Why is there only one human species?
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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.
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.
Why do you call it "incredible"?
[1] http://afp.google.com/article/ALeqM5g-BDjcKrIh9YFbsqsJiky6m2...
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.
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.
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).
That was probably the first time we transcended ecology. We keep on pulling this trick.
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 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 :)
edit: wikipedia and google searches haven't revealed any positives. Thanks for that link though, very interesting.
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.
I'm sure if we really thought long and hard...
See: http://www.nature.com/nature/journal/v293/n5829/abs/293181a0... -- http://localhostr.com/file/itFWMaa/zzz.pdf
"it can be estimated that at current rates each kilo of insecticide added to the environment will generate 105 new cases of malaria"
In short, it just ain't that easy.
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.
I guess this could also be the cause of racism.
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.
The margins for survival are very slim. Out-competing through more effective hunting and gathering would make a huge difference.
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).
Homo floresiensis ("Flores Man", nicknamed "hobbit") is a possible species, now extinct, in the genus Homo
Also, I like the mythical cyclops could have been from dwarf elephant skulls theory: http://www.users.globalnet.co.uk/~loxias/cyclops02.htm
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.
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.
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.)
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.
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.
So it would be more accurate if you had written "humans and other apes".
You knew what he meant, so clearly that is not needed.
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.
We got ahead because we developed the first mesh-net -- spoken language . . . free and unencumbered by artificial legal restrictions like copyright.
The more richly you communicate, the more advantage. Newspapers with pay-walls, and such like -- the Homo-erectus of now.
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.
http://storify.com/devonvsmith/games-for-change-jesse-schell...
P.S. The whole talk is worth listening to when it eventually comes out.
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.
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.
[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
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.)
Interstellar colonies, then?
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.
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.
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.
"differing measures are often used, such as [...] morphology"
Okay. Please enlighten me as to the meaning of 'morphology'?
Morphology "includes aspects of the outward appearance (shape, structure, colour, pattern)"
So two organisms classified into different species might only differ in terms of outward appearance, such as colour? Surprising.
Thank you Wikipedia, you may go now.
The suggestion that color alone would be employed by modern biologists to differentiate species, to the exclusion of other more important factors, is specious.
Bad stuff happened to us too, but we got over it.
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.
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.
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.
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".
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?
I suspect however that once the world treats its humans well (if ever), then the other animals will also be in much better shape.
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
I am asleep at 10 a.m. on Fridays, when most people are at work.
Does this imply that I am not a person? No.