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Is Australopithecus sediba the Most Important Human Ancestor Discovery Ever?

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


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Australopithecus sediba

Composite reconstruction of Australopithecus sediba, based on remains from three individuals found at the site of Malapa in South Africa. Image: Courtesy of Lee R. Berger and the University of the Witwatersrand

Three years ago researchers added a new branch to the human family tree: Australopithecus sediba, a nearly two-million-year-old relative from South Africa. By all accounts it was a dazzling find—two partial skeletons, an adult female and young male, from a site called Malapa just outside Johannesburg. And it has been making headlines regularly since then whenever scientists release results of new studies of the material, as they did earlier this month. Any time human fossils, especially skeletons, are unearthed it’s a big deal, because such remains are so incredibly rare. But I’m going to go out on a limb here and say that A. sediba may just be the most important hominin (modern humans and their extinct relatives) discovery yet.

Now, I can already hear the protests of more than a few paleoanthropologists. But hear me out–and then if you don’t buy it you can tell me why I’m wrong in the comments.

To appreciate the importance of any given discovery, we must consider it in its historical context. Viewed that way, one might consider the 1856 discovery of Neandertal fossils in western Germany to be the most important, since it marked the beginning of human paleontology as a field of inquiry. The Taung child (Australopithecus africanus), found in South Africa in 1924, was another momentous find, offering up the first convincing evidence that humankind originated in Africa. Then there’s the 3.2-million-year-old Lucy (Australopithecus afarensis)–the most complete hominin skeleton known at the time she was found in Ethiopia in 1974 and still the best known to the public—whose anatomy established that hominins walked upright long before brain size expanded, settling a longstanding debate.  More recently, the 18,000-year-old Flores hobbit (Homo floresiensis), announced in 2004, made waves with her diminutive proportions and other traits that challenge longstanding ideas about hominin adaptation and biogeography. And Ardi (Ardipithecus ramidus) was a sensation when scientists unveiled her in 2009, suggesting that some enduring notions about the origin of bipedalism and the last common ancestor of humans and chimpanzees might be wrong.

These fossils and many others are landmark discoveries in paleoanthropology, finds that have filled crucial gaps in scientists’ understanding of human origins. They are all vitally important. And yet the A. sediba fossils manage to stand out from even this elite crowd, because of the sheer volume and quality of information they contain. The finds from Malapa tick pretty much all the boxes on a paleoanthropologist’s wish list. Specimens that preserve multiple skeletal elements? Check. Remains of multiple, coeval individuals (important for understanding variation within a species)? Check. Fossils in near-pristine condition, thus eliminating uncertainties about how pieces fit together? Geological context that allows for precision dating of the fossils? Associated plant and animals remains? Check, check, check.

Since the initial announcement in 2010 the discovery team, led by Lee Berger of the University of the Witwatersrand in Johnannesburg, has published a slew of papers detailing what A. sediba looked like, when it lived, what it ate and how it is related to us, among other insights. The latest analyses, described in six papers published in the April 12 Science, reveal a creature that excelled at climbing trees and also walked upright on the ground with its shoulders shrugged and its arms unswinging, rolling its feet inward with each step—a previously unknown form of bipedalism. Yet in contrast to its alien way of walking, aspects of A. sediba’s teeth and jaws are decidedly familiar, resembling those of our genus, Homo, according to two of the new studies. Indeed A. sediba’s dizzying mosaic of apelike and humanlike traits is a theme the researchers have emphasized with each new round of papers. And it is this mosaic that has researchers debating the central question about the hominins from Malapa: namely, where they belong in our family tree.

Berger and his colleagues have argued from the beginning that A. sediba might well be the long-sought species that gave rise to our genus (or a close relative of that species). Such an arrangement would root Homo in South Africa instead of East Africa and could banish Lucy’s species–traditionally thought to be in our direct line of ancestry—to the evolutionary sidelines. But critics have countered that A. sediba is not particularly Homolike overall and that it probably instead belonged to a South African lineage of hominins that ultimately went extinct—one of many dead-end branches in our family tree.

Because the origin of Homo is perhaps the biggest mystery in paleoanthropology, A. sediba’s perceived importance would get a big boost if new evidence were to strengthen its link to Homo. But I’d go one step farther and argue that regardless of whether it is found to be the ancestor of Homo or a dead-end branch of humanity, the Malapa hominins are now the ones to beat. Because what A. sediba brings to the table is the potential for the most detailed understanding yet of a hominin anywhere near this old.

The Malapa site is an incredibly high-resolution time capsule. The hominin remains include bones that rarely, if ever, turn up at early hominin sites, and bones often preserved only as fragments have survived intact here. Moreover, the hominins represent a range of developmental stages: in addition to the two skeletons, the site has yielded more fragmentary remains of another 4 individuals, including an infant, which will allow the team to study maturation in the species.  And the fossilized plants and animals at Malapa are the actual plants and animals the hominins had in their environment, not aggregations of remains over a period of thousands or tens or even hundreds of thousands of years.

Furthermore, conditions at the site, which was once a 30- to 50-meter-deep underground cavern with a shallow freshwater pool at the bottom, apparently allowed for the preservation of some very unusual features. The teeth of the young male were found to have tartar on them, which the research team was able to analyze for clues to what he ate in his final days. Previously the oldest known hominin tartar came from much younger Neandertals and early modern humans. And at the annual meeting of the Paleoanthropology Society in Honolulu earlier this month, Rachelle Keeling of the University of the Witwatersrand reported that molecular imaging of what appears to be skin preserved on some of the bones supports that interpretation. If verified this would be the first evidence of fossil hominin soft tissue, and could conceivably provide insights into A. sediba’s skin color and hair color, and the distribution of hair and sweat glands. Such skin features are themselves clues to the body’s ability to offload excess heat, which became increasingly important as hominins became more active over the course of evolution.

OK, I’m more than 1,000 words into this post and I’ve still barely scratched the surface of what makes the A. sediba find so extraordinary. I can’t hope to be comprehensive here, but I do want to mention two more aspects of this discovery that add to its importance. First, there are more fossils to come, perhaps lots more. CT scanning of some of the many chunks of rock blasted from the site by limestone miners back in the early 1900s has already revealed several bones. And additional hominin bones can be seen sticking out of the ground at Malapa, awaiting excavation. (This blew my mind when I visited the site in November of 2011.)

Second—and this may sound a little insidery, but it’s critical–the way Berger and his collaborators are studying the finds and disseminating what they learn represents a real departure from the cloak-and-dagger manner in which paleoanthropological investigations often proceed. Berger has assembled a huge team of specialists to work on the remains and has made the project open access, with a policy of granting permission to any paleoanthropologist who asks to see the original fossils. He has also sent out scores of replicas to institutions around the world, and routinely brings casts of the bones—even ones that his team has yet to formally describe–to professional meetings to share with other researchers. This can only improve the quality of the science that comes out of the project and may well inspire other teams to be more forthcoming with their own data.

So there you have it. That’s my case. I realize the importance of a fossil depends on the question one is asking of it—e.g. if you want to know about the origin of, say, art, A. sediba is irrelevant. And yes, at the end of the day we need loads of fossils (and artifacts and DNA) from different times and places to piece together the full story of our origins. I’m just awed and delighted by the opportunity this discovery affords to see a human species from so very long ago in such vivid detail—whether it is the elusive ancestor of Homo, or a creature from a parallel lineage that reveals another way of being human and could perhaps elucidate why our line succeeded where others failed.

Think another hominin discovery is more important than this one? I’d love to hear which one and why in the comments. Maybe you’ll change my mind.

 

 

 

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. syzygyygyzys 4:50 pm 04/24/2013

    Very interesting. Please provide more on this subject as your time permits.

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  2. 2. way2ec 2:52 am 04/25/2013

    I’d like to side step the qualifier “most important”, much like being asked what color is “most important” or even “What’s your favorite color?” On the other hand you’ve done a wonderful job impressing me with the wealth of information forthcoming from this discovery, or series of discoveries. Thank you for highlighting Berger’s professionalism, his openness may prove to be as rewarding as his findings. Thank you for sharing your enthusiasm. May I join you in stating that this hominin discovery is absolutely one of the most important discoveries yet made?

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  3. 3. jtdwyer 2:56 am 04/25/2013

    I’m just a pedestrian bystander, but making the discoveries openly available to all researchers could certainly have a profound effect on forthcoming results!

    One point, it seems to me that the excellent preservation condition of the fossils at this site may be more relevant to this discovery than it appears: how many other A. sediba lived in perhaps other areas that haven’t been found because local conditions did not support preservation? Can a population’s range be presumed from one site that, at least for some time, provided ideal conditions for preservation? Perhaps if conditions at the site had been so favorable at other times, fossils of other hominids would be found there…

    Lastly, as a casual observer, doesn’t the general structure of this skeleton more closely resemble Neanderthals than modern humans? I realize that this seems to be the wrong direction to find a Neanderthal progenitor, but we can’t really be sure of the range of A. sediba or the range of Neanderthal progenitors, can we?

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  4. 4. Carlyle 4:52 am 04/25/2013

    Nothing to contribute except to express my thanks & to echo the commenters above. Both to Kate Wong for bringing this information to us & to the research team lead by Lee Berger. Particularly I am delighted by the open access policy.
    We can dream of the day when this is the rule rather than the exception.

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  5. 5. N a g n o s t i c 10:16 am 04/25/2013

    Does the current state of mitochondrial population genetics square with the southern Africa origin proposal?

    Also, as another pedestrian bystander I’ll respond to jtdwyer: Sebida is an australopithecine type, and predates genus Homo substantially.

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  6. 6. kwong 11:23 am 04/25/2013

    @syzygyygyzys If you check out the links embedded in the article, you’ll find much more info on A. sediba from me and others

    @way2ec: Thank you and yes!

    @jtdwyer: A single site cannot tell you much about a population’s range. A. sediba is new to science so it remains to be seen whether researchers find it elsewhere. But even if they don’t, absence of evidence is not evidence of absence, as the saying goes. I don’t think there’s anything to link A. sediba to Neandertals in particular.

    @Carlyle: Thanks for the kind words!

    @N a g n o s t i c: I don’t know that mtDNA population genetics say anything about the origin of Homo–origin of H. sapiens, yes, but not earliest Homo.

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  7. 7. jtdwyer 11:32 am 04/25/2013

    N a g n o s t i c,
    That’s the heart of the matter, regardless of its current classification: please see http://www.nature.com/news/2011/110908/full/news.2011.527.html
    “That is exactly what you’d expect when you find a very transitional form: 50% of the field saying they’re right, it’s an Australopithecine, the other half saying, put this in the genus Homo…
    “At around 420 cubic centimetres, A. sediba’s puny brain compares to those of other Australopithecus specimens and chimpanzees. But a high-resolution synchrotron scan of the brain’s impression on the skull shows enlarged frontal areas that are normally associated with humans and linked to higher cognitive abilities, such as planning.”

    Many other features, including teeth, hands, pelvis and ankles offer conflicting indications… I’m just suggesting that the mix of features seem to better match Neanderthals’ characteristics than modern humans’.

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  8. 8. N a g n o s t i c 12:12 pm 04/25/2013

    jtdwyer and kwong, I suppose it’s safe to say it’s a toss-up until more evidence is found.

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  9. 9. Torbjörn Larsson, OM 1:54 pm 04/25/2013

    Terrific article!

    But as way2ec I’ll have to punt on “the most important”, since it is so context dependent. Some of the most informative perhaps, but Dmanisi seems to challenge it for social context and more. (But I’m no anthropologist, astrobiology interest here.)

    Speaking of which, Berger seems to be a great value adder, compare with H. floresiensis and its early troubles.

    “I’m just awed and delighted”.

    I’m just jawed and enlightened. [/sets jaw and places tongue firmly in cheek]

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  10. 10. Torbjörn Larsson, OM 2:13 pm 04/25/2013

    @jtdwyer: “Lastly, as a casual observer, doesn’t the general structure of this skeleton more closely resemble Neanderthals than modern humans?”

    As a casual observer I note that Au. sediba is dated to way before the ancestor to Moderns, Neanderthals and Denisovans, namely H. erectus. It even predates what now looks like the odd man out, H. habilis.

    Not that I am a specialist, but there seems to be just one Homo-homologous curved jaw dated to before that (@ 2.33 Ma bp). But I also heard somewhere that its dating is controversial (don’t quote me on that!), and mostly this again mosaic species confirms that looking at an isolated trait means exactly zip.

    In any case, since there was a long lived Homo species before the later diversification, it would be hard to see if it clusters more closely with one of the (to date, with hints of more concurrent subspecies in Africa) removed three descendants at any level of significance.

    As I understand it the origin of Neanderthals is out, but that the anthropologists still prefer a European origin. [ http://en.wikipedia.org/wiki/Neanderthal#Origin ] Everything else alike, Neanderthals and Denisovans should be the least similar to sediba – temperate Europe/Asia and subtropical south Africa are very different environments.

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  11. 11. Torbjörn Larsson, OM 2:14 pm 04/25/2013

    Oops, I meant “causal observer. The joke’s on me!

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  12. 12. Torbjörn Larsson, OM 2:38 pm 04/25/2013

    More corrections: it wasn’t the jaw, it was the upper part of the mouth (“maxilla”). I remembered that even before I started to check, which lead me – back to the article’s links. [ http://blogs.scientificamerican.com/primate-diaries/2013/04/17/the-mosaic-of-human-origins/ ] It _is_ a good article. And it appears you _can_ quote me on dubious dating.

    The thing is, I learned last week there are three fossils that are used to try to test (reject) sediba as ancestral to Homo. One is a jaw, which has a really iffy dating if I understand correctly, and a small part of a scull that has a really iffy classification (and again, a single trait, here skull curvature, doesn’t seem to mean much now). And then this maxilla. I’m trying to keep all three parts in my skull. =D

    (Even if finds slightly predate the current sediba finds, you can’t really tell ancestry that way as I understand it, seeing how populations can overlap in time, and how the finds _don’t_ overlap in locale. So it looks like a kind of silly fossil war to an outsider.)

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  13. 13. syzygyygyzys 5:11 pm 04/25/2013

    Yes, I found the links. Can’t wait for more.

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  14. 14. alan6302 6:24 pm 04/25/2013

    Just to irritate, I will go with Edgar Cayce’s Atlantis origin. His story could also be interpreted as a replacement for humans. That would irritate everyone.

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  15. 15. David Marjanović 5:46 am 04/29/2013

    And it is this mosaic that has researchers debating the central question about the hominins from Malapa: namely, where they belong in our family tree.

    And yet, none of them has conducted a phylogenetic analysis. An analysis would give them a most parsimonious tree they could, at the very least, start from; but they’re not doing it. What is it with paleoanthropologists?

    doesn’t the general structure of this skeleton more closely resemble Neanderthals than modern humans?

    Only in the lack of a few of our innovations. We and the Neandertalers are much more closely related to each other, sharing a common ancestor just 600,000 years ago, than to A. sediba.

    Does the current state of mitochondrial population genetics square with the southern Africa origin proposal?

    It can’t say anything about that; there are no data between us, Neandertalers and Denisovans on the one hand and chimps + bonobos on the other.

    More corrections: it wasn’t the jaw, it was the upper part of the mouth (“maxilla”).

    The maxilla forms most of the upper jaw. (Or even all of it; I think human-anatomists call the fusion product of maxilla and premaxilla simply “maxilla”. The premax, one on each side like the maxilla, carries the upper incisors.)

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  16. 16. syzygyygyzys 7:05 am 04/29/2013

    Whoa! Bonobos can spell parsimonious!

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  17. 17. David Marjanović 8:18 am 04/29/2013

    Please explain.

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  18. 18. profleeberger 1:23 am 05/8/2013

    @David Marjanovic just FYI, we have in fact run a phylogenetic analysis. You can see the resulting cladogram on page 10 of the Supplementary Online Material of the original description of sediba in Science. Its free to download here http://www.sciencemag.org/content/328/5975/195.abstract

    In brief though, the most parsimonious cladogram produced from the characters analyzed place sediba at the root of the Homo clade. We could not, however, use postcranial characters in this analysis as there really are none for early Homo other than Homo erectus.

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  19. 19. kaikamul 4:51 pm 11/21/2013

    I’m a finnish archaeology student doing my master thesis right now about the matter. And I would just like to say, that despite the fact that i’m not able to see the actual fossils, I’m really exited about them. It feels like I know them already by heart.

    kwong might be right about them being “the most important fossil”, but I’m not going to take part into that conversation.

    I found in my studies, that actually Lee Berger and Raymond Dart have great many things in common, both in their career and in fossils they found. And by that I mean the reaction, that both findings, the Taung Child and Malapa Hominin got. And, to me, it is inspiring that by being sure of what you have found you have strength to carry on despite of opposition.

    I’m certain, that at least to Prof. Berger Australopithecus sediba IS the most important discovery ever. And for me it is, too.

    Link to this

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