Humans Evolved From a Single Origin In Africa 461
Invisible Pink Unicorn writes "Researchers at the University of Cambridge have combined studies of global human genetic variations with skull measurements worldwide to show conclusively the validity of the single origin hypothesis. The alternative hypothesis contended that different populations independently evolved from Homo erectus to Home sapiens in different areas. The lead researcher explains, 'The origin of anatomically modern humans has been the focus of much heated debate. Our genetic research shows the further modern humans have migrated from Africa, the more genetic diversity has been lost within a population. However, some have used skull data to argue that modern humans originated in multiple spots around the world. We have combined our genetic data with new measurements of a large sample of skulls to show definitively that modern humans originated from a single area in Sub-saharan Africa.' The article abstract is available from Nature."
Not so fast (Score:5, Informative)
"John Hawks of the University of Wisconsin-Madison says the paper is mistaken. A major flaw is that the current research is largely based on skull variability. "You can't find the origin of people by measuring the variability of their skulls," Hawks said.
"Differences in skull features are related to genetics, and genetic variation depends on how much mixing occurs with other populations. "The main problem with the paper is that it takes some assumptions from genetics papers of 10 to 15 years ago that we now know are wrong," Hawks said.
"Other scenarios, besides the single-origin theory, could account for the link between distance and skull variability. "Africa is ecologically diverse, and cranial variation is a function of environments," he said. In environments supporting hardy foods such as roots, people would need bigger jaw muscles, and thus larger areas for muscle attachments.
"Also, correcting for climate is not a good idea, according to Hawks. "The most important feature that is related to climate is skull size. So by correcting for climate, they are subtracting a major component of variability," he said.
"In his own research, Hawks is finding that natural selection has led to changes in thousands of genes during only the past few thousand years.
"I'm really thinking just the opposite of this paper," Hawks said. "There are differences in the skull between populations, including their variability, but it is mostly due to very recent effects and not the origin of modern humans."
"At the end of the day, a resolution to the "Out of Africa" debate may be impossible, he said. Most of the evidence can be interpreted as supporting both human-origins theories. "It's really hard to find observations that distinguish the two," Hawks said.
"The multiregional idea is identical to the recent African origin idea, except for its prediction that Europeans and Asians were part of the single population of origin and didn't become extinct."
Re:One source for all life (Score:1, Informative)
- Even if life reoccurs at a different time, one type is likely to be vastly superior and outcompete the other.
Re:One source for all life (Score:3, Informative)
Re:Not so fast (Score:5, Informative)
It looks like my OP is going to be modded -1 Troll anyways, since some people seem to think that there are only 2 theories: Evolution and Creationism, and that if I'm saying "Not so fast", I must be spouting creationist nonsense.
Hilarity ensues.
Re:Not so fast (Score:4, Informative)
Re:Not so fast (Score:5, Informative)
Re:Um, why is this even in question? (Score:2, Informative)
Of course, the amount of time required for populations to become reproductively incompatible would be augmented by the rate of evolution of those populations, so the figure above is only for a baseline situation. High rates of mutation and heavy selection pressures could speed up the process.
Re:Not so fast (Score:5, Informative)
Re:One source for all life (Score:1, Informative)
Re:Not so fast (Score:3, Informative)
stupidity supports racism (Score:3, Informative)
Because there really was just one source (Score:5, Informative)
Yes, and that ancestor is a very simple RNA-based bacterium. And this evolved into DNA-based simple bacteria. Then bacteria which included other simple and ultra-specialized bacteria (cloroplasts and mitochondria). Which evolved into simple multi-celular life forms like sponges and extremely simple worms (hardly more than essentially an elongated torus whose surface was a bacterial film.) Which further evolved into more and more complex stuff.
And some figured out how to eat the others. E.g., fungi evolved to take another cell apart for food. And then some of those managed to, well, more or less do agriculture with other bacteria: the lichen are more or less a combination of a fungus and a bacteria, where the fungus traps the bacteria and helps fixate water and minerals for it, then scoop the food the bacteria produced. Or sometimes just destroy and eat those bacteria for food.
So there you already see the early split between plants and animals: one branch of the fork relied on photosynthesis to produce its own food and energy, using solar energy for it, and the other branch of the fork evolved to be basically parasites on the first one. Whether literally parasites eating the live plants (mostly plankton and algae at that point), or eating the corpses.
But before that fork, they evolved from the same ancestor, hence why they're still similar inside.
And from there it was often a race between species, driven by natural selection. E.g., the lignin based plants of the carboniferous era had a major temporary advantage, in that bacteria and fungi didn't yet exist which could digest this adaptation. However, that also applied to dead plants, which is why there's so much coal left from that age (and gave the age its name.) There simply was noone around which could eat a dead plant. But then bacteria evolved that could take apart lignin and celulosis. And then some animals evolved compartmented stomachs where they could store such bacteria so they could eat plants. (Don't think just literally animals. Some insects, e.g., termites, do exactly the same.)
And so on, an so forth, branching wildly ever since, and punctuated by some extinctions that trimmed the tree.
But, yes, once you trace all the branches back, it all leads to that first primitive bacterium. That's why it's all so similar at a chemistry level. Each step was a tweak of what already existed. Each step evolved more complex proteins, or just different proteins, and more specialized roles, but it was still based on the same reactions that worked before.
E.g., it still had enzymes which copied a strand of RNA, between a "START" and an "END" marker, to a protein. Even in DNA based cells, it's still not that horribly different: there's just an extra step of transcribing the DNA to RNA, so then you can transcribe the RNA to a protein. (As to why that more complicated mechanism evolved by natural selection: because breaking a single strand of DNA, for example by radiation or some chemicals, can still be fixed, while the same break in RNA means cell death. So the DNA based mutants were hideously more survivable than their RNA based ancestors.) Anyway, we essentially we still use the same mechanism of producing the proteins as that original proto-bacterium ancestor.
Where did that original bacterium come from? Well, probably from something even simpler. A bacterium is nothing more than a drop of sea water with a membrane. It makes it easier to keep the contents isolated from the rest of the world, much like a test tube does. But ultimately you just have some reactions in liquid water inside. So probably some chemica
Re:At least wait for the ID people to post ... (Score:2, Informative)
Y-chromosomal Adam [wikipedia.org]
Mitochondrial Eve [wikipedia.org]
Re:Not so fast (Score:3, Informative)
That's now how it works. "Turning into humans" (or any other species) is a long, involved process that entails some random genetic mutations being advantageous enough for you to spread them around. Then there's some separation that blocks interbreeding between populations. Evolution continues in both populations until they speciate--i.e. they can no longer interbreed because they have separately evolved for long enough. While parallel evolution does happen, the "parallel" species are still different species and can't interbreed. The probability that the exact same series of mutations would happen in even two separate populations is absurdly great, to say nothing of the countless different populations that would arise globally.
Another vague way that could happen is if there were interbreeding between nearby tribes of hominids. This is known as a ring species, and if humans were a ring species, then you could only interbreed with people who descended from your general area. Turks and Arabs could interbreed, and Greeks and Turks could interbreed, and maybe even Greeks and Arabs could interbreed some of the time, but none of them could interbreed with Koreans. This isn't how humanity is--all human populations can interbreed.
Re:Not so fast (Score:3, Informative)
It seems here that we have a researcher who started with a conclusion and is trying to find data to support it, rather than starting with a hypothesis, gathering data, and forming a conclusion
While I don't know much about the research in question, this statement struck me as wildly wrong. Theories are quite often developed before there's data to support that theory. The most well known of those is special and general relativity. At the time Einstein created these theories there was very little data to support it. General relativity might have accurately predicted the orbit of mercury where newtonian physics didn't, but that wasn't the only explanation at the time. The data to support relativity was only produced after people started looking for it. You're correct though that much of science has theories to explain evidence previously gathered. You're wrong that science doesn't work the other way around though. It happens all the time.
And it had astronomically many tries (Score:3, Informative)
That said,
1. While chlorophyll does match that spectrum well, the original photosynthesis was done by cyanobacteria, which _don't_ match that spectrum too well. So there you go, a less perfect solution was perfectly viable too, and the better solution appeared later.
So give me a break with the "too many things had to be just perfect" ID speech. Non-perfect partial solutions exist everywhere. Cyanobacteria themselves didn't disappear even after better tuned plants appeared, and are still around. They still exist and even specialized fungi exist which form lichen with the less efficient photosynthesizing bacteria. So you don't even have to guess or look at fossils there. The partial solution and intermediary step still exists.
2. I'm not sure if perfectly adapted to an atmosphere of oxygen, which is what we have now, is the same as perfectly adapted to an atmosphere of methane, which is what life started with. The argument that everything had to be designed just perfect isn't very believable, when you look at the fact that conditions were different in the first place, and changed _massively_ in the meantime.
3. "Astronomically small" chances happen eventually, if you have astronomically high populations and astronomically high time. When you have populations of trillions of trillions of bacteria, suffering mutations all the time, over a billion years, eventually one _will_ hit jackpot. Especially RNA based bacteria suffered a hideously high rate of mutations, and diverged very very fast in all directions.
As they say, "if you're one in a million, there are six thousand just like you". _That_ is how large populations and small chances work.
Let me give you an even more improbable example. Rolling 20 dice and rolling all sixes is incredibly improbable, in fact, 1 chance in 3,656,158,440,062,976. But if you had a billion people rolling dice once a second, it would only take on the average 3.6 million seconds or 1000 hours for that to happen. That's a little over a month. And when dealing with bacteria, a billion of them is actually an incredibly low population.