Evolving Toward Humans
Chapter 20: IMAGES FOR LECTURES
Updates for Chapter 20.
NOVEMBER 2006. A human gene complex that is not ours. Is it Neanderthal?
SEPTEMBER 2006. The fossil of an Australopithecus afarensis child (maybe 3 years old).
OCTOBER 2005. Homo floresiensis. This is a new, very small species of Homo from the island of Flores: and only 18,000 years ago, maybe less! Or is it a Homo sapiens with a birth defect?
FEBRUARY 2005. The oldest Homo sapiens is reliably dated at 195,000 years ago.
NOVEMBER 2004. Running as the major breakthrough that marks the appearance of Homo.
Invader genes in many living humans. About 70% of living humans have a set of genes that help to control brain development, yet they are not from our own genetic heritage. They must have come from some other Homo in the past. The candidates include Neanderthals. The implications are fundamental, and yet to be fully explored. Fortunately, the paper is on open access.
The A afarensis child. Article by Kate Wong for Scientific American. September 20, 2006.
Homo floresiensis. This is a very important find, and we will be trying to work out the implications for a long time. The two papers in Nature from October 2004 are not freely available on the Web, but Nature did post several stories and comments, listed below.
I had an astral communication from the young lady in question. The translation software delivered it in the unmistakable form of a limerick, which I transcribe below. It's not the best limerick in the world, but what can you expect from someone who a) isn't British; b) has been dead since the Stone Age; and c) has a brain half the size of a can of Budweiser.
I'm glad that you're telling new stories
About us, the first people of Flores,
We weren't very tall,
Our brains were quite small,
But our diet was elephantivorous.
But seriously, folks... There are two dramatically opposed interpretations of these fossils. One is that they are deformed ("pathological") humans; the other is the one that the original discoverers argue: that they are a separate species, evolved by dwarfing on the island of Flores. There is no resolution of the issue (in March 2013), but opinion is ever-so-slowly swinging toward the acceptance of the Flores people as normal Homo of some species or other, but definitely dwarfed by island evolution.
The oldest Homo sapiens is reliably dated at 195,000 years ago.
By dating a "modern" skull (Omo 1) at 195,000 BP, the origin of the modern sapiens body (especially the skull) is pushed back even further, before any evidence of "modern" human behavior. It begins to look as if these ancient sapiens were quite variable (they would include idaltu), which is interesting but not surprising.
Running as the major breakthrough that marks the appearance of Homo.
The paper is Bramble, D. M., and D. E. Lieberman. 2004. Endurance running and the evolution of Homo. Nature 432: 345-352. Here are some news reports. BUT read the paper: it's completely convincing.
Notes and general links
Small jaws and big brains in human evolution.
We know that modern humans have small weak jaws and big impressive brains compared with our closest living relatives, the chimps. Fossil evidence puts the transition between 2.5 Ma and 1.7 Ma, in the transition from one or other species of Australopithecus to Homo erectus, with two or three species events in that million-year span.
The authors of a new study (March 2004) have found a genetic difference between chimps and living humans. Humans lack a gene which turns on powerful growth of the masseter and temporalis muscles that work the lower jaw in chewing. But when was that gene lost? Chimp ancestors and our ancestors diverged maybe 7 Ma, and you can't do genetics on old hominids. The authors magic their data into giving a date of 2.4 Ma for the mutation that allegedly gave our ancestors suddenly weak jaws, and they then call on weak jaw muscles to allow growth of a big brain.
Now geneticists don't do evolution very well. Certainly this group talks about "an abrupt evolutionary alteration in the size and ...force" of chewing muscles, and they talk about "effects on craniofacial morphology in the first homozygous [mutant] human ancestor" [I added the bold face]. They are using the old "hopeful monster" kind of argument.
Now the fact of the genetic difference is real and important. But the interpretation of the authors is terribly naive. So I'll tell you what really happened‹for free‹and it's worth every penny you paid for it. Remember that there are regulatory genes that turn structural genes on and off (Chapter 4).
The suite of discovery, innovation, and increasing intelligence that gave some australopithecine a better ability to hunt, prepare food, and so on, happened perhaps around 2.5 Ma at a brain size that was typically australopithecine (evidence: A. garhi and/or A. africanus). That suite changed the diet toward meat, higher protein, less chewing, etc., and at some point the evolving jaw reached a morphology where the Big-Muscle gene wasn't being turned on much at all; it was turned on only enough to give typically Homo jaw muscle size. Any time after that, the Big-Muscle gene could be lost without penalty ‹ and without any obvious morphological jump in the skull. The larger brain came later, but it perhaps came more easily because the jaw musculature was smaller.
You can see that this story is not far from the one the authors put forward. The difference is that mine is truly evolutionary (it happens over a long time); it does not demand a Hopeful Mutant; it does not call for an Event; and it is not tied to statistical magic that gives a one-time miracle.
The paper is in Nature, so is not freely available on the Web. Stedman, H. H. et al. 2004. Nature 428: 415-418; and uncritical comment, pp. 373-374. News story:
University of Pennsylvania press release
The Appearance of Homo
Early species of Homo
Images of early Homo:
This is the skull KNM-ER-1470. It is sometimes called Homo rudolfensis, and is on this Web site, but many people put it together with Homo habilis. (If so, it may be a large male skull.) The skull could have been reconstructed in a subtly different way that would have made a difference in both appearance and interpretation. This is a common, perhaps underestimated problem in reconstructing and understanding all fossil vertebrate skulls.
This skull is KNM-ER-1813 from East Turkana, usually called Homo habilis. It has a small skull for Homo, (possibly it is female?), but Homo teeth. This is another example of a problem that recurs in paleontology. Although the fossil does not change, ideas may change or errors may creep in.
Homo from Dmanisi, Georgia
Overview of Dmanisi hominids from Scientific American, Fall 2003.
Web note by John Hawks, March 2005, pointing out that the Dmanisi hominids not only has habilis-sized brains, but habilis-sized bodies as well.
The 2002 publication. Vekua, A., et al. 2002. A new skull of early Homo from Dmanisi, Georgia. Science 297: 85-89, and comment, p. 26-27. This skull is around 1.8 Ma. Other skulls from Dmanisi from the same beds have been assigned without much controversy to an early Homo erectus lineage that had recently migrated out of Africa. The new skull is small, and has more primitive features, more like Homo habilis. So what do you do? It seems really far-fetched to suppose that two species were living there at the same time, so these authors suggest that the population was variable, but was all the same species, an early Homo erectus. The tools are sort of Oldowan-looking. I love it.
The 2005 find: a Dmanisi individual was cared for in old age, 1.8 million years ago.
BBC News OnLine
The paper is in Nature, which doesn't make its papers generally available on the Web. Lordkipanidze, D., et al.: The earliest toothless hominin skull. Nature 434: 717-718. This individual had lost all of its teeth except for one canine (I'll call him Bucky), but had survived the consequent deterioration of the tooth sockets and jaw bone. This virtually toothless individual must have been fed soft food, such as bone marrow, to survive. So the group must have felt for whatever reason that this was the right thing to do. Now it doesn't mean that Bucky was old in our terms: we don't know how long a "normal" life span was. [Rank speculation: I'd like to think Bucky was the geologist: someone with a unique skill that the tribe needed: in this case for making the tools that kept the group going!].
Intelligent blog by John Hawks.
For a flashy reconstruction of these Dmanisi people, see this National Geographic feature
Images of Homo erectus:
Tools of Homo erectus
In 1999 the Discovery Channel aired a series on research at a site in Eritrea, northeast Africa, about 1 million years old, which has yielded an enormous collection of tools probably made by Homo erectus. I did not watch the series. Here are Web pages for the first three episodes:
Homo erectus and wood-working
Discovery that stone tools associated with Homo erectus were being used to chop wood. Archaeology OnLine, January 2001.
Homo erectus and fire:
Richard Wrangham's cooking hypothesis. From the Harvard Gazette, 2002. I like the idea, but there's very little evidence for or against.
Evidence of human use of fire at Swartkrans, around 1.5 Ma. BBC News OnLine, March 22, 2004. That would be Homo erectus.
Human use of fire at about 800,000 years ago. BBC News OnLine, April 29, 2004. The paper is in PNAS, so it is on the Web (see new references for this Chapter). These are home fires, built in association with settlements in the Jordan Valley, in what is now northern Israel. At this date, the fires were built by Homo erectus. They used wood branches from olive and ash. A later paper established that among other things, they were making pita bread.
Asian Homo erectus.
Why did Homo erectus have such a thick skull?. Feature article in Natural History, February 2004, by Noel Boaz and Russell Ciochon.
Specimen Sangiran 2 from Java, the so-called Java Man. An Asian Homo erectus.
Homo erectus from Northern China, "Peking Man", looking cheerful.
Homo erectus is the earliest hominid species found outside Africa. Specimens from Java, in Indonesia, may be as old as 1.8 Ma. If these old dates stand up to further scrutiny, they imply that H. erectus left Africa almost as soon as it evolved there, before African erectus invented the Acheulian tool kit.
Recently, new discoveries have resulted in the claim that there are tools, made by Homo erectus, in China as early as 2.25 Ma. It's not clear that they are that old, but they could easily be 2 Ma. Either way, it looks clearer and clearer that Homo erectus evolved early and migrated early to Southern Asia. Here is a newsbrief from Archaeology, January 2000.
Undoubted tools have been found in NORTH China, dated around 1.4 Ma. This means that Homo erectus must have been dealing with very cold winters, and my prejudice is to shout "Fire!" However, there's no direct evidence.
Very well preserved and very well dated stone tools were made in China, presumably by Homo erectus, around 800,000 years ago. They are as sophisticated as contemporary tools being made in Africa. Story from BBC News OnLine.
Homo erectus at 780,000 BP in Israel. There are no bones, but there are thousands of characteristic tools and there's evidence of the use of fire. This is yet more evidence that there were significant migrations of Homo along the Africa-Asia corridor at really ancient times.
Someone, presumably Homo erectus, was cracking nuts with stone tools in Israel, 780,000 years ago. Press release about a paper in PNAS, February 2002.
Human use of fire at about 800,000 years ago. BBC News OnLine, April 29, 2004. Reference: Goren-Inbar, N., et al. 2004. Evidence of hominin control of fire at Gesher Benot Ya'aqov, Israel. Science 304: 725-727. Is now freely available on the Web here.
Homo erectus may have invented boats or rafts. Tools of H. erectus have been discovered on the island of Flores, in Indonesia, which has been separated by several miles of sea from the rest of Indonesia for at least two million years.
Homo erectus may have survived longer in Southeast Asia than we had thought.. From Archaeology, March/April 1997.
For a 1997 review of research on ancient seafarers in the southwest Pacific, see this article from Archaeology.
A new Homo erectus skull from Africa confirms that it was a single world-wide species (Old World, that is). The paper was published in Nature on March 21, 2002. This paper is significant not only because it establishes that there were not two co-existing species H. erectus in Asia and H. ergaster in Africa: there was one species. If THAT is true, it becomes even more likely that the predecessors of Homo sapiens were also a single interbreeding species. Sure we may be dominated by genes of African origin, but the concept of limited interbreeding is still alive.
The Origin of Modern Humans
Overview of the competing theories. by Michael Roberts. Updated July 2005.
What does Chris Stringer think?. He's at the British Museum of Natural History.
web essay by John Hawks, arguing that humans always had some gene exchange across their far-flung populations.
Human evolution is more complex than a simple "out-of-Africa". New research by Alan Templeton, published in Nature, March 2002:
Homo antecessor is a name given to fossils from Spain about 780,000 years old. Here are five items,
Homo heidelbergensisis a name that has been suggested for fossils (humans) transitional between Homo erectus and Homo sapiens, in Africa. They spread into Europe, and are named after a fossil found in Germany.
Here are some images:
Evidence from Germany around 400,000 BP suggests that H. heidelbergensis must have been formidable people. Beautifully crafted hunting spears were made by H. heidelbergensis in Germany around 400,000 BP. They are throwing spears, up to 3.2 m long (10 feet), carved to angle through the air like modern javelins, and they are associated with butchered horses and other bones from elephant, rhino, deer and bear. Here are two news articles on the spears:
An exquisite pink quartzite hand axe from 350,000 years ago. BBC News OnLine, March 26, 2003. Several things. First, this axe is an object of beauty, comparable aesthetically and functionally with the hardwood javelins made in Germany around the same time. Homo heidelbergensis, then, was a formidable species. AND if indeed this axe was placed with a pile of bodies in some sort of ritualistic gesture (rather than being dropped by accident), it implies a mental capacity for abstract thought that you might not expect to find in a Neanderthal ancestor: not, at least, if you are as sapiens-centered as many anthropologists seem to be!
Many anthropologists have cited "art" as a modern human characteristic. Obviously, these new discoveries show that that idea is just plain wrong. Either the older story of human evolution is right, and "archaic" Homo sapiens was evolving this early, or we have to recognize that Homo heidelbergensis (call it what you like) was capable of art and sculpture well as the design and manufacture of exquisite spears in Germany. This is more evidence, in my opinion, that something is radically wrong with the current emphasis on recent origin or radical innovation, or both, for Homo sapiens.
Around 200,000 BP, it is suggested, a population of H. heidelbergensis in Africa evolved into what we would now recognize as Homo sapiens. Meanwhile, Homo heidelbergensis in Europe and the Middle East were evolving into Neanderthals.
The Klasies River people of South Africa, clearly modern humans, and perhaps the earliest non-controversial modern humans.
When did human adolescence evolve? National Geographic News, December 2001. Late!
Neanderthals: there's enough information to justify a separate page: easy return to this page.
The earliest known Homo sapiens, from Ethiopia, around 155,000-160,000 BP. New report, June 2003. Science News
Early modern human from Skhul, in the Near East.
New Romanian fossils are the oldest Homo sapiens in Europe: stories from September 2003. The age is about 35,000 years old, which makes them contemporary with late Neanderthals. And the single jaw has very large molars, leading to the suggestion that there may have been some interbreeding (very much a guess, but not an impossible suggestion).
July 6, 2004. Human longevity evolved around 30,000 years ago. Press release about a paper to be published in PNAS. If true, this has astonishing implications. This is the time when modern humans took over from Neanderthals, for example. It also shows dramatic evolution within a species (however you slice it, these were not the first Homo sapiens by a long way): yet another nail in the coffin of punctuated equilibrium, for those who might still believe it.
So what makes humans truly human, if it's not bipedalism? Could it be (gasp!)... display? (Remember the origin of birds, Chapter 14?)
Out of Africa, and Molecular Evolution
Much of the current story of the appearance and dispersal of Homo sapiens (seen as a recent eruption of a few genocidal populations) rests on inferences from molecular evolution, especially for the timing of the supposed event.
And those inferences depend on the assumption that in studying mitochondrial DNA, we are looking at DNA that is not subject to much, or any, selective influence. Instead, changes in mitochondrial DNA are selectively neutral. It is only if you accept this assumption that mitochondrial DNA would change in a clock-like manner.
The analogy is with radioactivity. Radioactive decay proceeds randomly as far as each atom is concerned, but as a whole, a rod of radioactive fuel produces energy by atomic fission in an entirely predictable, clock-like fashion. That's why nuclear power plants don't randomly explode. Molecular biologists would love to have the same sort of predictable change-through-time that is provided to geologists by radioactive age dating (Chapter 2).
So a whole mini-industry has developed, producing "divergence dates" based on analyzing mtDNA in living organisms, always using the assumption that changes in mtDNA are mostly or completely attributable to non-selective changes.
The entire mini-industry would collapse, and its "divergence dates" along with it, if the assumption were faulty.
Well, folks, it IS faulty. Research published by Ballard late in 2000 reported an intensive study of the mtDNA in species and strains of the fruit-fly Drosophila (see summary by Rand 2001). Ballard has shown conclusively that mtDNA in Drosophila shows evolutionary change that is incompatible with the assumption of neutral or nearly-neutral selection. (The evolutionary change seems to be induced by strong natural selection associated with a parasite called Wolbachia that can entirely ruin the sex life of a fruit fly, but the specific source of the selection doesn't matter. What does matter is that mtDNA can undergo strong selection.)
Furthermore, there is strong evidence that mitochondria DO respond to natural selection IN HUMANS. As you might predict, the metabolic rate of humans might have a direct relationship with the climate they live in. Indeed, that is so: here is a press release from 2004
This is important on all kinds of levels. If any of you still believed that changes in mitochondrial DNA could operate as a uniform clock for evolution, you can now safely abandon the idea. If any of you still believed that significant evolution only occurred at species boundaries (punctuated speciation), you can now safely abandon the idea. If any of you still believed that evolution is not occurring now among modern populations of humans, you can now safely abandon the idea. If any of you thought that it was not a good idea to point out that different human groups may have different medical problems, forget that too. The paper is in Science 303: 223-226, so will be freely available on the Web in 2005.
So does this discovery ruin the conclusions based on mtDNA studies? No. Change in mtDNA can show evolutionary pathways and branches in the organisms that carry that DNA. What does become suspect is the idea that one can assign specific dates to ancient branching events. So in reading results based on mt DNA, or nuclear DNA for that matter, remember that any dates mentioned are likely to be wrong by some unknown factor: in other words, don't believe them for an instant.
Fight over DNA from Mungo Man, old Australian skeletons, January 2001. Mitochondrial DNA isolated from several specimens of Mungo Man is the oldest extracted from any fossils that everyone agrees are modern human. The mtDNA of several specimens is different from any mtDNA from living humans, and can be characterized as being "more primitive/ancestral" than anything African.
First, this shows that there are mtDNA lineages that have gone extinct, even though their possessors were fully members of modern Homo sapiens. So does the different mtDNA extracted from Neanderthals unequivocally bar them from membership in Homo sapiens? Some of the weaselly answers quoted in these news stories suggests that the answer may be "NO." For example, some of the "Out-of-Africa" folks are hedging their position by talking about a little bit of potential inbreeding. I suppose that if Neanderthal women were carrying children of "modern humans" they were only a little bit pregnant!
Mitochondrial Eve and Y-chromosome Adam.
Mitochondria are inherited in children only through mothers, and Y-chromosomes are passed on only to sons by their fathers. So I have my mother's mitochondrial DNA and my father's Y chromosome. My daughters have my wife's mitochondrial DNA, and no Y chromosome. Now let's do it backwards. All living humans carry mitochondrial DNA, and best estimates are that all that mitochondrial DNA probably descended from one woman (Mitochondrial Eve) who lived in Africa maybe 175,000 years ago ± some unknown error. All living males carry a Y-chromosome, and best estimates are that all Y-chromosomes descended from one man (Y-chromosome Adam), who lived in Africa maybe 75,000 years ago ± some unknown error. Why the gender difference?
Of course, there were untold thousands of humans living alongside these individuals. But lineages of mtDNA only pass through females, so if a woman has only sons, her mtDNA lineage goes extinct. If a man has only daughters, like me, then his Y-chromosome lineage becomes extinct. Over time, there may be only one lineage that survives from any given ancient population: and that is what the geneticists have reconstructed as best they can. Even so, why the gender difference?
That could arise in several ways. The most likely is polygamy: some men have several partners, others have none. Thus females, on average, will have more chance of passing on their mtDNA in any given generation than their male contemporaries. Y-chromosome lineages will fail faster than mtDNA lineages, so "Adam" will be more recent than "Eve".
For longer (and better) essays, see these two by Carl Zimmer:
Much is made of the very high percentage of DNA that humans share with chimpanzees, and the difference is one of the time markers using in calculating divergence of humans, on the assumption that that separation has occurred by molecular-clock (stochastic) mutations.
However, research published in 2000 looked at some of those genetic differences. The differences studied are certainly not random, since they affect sperm production. The pattern of differences cannot have arisen by random processes either. They are certainly adaptive, under natural selection, and they receive explanation that is to do with the different mating patterns of chimps and humans.
Genetic variation within Homo sapiens
In 1999, geneticists confirmed that the genetic variation within Homo sapiens is extraordinarily small. Chimpanzees have relatively much greater variation. One population of chimpanzees from Africa, made up of 55 individuals, had more genetic variation than the entire human race. Press release from November 1999 .
But what does it mean? The authors talked about a bottleneck early in the history of our species, when Homo sapiens passed through a very small population size. I suspect that scenario, though possible, has a more sinister alternative.
It is clear from the data from chimps and gorillas that a "natural" hominid species has a very much greater genetic variation than we do. It's therefore likely that Homo sapiens did too. What happened?
The molecular data (classical version) suggest that all living Homo sapiens are descended from a population that emerged in Africa, and expanded to populate Africa, and then, in the Out-of-Africa scenario, expanded to populate the world. Some new genetic evidence, for example, suggests that Europeans come from a very limited number of original ancestors. A now-gone URL, May 9, 2001, described research published in Nature.
But other populations of Homo were living across the Old World. These included Homo neanderthalensis, which descended from Homo heidelbergensis in Europe and the Near East; and Homo erectus in Asia.
There is some evidence that Homo sapiens interbred with Homo neanderthalensis in Spain, because we have found an allegedly "hybrid" child that was apparently living several thousand years after the "end" of the Neanderthals. See my separate page on Neanderthals .
That suggests that the Out-of-Africa populations of Homo sapiens, with their restricted genetic variation, met other members of their own species who did not realize that they were supposed to be a separate species. The Neanderthals may have been outside the (narrow) genetic envelope that "living Homo sapiens" lies within, but they were inside the permitted, normal, genetic envelope of a normal hominid species that we should call Homo sapiens. If so, Homo heidelbergensis belongs there too.
In turn, that suggests that in the end the Neanderthal contribution to ancient and modern Homo sapiens was lost, or it has not yet been sampled. (About 800 of the several billion living humans have been sampled for genetic studies like this.) One could ask about the Tasmanian islanders who were separated from Australia for 10,000 years yet retained complete interfertility with the rest of the species. (I do not know whether any Tasmanian genes have been examined, and there are no full-blooded Tasmanians left.)
And this leaves open the question of the Homo erectus populations of Asia...
BUT WAIT! In 2006 it was discovered that about 70% of living humans have genes that help to control brain development, yet they are not from our own genetic heritage. They must have come from some other Homo in the past. The candidates include Neanderthals. The implications are fundamental, and yet to be fully explored. Fortunately, the paper is on open access.
Malaria and Homo sapiens
Malaria is one of the largest health threats to humans today, especially in tropical and sub-tropical latitudes. It's caused by a protozoan that thrives in the human bloodstream. Two species of Plasmodium are the worst offenders. However, the genomes of the chief malarial parasites of humans are amazingly uniform worldwide, while their counterparts in Old World monkeys are quite variable. Why is this? The most likely explanation is that human malaria is a recent disease: a parasite jumped from a monkey to humans perhaps only 10,000 years ago, probably in tropical Asia (see below), and has not had time to evolve very much.
This has interesting implications if it is true. First, the putative genetic jump probably coincided with the (cultural) shift to agriculture, which produced more concentrated and more sedentary human populations close to water sources. Second, the notorious genetic changes in humans associated with malarial resistance (especially sickle-cell anemia, for example, in African and Mediterranean peoples) has to be ever more recent, well within the time span of Homo sapiens.
The most recent paper is Leclerc, M. C. et al. 2004. Meager genetic variability of the human malaria agent Plasmodium vivax. Proceedings of the National Academy of Sciences 101: 14455-14460. This will be freely available on the Web some time in 2005.
It is possible that malaria first arose in tropical Asia. Escalante, A. A., et al. 2005. A monkey's tale: The origin of Plasmodium vivax as a human malaria parasite. Proceedings of the National Academy of Sciences102: 1980-1985. This will be freely available on the Web some time in 2005.
Language: Hearing (and speech) in Homo.
A news item from BBC News OnLine, June 25, 2004. The paper is due to be published in PNAS, so will be generally available on the Web relatively soon. The study looked at ear bones from Homo heidelbergensis from Spain, a probable ancestor of Neanderthals but not of Homo sapiens. The ear bones suggest a hearing system tuned to the same frequencies as our speech, so the implication is that heidelbergensis also had some kind of speech. If so, then Neanderthals did too. And furthermore, if speech only evolved once, then the point at which it evolved is AT LEAST as old as the common ancestor of us and heidelbergensesis, which would be some variant of Homo erectus. Course, I said that in the book, but based on commonsense, not evidence. This paper gives some EVIDENCE, even if it is indirect.
Evolution among Humans Today
What do you mean? Evolution is still happening? Well, of course it is. It's been happening since before life began (see Chapter 1). Why should Homo sapiens be any different from every other species that has ever lived? What's more, there's plenty of evidence for evolution among living humans for anyone who cares to look.
The reference list for Chapter 20
Page last updated, April 8, 2013
Links last checked April 8, 2013.
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