive.
Furthermore, for specialization to occur usually requires isolation and a whole lot of time for mutation and differential selection to occur. The human race is branching off into different species of human to this day, just give it another 50 or 80 thousand years and there will be multiple species of human.
Humans dominated this planet inside 10 thousand years, in evolutionary time frames that is a blink of an eye.
"just give it another 50 or 80 thousand years and there will be multiple species of human."
That isn't as clear as you might think. At the moment, we've returned to the entire human species living in one gene pool, one that spans the entire globe. We'd have to lose the ability to cross the world in timeframes on the scale of a human lifetime, and even if you postulate a total civilization collapse and a total loss of all knowledge, we know that civilization could return to an Age of Exploration-level of capability in a mere few dozen generations even under the absolute worst case scenario that still has humans left to talk about at all. Speciation under such circumstances is certainly not automatic.
However, talking about human speciation without accounting for the extraordinarily high chance that it will end up being driven by human intelligence is probably a waste anyway. Again, on the tens-of-thousands-of-years time frame, even if our civilization completely and utterly collapses, another one could arise on that time frame quite comfortably. (Civilization #2 faces some resource issues, but with enough time they can still be overcome.)
You can look at history as well. Australian aboriginal homo sapiens were isolated for 40,000-50,000 years or so without any speciation.
You'd need an isolation event and a VERY long period of time; we have much more control over our environment than the aboriginals, which would probably serve to minimize differences in selection pressures between isolated populations to a far greater degree. 50,000-80,000 years doesn't come close to long enough, IMO.
If brown dwarfs and giant wandering planets are as prevalent as we think they are, then there's almost always a port of call for humanity only 2 LY away for large swathes of the galaxy. If we can figure out how to create "seeds" of our civilization that are reasonably compact, we can send them across that distance in only a couple of decades using laser sails and other propulsion schemes not limited by the rocket equation.
I find the theory of Neanderthal predation (NP theory) of homo sapiens, set forth by Danny Vendramini[1], to be persuasive. It explains the genetic bottleneck in an elegant and intuitive fashion, along with a host of other related anthropological questions. In fact, it kind of opened my eyes to how much of human behavior and morphology deserves an explanation and could possibly be explained by a central selection pressure.
One epiphany that played a role in confirming my fondness for the theory surrounds the so-called Neanderthal Late Flowering. I'd never heard of this period before reading Vendramini's book, but while reading, based on NP theory, I wondered to myself why such a thing had not happened, as it would seemed to have been predicted by the theory. Theories need to have predictive value to test them of course. As it turned out, the last few chapters discussed a Late Flowering, and I was a bit blown away.
Also, within a few months of reading the book, a genetic analysis study came out which showed we have a small percentage of Neanderthal DNA (but, importantly, no female DNA) another crucial prediction of NP theory.
Anyway, it was a fun read by a talented amateur anthropologist. I recommend it.
you must be kidding. Check biology basics about predation.
The NP smells like Hollywood - big fury half-human looking monsters preying upon us and raping our fine women. Until a few of us left. And we gathered our strength and pushed back and revenged.
It's hard for me to believe that bottleneck's recentness makes NO difference in the likelihood of the current observed amount of diversity (which is what "entirely contingent" means to me). I can buy "mostly", of course.
It makes me wonder if our relatively little diversity is related to the uncanny valley and our ancestors eliminated any variation that wasn't enough like themselves.
The human response to diversity seems to be "KILL KILL KILL" unless mental effort is employed to override this natural response. I've wondered for a long time if there are no other hominids, and so little diversity in our own species, because we killed them all. Genocide seems to be in our natural emotional structure.
But I wonder if this could be related back to the bottleneck. During a bottleneck, inbreeding-related genetic disorders become an issue. Maybe evolution selects for genetic "purging" behaviors during such bottlenecks as a means of ensuring fitness... basically during the bottleneck you'd become Nazis to escape the effects of inbreeding, and these impulses might stay afterwords.
So your theory is that, to avoid inbreeding, we developed a "KILL KILL KILL" response to differences and diversity. Somehow, I don't think that that makes sense, unless you're thinking of it as a way to get societies to reject people born as a result of inbreeding. Neanderthal predation is a much better explanation, at least in my opinion: a intrinsic fear of things that look very like us but different because, not so long ago, things very similar to us were trying to kill and rape[1] us.
[1] Ellyagg mentions a study that showed that humans have some male neanderthal DNA, but not female neanderthal DNA. This, to me, suggests rape. http://news.ycombinator.com/item?id=2688389
Another point is that humans change environment to adapt, while other species must change themselves to survive.
Hence we are not diverse genetically, but our technology evolves rapidly.
Also, why is it that only humans can 'think'? Animals have 'instinct' for their basic survival and some (dolphins, orcas) are more equal than others, but only humans have a 'mind' to 'think'. Hmm..
Surprising, and highly unlikely. If it's not too taxing for you, you could read the rest of the Wikipedia article to better understand when measures other than reproductive compatibility are employed.
The suggestion that color alone would be employed by modern biologists to differentiate species, to the exclusion of other more important factors, is specious.
When they find the remains of midgets 10000 years from now would they also call them 'other species'? I never read any real proof of other 'human' species. Only 'possibilities' and 'believes'.
There are things I think most HNers basically take for granted (at least I do): the theory of evolution closely matches reality, all animals that ever existed on Earth (including humans), are subject to it, and basically all life on Earth is a big family of more or less distantly related cousins (you don't even need the fossil record for this one, DNA is enough).
This article doesn't challenge that. In fact, the idea that our hominids ancestors split in several cousin species flows quite naturally from the above assumptions. Now the question it raised is, why we don't have closer cousins than chimps? We may not unique in that respect, and the big gap between us and our closest cousins may not be that much surprising. But given that our ancestors and elder cousins colonised most of the world, wondering what happened to them is an interesting question, if only to understand how a thriving specie can go extinct.
Now, basic rationalist question: How do I know that?
Well, it's a bit complicated. First, as a child, I was interested in science. I had few religious influences (I only attended church at Christmas). The History I'm aware of tells be that Science is to date the most successful way to describe our world, and the engineering successes I see every day tells me that it indeed works. For instance, the computer I'm typing on right now depends on a fair bit of science. Most of it is magic to me, but I'm confident I could find a comprehensive explanation on the Internet. Science also just makes plain sense. I "get it" when I read science aimed for lay people.
The bottom line is, I trust scientists. I trust journalists that talk about science a bit less. I trust settled science best. I acknowledge that the current state of the art is probably mistaken on many many things, but I'm confident that subsequent discovery won't shake the foundations of everything we know, though we may discover earth shaking new things. (For instance, relativity is a refinement of Newton's theory, not a complete revolution. It confirmed that under "ordinary" conditions, Newton's theory will give almost exact results.)
This particular article looks like a journalist's report about a bit of reasonably settled science, that just makes sense. Therefore I trust it. On the spot. No need for further proof.
> H. ergaster could also travel and hunt in the middle of the day, when most animals rest.
I'd rather say "when most other animals rest". The article recognizes we're not ontologically special, but there are still traces in the phrasing.
?!? Downvote? What could that be for? I'm just pointing out a minor contradiction. I may be a little off topic, but that hardly clutters this small page. Or is this because we are ontologically special (having immaterial souls)? But then (1) I didn't say that, and (2) current evidence doesn't actually support that.
If I could downvote, I would, because 1) Your point is ridiculously minor and not supported by the article, 2) you whine about being downvoted, 3) you assume bad faith everywhere.
I accept "minor" (but not "ridiculously"), and point 2. As I said in comment http://news.ycombinator.com/item?id=2687417 I understood my comment wasn't clear enough. My edit should have added clarifications, not whining. Sorry.
I deny point 3. The probability I assign to downvote due do religious disagreement is very low. I was nevertheless surprised. My comment was the second ever written on that thread. It was very short. It wasn't really meant to spur answers. And the contribution, though very small, is real.
I don't understand "not supported by the article". It explicitly talks about the continuum between Homo Sapiens and all other Homo species. If they hadn't disappeared, we could have seen it, and may have revised our long standing assumption that we are special among all animals. In that respect, they do recognize we are not so special, at least not a priori special. But still, they used the vocabulary in a way that does assume we are a priori special. All this is pretty obvious for me, but I suppose that "Humans are animals" is not a thought that most cache. http://wiki.lesswrong.com/wiki/Cached_thought
You're overly zealous to push this point. That phrasing does not at all imply that humans are "special," nor that they aren't animals. Here's a precisely cognate sentence:
I am asleep at 10 a.m. on Fridays, when most people are at work.
OK, maybe I wasn't explicit enough, then. I wanted to stress the fact that, even though most atheists completely accept that humans are animals like any others, just with "bigger" brains, there is still vestiges of the time where we thought it was not the same at all.
Some of those vestiges can be found in our language. Here, it was saying "human and animals" instead of the more correct "human and other animals" (without the emphasis of course). This kind of phrasing tend to promote the higher status of humankind as self evident, while frankly it is not. (I've read once that Dolphins may be almost as sentient and sapient as we are. In this case, they should have right they currently don't have.)
We now know that making up a category that includes all fishes, insects, birds, reptiles… and all mammals (including apes), but Homo Sapiens and some of its now extinct cousins isn't reasonable.
Unless of course if you believe that humans have immaterial souls and animals do not. That would make us very special. But the probability I assign to this possibility is negligible.
Even biologists have such a category: They call it "non-human animals". You might argue that this category is not generally useful, but it's not "wrong." That is itself a sort of superstition.
Well, at least by putting "non-human" in "non-human animals", they understood that human shouldn't be excluded by default.
By "wrong" I essentially meant "you shouldn't do that", here because it is misleading. Using the single word "animal" when you actually mean "non-human animal" suggest we humans are not animals. We are.
Now you changed my mind a bit: the "non-human animals" category does have its uses, and it does make sense to think of it. I just think it doesn't deserve the shorter expression "animals".
(I've read once that Dolphins may be almost as sentient and sapient as we are. In this case, they should have right they currently don't have.)
Like which ones? The useless (to dolphins) ones such as freedom of speech or owning property, or the ones many humans don't have like kind treatment and living in an uncontested land like they used to?
The second kind of course. Priority should still be given to humans (if only because it's my specie), but we should keep in mind the other animals, especially the most advanced ones.
I suspect however that once the world treats its humans well (if ever), then the other animals will also be in much better shape.
When we talk about Homo ergaster and Homo erectus it doesn't do justice to the significant variation among, and geographic distribution of, the fossils that are grouped under these species names. It's hard to know which variation can be accurately attributed to intra-species variation or sub-species or even separate species.
However, what is clear is that there is a great deal of variation in Africa, Asia, and Europe around the time of the "eretines". My feeling (back when I was a student) was that the archaeological evidence suggested an ongoing adaptive radiation of sorts, rather than the classic picture of a steady and relatively homoegeneous trajectory towards modern humans. But a lot of new research has been done since then that I'm not up to speed on.
Prior to the displacement and extinction of the remaining human forms there was already a reduction in the number and variation of Homo species. Even within our own species, there was much greater variation some 200-150kya.
There aren't any easy (accurate) answers to these sorts of questions, which is also why they are such fascinating areas of research. Understanding all the factors and events involved is very difficult with the type of information available.
You just have to look at the incredible lack of hominid (great ape) fossils for the last many million years of years to see know how difficult it can be to piece together an evolutionary history of a taxonomic group.