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Kenyan Fossils Rekindle Debate over Early Human Diversity

The views expressed are those of the author and are not necessarily those of Scientific American.


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Koobi Fora fossils

The KNM-ER 1470 cranium, discovered in 1972, combined with the new lower jaw from Koobi Fora. The specimens are thought to belong to the same species. The lower jaw is shown as a photographic reconstruction, and the cranium is based on a computed tomography scan. © Photo by Fred Spoor

If I had to pick the hottest topic in paleoanthropology right now, I’d say it’s the origin and early evolution of our genus, Homo. Researchers know quite a bit about our australopithecine predecessors (Lucy and her ilk) and about later phases of Homo’s evolution. But the dawn of our lineage is cloaked in mystery. One question experts have long puzzled over is whether Homo split into multiple lineages early on, or whether the known early Homo fossils all belong to a single lineage. To that end, new discoveries made at the site of Koobi Fora in northern Kenya—one of the Leakey’s longtime fossil hunting grounds—are said to settle that matter in favor of multiple lineages. But some critics disagree.

The new finds—a partial face including almost all of the molars in the upper jaw, a nearly complete lower jaw and a partial lower jaw that date to between 1.78 million and 1.95 million years ago—bear on the identity of a famously enigmatic skull from Koobi Fora known as KNM-ER 1470. Ever since the discovery of the 1470 skull in 1972, researchers have struggled to place it in the human family tree. On one hand, at nearly two million years old it is the same age as H. habilis fossils from Koobi Fora and other locales in East Africa. The skull also shares some features in common with that species, which most researchers consider to be the founding member of Homo. On the other hand, 1470 is much larger than established H. habilis fossils, and differs from them in having a flat, long face, among other distinctive traits. Some experts thus assigned 1470 and some other fossils from Koobi Fora to a separate species, H. rudolfensis.

Meave Leakey and Fred Spoor

Paleontologists Meave Leakey and Fred Spoor collect fossils close to the site where the new face KNM-ER 62000 was found. © Photo by Mike Hettwer, www.hettwer.com, courtesy of National Geographic

But nailing down whether 1470 is a rogue H. habilis or a separate species has been tricky because no other skull shared that long, flat face and the specimen lacks teeth and a lower jaw to compare with other fossils. This is where the new fossils from Koobi Fora come in. In a paper published in the August 9 Nature, Meave Leakey of the Turkana Basin Institute in Nairobi, Fred Spoor of the Max Planck Institute for Evolutionary Anthropology in Leipzig and their colleagues report that the new face mirrors 1470’s face shape, although it is smaller overall. Inferring 1470’s upper jaw anatomy from the new face, the authors say the lower jaw fossils they found are good matches for the upper jaws of 1470 and the new face. (Scientific American is part of Nature Publishing Group.)

New mandible from Koobi Fora

The lower jaw KNM-ER 60000 after initial restoration but before the adhering matrix was carefully removed. © Photo by Mike Hettwer, www.hettwer.com, courtesy of National Geographic

“For the past 40 years we have looked long and hard in the vast expanse of sediments around Lake Turkana for fossils that confirm the unique features of 1470’s face and show us what its teeth and lower jaw would have looked like,” Leakey remarked in a prepared statement. “At last we have some answers.” The answers, in their view, indicate that 1470 and the new fossils represent a distinct human lineage from other early Homo fossils. This would mean that two Homo lineages lived alongside our ancestor H. erectus. H. erectus itself may have evolved from one of these two groups or another, as-yet-unknown group. The researchers did not formally name the new fossils from Koobi Fora, because of confusion surrounding the fossil that defines H. habilis, but they suggest that it may be appropriate to assign them to H. rudolfensis. Bottom line, they’re saying the fossils confirm that the non-erectus early Homo fossils in East Africa constitute two lineages, not one.

Although it may be hard to imagine sharing turf with another human species today, members of these ancient contemporaneous lineages need not have stepped on each other’s toes. In background materials distributed to the press the discovery team noted that chimpanzees and gorillas live in some of the same habitats. Both eat ripe fruit, but gorillas focus more heavily on tough vegetation than chimps do. “The early hominins [members of the human branch of the family tree] could have separated their neighborhoods in the same way,” the researchers explain. “They may simply have focused on different primary food items.” Exactly what these hominins were eating is uncertain, “but there are clues from the arrangement of the face and jaws that the newly described fossils, and the previously known [1470 skull], with their tall faces but shortened front tooth row, may have been focusing on foods that required chewing on the back teeth.” Analyses of the chemical composition of the teeth, as well as their wear marks, may yield further insights into what these hominins ate.

In an accompanying commentary Bernard Wood of George Washington University calls the new evidence for at least two parallel lineages in the early evolution of Homo “compelling.” Indeed he suggests that this chapter of our evolutionary history was even more complex than that. “My prediction is that by 2064, 100 years after [Louis] Leakey and colleagues’ description of H. habilis, researchers will view our current hypotheses about this phase of human evolution as remarkably simplistic,” he writes.

Other researchers are not convinced that the new Koobi Fora fossils show multiple lineages of early Homo co-existed. Adam Van Arsdale of Wellesly College, who has studied the 1.76 million-year-old H. erectus fossils from the site of Dmanisi in the Republic of Georgia, notes that in light of the considerable variation evident in the well-dated Dmanisi sample, the variation in the early Homo fossils from Africa can be accommodated by one species. In fact, the new Kenyan fossils show features in common with the Dmanisi ones, and thus help to link early Homo in Africa to H. erectus in Georgia, he says. In his view, all of these fossils—the habilis/rufolfensis ones and H. erectus–belong to one lineage.

“What the African assemblage lacks is a good sample from a single locality that shows variation. Instead you have lots of fragmentary, isolated specimens, all with temporal uncertainty, that show a huge amount of variation,” Van Arsdale explains. Whereas Leakey and Spoor see this variation as evidence for multiple concurrent lineages, “I tend to see this new evidence as making it harder to reject the idea of a single evolving lineage,” he says.

A more pointed criticism of the new study comes from Lee Berger of the University of the Witwatersrand in Johannesburg. Berger notes that in their paper Leakey, Spoor and their colleagues neglected to compare the new Koobi Fora fossils to Australopithecus africanus and A. sediba fossils from South Africa, which were contemporaries of early Homo from East Africa. (Berger led the team that discovered A. sediba, which was announced in 2010 and held up as a possible ancestor of Homo.) By ignoring those South African fossils, Berger contends, the team cannot rule out alternatives to their interpretation.

Berger also took issue with the team’s use of fragmentary material to argue its position. “All this paper does, unfortunately, is highlight the mess that the isolated and fragmentary East African record in this time period makes of the debate around the origins of the genus Homo, and it does little to illuminate the question,” he contends. Berger has previously argued that A. sediba, which is best known from two largely complete skeletons exhibiting a mosaic of australopithecine–like and Homo-like traits, demonstrates that evolution mixed and matched fossil human features in sometimes surprising ways, and that fragmentary remains therefore cannot be reliably assigned to species. “We and others have shown that you can’t take isolated bits and force them into anatomical association.  The [Koobi Fora] mandible goes with the maxilla?  Where is the evidence for that,” he demands.  “While we need more fossils like this, it’s not helpful to shoehorn them into debates they are not complete enough to be of use as evidence in.”

Spoor counters that he and his colleagues did include the South African fossils in their analysis, but that they excluded those comparisons from their report because their Nature paper focuses on the question of what the new fossils reveal about taxa of early Homo in eastern Africa. “A. africanus and sediba have nothing to say about that,” he asserts, noting that africanus and sediba have primitive faces, with “nothing specifically Homo-like in the skull.” He adds, “the interesting parts of A. sediba are in the postcranial skeleton.”

Suffice it to say, I doubt very much that we have heard the last of this debate. Stay tuned.

Update (8/9/12 at 9:53 A.M.): Paleoanthropologist Philip G. Rightmire of Harvard University sent the below observations about the new fossils. Like Van Arsdale, Rightmire has long studied the Dmanisi fossils, but he arrives at different conclusion about the Koobi Fora remains:

“It’s my impression that the authors are on the money in attributing their material to the hypodigm including KNM-ER 1470. For a long time, this group was quite poorly documented and therefore enigmatic. The new facial parts duplicate some of the key features of the original (very distinctive) face, but at a much smaller scale. Sex dimorphism and individual variation within a single lineage seems to be the best explanation. Also, it’s clear that this lineage differs from specimens such as OH 13, OH 24, and KNM-ER 1813 (attributed to Homo habilis). I’d say that there is a good case for the presence of two distinct Homo lineages along side Homo erectus. For me, an important question is which (if any) of these hominins took the first steps out of Africa, to establish settlements at localities such as Dmanisi. Our material is best described as early Homo erectus, but I think that the direct ancestors to the Dmanisi population were a more archaic form of Homo. The first hominins out of Africa may have been Homo habilis (not the group documented in the new paper). Or we may have to keep looking for an appropriate ancestor to Homo erectus. In any case, Homo erectus evolving in Asia probably dispersed only later (back) to Africa, and of course toward the Far East.”

 

Kate Wong About the Author: Kate Wong is an editor and writer at Scientific American covering paleontology, archaeology and life sciences. Follow on Twitter @katewong.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Sauce23 8:59 am 08/9/2012

    This is a terrific, and exceptionally readable, description of what is happening right now in this intriguing field.

    Link to this
  2. 2. Lowndes 10:40 am 08/9/2012

    It seems to me that this is, and will be, an ongoing discussion about our ancestry. At this point we have 167 pieces of a 10,000 piece jigsaw puzzle, and not all of our 167 pieces are in real good condition, and everyone has an opinion on what the big picture is based on these few pieces. We aren’t even sure all our pieces come from the same puzzle. This discussion is lively entertainment, listening to academics argue various points, but what we need is more puzzle pieces, if the big picture is the real goal. Seem that the big argument, rather than the big picture, is the real gold.

    Link to this
  3. 3. phalaris 11:36 am 08/9/2012

    Yes, I’m with Sauce23: this is SciAm at its best: a balanced overview of the different positions, and enough detail to make it clear what the contenders are basing their line on.
    With articles like this, even laymen can enjoy the fray!

    Link to this
  4. 4. Sauce23 12:10 pm 08/9/2012

    In science, unlike religion, one must do the best to understand things with what one has available, then adapt thinking as more pieces are added, rather than making the pieces fit preordained conclusions. I suppose we could just look at the 167 pieces and say, “huh.” That feels rather uninteresting. I disagree with Lowndes that the argument is more important than the goal. Instead, scientists disagree on the way to attaining a goal. That is how one gets to truth. Socrates knew that 2400 years ago.

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  5. 5. afn48505 2:33 pm 08/9/2012

    “The new finds—a partial face including almost all of the molars in the upper jaw, ..”
    I am confused as to why you would refer to a face and not a skull. A face to me would have flesh.

    Link to this
  6. 6. alan6302 6:15 pm 08/9/2012

    The story that modern humans were genetically engineered 200,000 years ago appeals to me. Each race was engineered separately at about the same time. This accounts for many holes in the evolution theory.

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  7. 7. TobyNSaunders 7:32 pm 08/9/2012

    It’s a shame that NYT had a story on this titled something like ‘human evolution brought into question’. It can get a bit counterproductive to have massive debates over little details; we wouldn’t want to give people the wrong idea, especially when they’re already ignorant of big picture facts about biology.

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  8. 8. Pazuzu 6:46 pm 08/10/2012

    To Alan6302: Huh?? So who did this “genetic engineering”? And why? What do you mean “race”?

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  9. 9. JRWermuth 9:03 am 08/11/2012

    It would be truly wonderful if one of these digs included the likes of Barbara Alpert Ph.D., a scholar in discerning the cultural evidence of creativity within these ancient populations. The trail of hominid evolution is fascinating but would be so enriched by the presence of pigments, configurations, or other defining material.

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  10. 10. Owl905 2:16 pm 08/11/2012

    The article was so good it was worth the re-read. ‘Rekindles’ might be an undersell after noting Berger’s reaction; his fossils might have been stepped on.

    The suggestions do indeed push ahead the multiple lineages school – a web of evolution rather than a line. The school that supports a newly-enlarged single lineage are on the defensive. They need more than just claim to make these discoveries part of one family.

    Link to this
  11. 11. Jeff English 9:14 pm 08/11/2012

    It would be extremely unlikely for there to be only one distinct lineage. Those who believe otherwise need to prove their case. It was certainly a good working assumption until more data were forthcoming. The problem of course is that we seem to have reached the limits of our ability to draw conclusions from our present data. So more data please.

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  12. 12. moberndorf 4:37 pm 08/12/2012

    I have been following this debate since I was a child, listening to my parents. I am now an archaeologist, myself, and we really don’t seem to have progressed very far in 60+ years of bickering. So many “scientists” seem to have forgotten how to keep and open mind, getting a vested interest in a “theory” that they treat as carved in bedrock. Add to this unpalatable mess the political bias that so many in Academia, and elsewhere, insist on injecting into what ideally should be pure science, and you get a proper swamp, with good material floating about among the water moccasins and the ‘gators, but damn difficult to sort out. The whole notion of “species” needs to be redefined. Amongst humans, we have tiny Asian people and Watutsis in Africa, averaging around 7′. Same species. Yet with pronghorn antelope and mule deer, a few pounds difference and a slight variation in habitat, and you have instant sub-species. With birds, just a few changes in feather color can mean entirely new species. Add “race” to the cauldron, and you have a mixture that can only curdle. On the up-side, there are still some excellent science writers capable of objectively reporting multiple facets of complex stories and making them understandable. Thanks, Kate Wong!

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  13. 13. didih 1:25 pm 08/13/2012

    Is it really unthinkable that more than one species of Homo existed in Africa at the same time? After all there exist three species of Pan in Africa today.

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  14. 14. maraven 4:45 pm 08/13/2012

    I have long been interested in this topic, and although I am an engineer by profession I enjoy reading about new findings and theories. I must say though, that I simply do not understand how archeologists determine how certain subtle variations in shape and size define a new species or subspecies. As another commenter noted, today you can look at an eskimo, a pigmy, a dutch or watusi( both notably tall) and note that all have very different skeletal characteristics. If an archeologist two million years from now were to discover these three or four separate remains what would he think, one species, three or four subspecies, local adaptations but one species. I think that rationally we need to rethink ourselves as humans, redefine the term “species” and how it is used not only in reference to us but to other living things, and also use this to shed some light on the diversity we find when we look at our ancestor´s remains. I will not go into race issues, as that will spark a never ending very irate debate. But surely there must be some way of better interpreting specific characteristics of the remains studied, their variations and that this criteria be useful to understand us Homo Sapiens as a whole, although the Sapiens bit I believe is highly overrated and self-serving.

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  15. 15. Bird/tree/dinosaur/etc. geek 11:02 am 10/22/2012

    @ alan6302: Dude, you REALLY need to check your meds. That is the single scariest comment that I have read in months.

    Link to this

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