IRA FLATOW, host:
This is SCIENCE FRIDAY from NPR. I'm Ira Flatow. Researchers reporting in the journal Nature this week say a pair of fossil bones found in Ethiopia could revise what we know about human evolution.
According to the researchers, the bones have the tell-tale marks of being cut with a tool. In other words, they were being butchered. And based on the age of the fossils, the researchers think the meat-eating occurred nearly a million years earlier than we previously thought that meat-eating actually did occur.
Other scientists are not so sure. Extraordinary claims require extraordinary evidence, to paraphrase Carl Sagan, and they are not convinced that this evidence matches the claim.
That's what we'll be talking about this hour. Our number, 1-800-989-8255. You can tweet us @scifri, @-S-C-I-F-R-I. And you can join the discussion at sciencefriday.com and also in Facebook.
Let me introduce my guests. Well, first up is Dr. David DeGusta. He is a former professor of anthropology at Stanford University. He is founder of the Paleoanthropology Institute in Oakland, California. Thanks for joining us today.
Dr. DAVID DeGUSTA (Founder, Paleoanthropology Institute): My pleasure, Ira.
FLATOW: Dr. Zeresenay Alemseged is director and curator of anthropology at the California Academy of Sciences, and he joins us from Addis Ababa in Ethiopia. Thanks for being with us today.
Dr. ZERESENAY ALEMSEGED (California Academy of Sciences): Thanks for having me, Ira.
FLATOW: You're welcome. Dr. Alemseged, you are the person who has made these claims about the bones. It sounds exciting. Tell us what you've actually found.
Dr. ALEMSEGED: Well, the claim is made by myself and by the Dikika Research Project, which is a (unintelligible) research project being conducted in Ethiopia.
What we found is the evidence for the earliest - the find, which consists of the evidence for stone-tool-inflicted cut marks dating back to 3.4 million years ago, and this pushes the earliest evidence for meat-eating and of stone tool use by one million years back.
Dr. ALEMSEGED: And the implication being that the species Australopithecus afarensis probably used tools to consume meat.
FLATOW: And the evidence are bones, you say, with evidence of cut marks from tools on them. Which kind of bones are you talking about?
Dr. ALEMSEGED: The bones are a rib bone from a large mammal, probably a big cattle-like animal, and then a small (unintelligible) femur fragment, which is probably from an antelope. And these two bones preserve evidence for cut marks, for percussion marks, which a pounding mark when you use a hammer stone to extract the bone marrow and then probably sharp-edged tools to extract meat or the flesh of the bones.
FLATOW: So pushing this age back of the first meat eater would put it about the same time as the famous Lucy skeleton?
Dr. ALEMSEGED: Yes. This takes us back to the era of Australopithecus afarensis, famously represented by the fossil Lucy, as well as the fossil Selam, which also was discovered only 200 meters away from where we found this bone.
FLATOW: Dr. DeGusta, you're not convinced yet. Why is that?
Dr. DeGUSTA: Well, first, I think before we get into the specifics, I think we should commend Dr. Alemseged and his team for the fieldwork they do at Dikika. By all accounts it's an extremely difficult place to work. So I think we all need to respect, you know, the blood, sweat and tears that they put in to recover the fossils from there, even though I strongly disagree with them, as do others, about the interpretation of these two fossil fragments.
FLATOW: What is the disagreement here?
Dr. DeGUSTA: Well, the key question is who or what made the marks, because we know that there's a variety of natural agencies, including animals, crocodiles, trampling, contact with other rocks, there's a lot of natural agencies that can make marks on the bone.
So from what has been published, I and others think it's much more likely that these marks are the result of the known ability of these natural agencies to damage bone rather than the previously unknown tool-using abilities of Australopithecus.
And I think that's certainly sort of the most parsimonious position here, because it can be difficult to determine unambiguously whether a single mark is due to an animal's tooth or to a stone tool, and they really only have two fossil fragments.
He said bones, but these are just fragments. One was about four inches by one inch, and so you can think of, if you imagine an animal the size of a cow, and you've got one fragment that's, you know, a couple inches long, that's not very much to go on to interpret how that animal was butchered or if it was butchered.
FLATOW: Dr. Alemseged, how do you answer that criticism?
Dr. ALEMSEGED: Well, I understand fully the skepticism, and actually, it reminds me of the type of skepticism that I had a year and a half ago when we made the discovery at Dikika.
But then after going through the details and then after the scanning electron microscope analysis, I was convinced because the type of agents that Dr. DeGusta mentioned are not represented in these fossils.
For example, if this agent were crocodiles, we would have found the typical fang, such as the bisected tips, the puncture marks and the furroughs.
And also, when you look into the scanning microscope images, you don't see the type of density and frequency of micro-striations, which are the very fine lines that you'd see in stone tool-inflicted cut marks.
Dr. DeGUSTA: Well, actually, crocodiles do produce those micro-striations, and...
FLATOW: Dr. DeGusta, let him finish, please.
Dr. DeGUSTA: Sure.
Dr. ALEMSEGED: So the features that we have on these bones, on these marks, are clearly indicative of stone tool-inflicted cut marks. So we have eliminated all the other agents, including the trampling, which would have included lines that would have been perpendicular to the main axis of the cut mark.
So without having eliminated this, obviously, we wouldn't have claimed that these bones were inflicted these cut marks were inflicted by stone tools.
Dr. DeGUSTA: Right, well, there's a specific point here and then a more general one. The specific one is actually (technical difficulties) on the NPR SCIENCE FRIDAY website (technical difficulties) comparison between the marks on these fragments and crocodile damage that was documented previously by Dr. Jackson Njau. And I think it's a pretty good match, but people should look for themselves.
And regardless, Dr. Alemseged and his colleague, they don't actually discuss the possibility of crocodile damage at all in their text. So to me that's a major oversight.
It also takes us to a more general question this find raises, because as Zeresenay explained, based on these two fragments, they're claiming that the early human species, Australopithecus afarensis, Lucy's species, had developed butchery using stones.
Okay, well, literally right next to their site, just a few miles away, is the famous site of Hadar, where Lucy was found, along with hundreds of other afarensis fossils and literally tens of thousands of animal fossils, same age as Dikika, same kind of early human, same place.
And yet in 40 years of research at Hadar, they've not reported a single butchered specimen, even though they have thousands more animal bones at Hadar than at Dikika.
And the same is true at all the other afarensis sites because afarensis is actually a well-known species at multiple sites, and it's not found with butchered fauna anywhere else. It kind of makes you wonder, don't it?
FLATOW: Dr. Alemseged?
Dr. ALEMSEGED: All right, let me answer. First of all, I agree with Dr. DeGusta that there was no cut marks found at the (unintelligible) Hadar site, even though there are thousands and thousands of bones.
But the discovery that we made, in a way we owe it to the new techniques that we employed at Dikika. In 2009, we started what is called 100 percent collection strategy, whereby at selected localities we collect all the bones that we have at that site.
Dr. DeGUSTA: (Unintelligible)
FLATOW: Dr. DeGusta, let him finish.
Dr. ALEMSEGED: Let me finish. As you know, the standard way of doing paleontology involves collecting fossils from the skull, from the mandible, from the teeth, and then the extremities of the long bones. Why? Because they are taxonomically valid. They are easy to identify as an animal.
We don't collect, normally, the ribs and the shafts, which we did, and if you are to expect cut marks, where do you find them? You don't find them in the head. You find them on the shaft and on the ribs, where you would expect animals to butcher, to eat or to extract meat.
So that's the point. However, looking for 40 years does not guarantee finding it. The difference between searching and discovering is that. We found it. We discovered it (unintelligible) searching.
Dr. DeGUSTA: The point (unintelligible)...
Dr. ALEMSEGED: So you can search for 40 years. It doesn't guarantee that you find them, and you find them when you find them. So that's a big I don't think that's a good argument. I think we owe it to the new technique of collecting our fossils.
FLATOW: What about, Dr. DeGusta, the new technique that he's talking about?
Dr. DeGUSTA: Well, first of all, it's not new. The Middle Awash Project, which is also right next to Dikika, has been employing 100 percent collection of selected localities since 1990, and at other places where bone modification is suspected, or you're interested in it, there's also been 100 percent collection, previously.
And in fact, as I read the Nature paper, 100 percent collection was not actually employed at the particular locality of Dikika 55 that yielded these two cut-marked fragments, because they say in the paper that the only other two bones from that locality that were collected was two pieces of giraffe.
So one of the problems that I and other have with this paper is from the specific locality where these two fragments are from, we only have two other fossils that we can compare them with. So we don't know if the other fossils from Dikika 55 are do we see carnivore chewing? Do we see crocodile damage? Do we see trampling on those other pieces? That may be very informative.
Now, it's possible that I may have misread the Nature paper, but as I read it, they actually only collected four fossils from Dikika 55...
FLATOW: Dr. Alemseged, 30 seconds to rebut here.
Dr. ALEMSEGED: Yes?
FLATOW: Go ahead, I gave you 30 seconds to answer that, Dr. Alemseged.
Dr. ALEMSEGED: Yeah, we collected all the fossils that we had at the selected localities that we identified for 100 percent collection, and again, he mentioned that the 100 percent collection was - they were collecting for 30 or 40 years. That (unintelligible) argument. Searching is different from discovering.
FLATOW: All right, that's about all the time we have for now. I want to thank Dr. Zeresenay Alemseged and Dr. David DeGusta, debating this find. If you ever thought that scientists agree with each other all the time, here's a good answer to that. Science is an ongoing problem and a solution.
Stay with us. We'll be right back after this break. Don't go away.
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