ASU Human Fossil Discovery

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The earliest known fossil of the human genus was discovered by a team from Arizona State University in Ethiopia in 2013. The lower jaw with five teeth is dated to 2.8 million years ago, setting back the first known example of the human genus 400,000 years. William Kimbel, director of ASU’s Institute of Human Origins, and ASU anthropology graduate student Chalachew Seyoum, who discovered the fossil, will discuss the extraordinary find.

Simons: Coming up next on "Arizona Horizon," an extraordinary fossil find that may change the timeline of human development. And we'll hear about a new recording by the Phoenix Chorale. Those stories next on "Arizona Horizon."

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Ted Simons: Good evening and welcome to "Arizona Horizon." I'm Ted Simons. Arizona's seasonally adjusted jobless rate for January remained at 6.6%. The state department of administration says Arizona lost 43,000 jobs in the first month of the year as employers let people go following the holidays. Eight of Arizona's 11 employment sectors lost jobs in January gained sectors gained jobs and one remained flat. The earliest known fossil of the human genus was recently discovered by an ASU team in Ethiopia. The fossil consists of a lower jaw with five teeth and it dates back 2.8 million years. For more on the discovery, we welcome William Kimbel, director of ASU's Institute of Human Origins, and Chalachew Seyoum, an ASU graduate student from Ethiopia who actually found the fossil. Good to have you both here. Thank you so much for joining us.

Chalachew Seyoum: Thank you for having us.

Ted Simons: What actually was discovered and where?

William Kimbel: The fossil discovery, our team made, is that of a lower jaw of a human ancestor containing about half a dozen teeth and it dates to about 2.8 million years ago, recovered from a very rich place called lady gararu in the northern part of the Ethiopian rift valley. And this is an area where teams have been searching for many years and have made a number of remarkable discoveries and this is the latest among them.

Ted Simons: Why are discoveries made there? Why was this targeted and not down the street somewhere?

William Kimbel: The Ethiopian rift valley is one of the richest sources of human fossils in the world bearing on the very earliest emergence of humans. Ethiopia, Kenya, Tanzania, many east African countries have contributed important finds because these ancient sediments are actually exposed at the service today and erosion brings these bones out onto the modern service for us to find.

Ted Simons: And you found this jaw with five or six teeth. First of all, tell us what you were looking for when you found this.

Chalachew Seyoum: Yeah, that morning we were surveying the locality and I just walked to one of the hills. It's sediment and I was looking for fossils, actually we were looking for potential hominids by that morning, and one of the tooth was popping out from the sediment and just caught my eye. I was walking and I sat down and looked at it very closely and it was a tooth. So when I picked it up, it's a mandible, a piece of mandible.

Ted Simons: When you picked it up, did you think this might be older than 3 million or younger than 2 million? Did you realize exactly what you got?

Chalachew Seyoum: The first thing I knew was it was a hominid. Ancient human jaw. And we know we were targeting a particular time period between 2.5 and 2.8 million years old so we know it's not older than 2.8 million and it would be between 2.8 and 2.5 million years old. We know where we were looking.

Ted Simons: Okay. And again, there's that jawbone, there are the teeth, the idea you were looking for something between 2.5, 2.8, talk to us about Lucy, which is 3 million and why it's so important you found this.

William Kimbel: The African fossil record gives very powerful testimony to our emergence from an ape-like ancestor. We see first with the emergence of two-legged walking, bipedalism by four and a half million years. By 3 million years ago, we see that perfected in Lucy, for example, also a creature. And by 2 million or so we see the emergence of larger brains and sophisticated stone tool technology coming into the record. So a very nice fossil record but it's not complete and one of the gaps that we've been confronted with is the period between two and a half and 3 million which bits of fossil evidence has indicated would be the time when our lineage, our genus, homo, would have emerged. Because that's a particularly poorly represented area, any fossil is bound to have a major impact and this jaw dated does exactly that.

Ted Simons: You were looking for this but how do you know that that area would have something in this 500,000 to 700,000 some odd year how do you know to look there?

Chalachew Seyoum: This has a number of disciplines. So we have geologists, archeologists, paleontologists, so the geologists dated that sediment and they already gave us this estimated edge of that particular site. So the geologists know, you know, the date. So we know the time period.

Ted Simons: And there you are. Again, when you saw this, you look happy there but did you really know exactly what you had. This transitional kind of fossil.

Chalachew Seyoum: I knew. You can see from my smile. And I was very excited, you know, because like every scientist, when they go out for fields, they have questions, they have hypotheses. The question was to find a hominid from that time period. I know it was going to be very important given the time period so I was very excited.

Ted Simons: What were your thoughts when this was discovered?

William Kimbel: Well, I saw it a little while later. The national museum of Ethiopia where it's curated and one of the things that struck me was how different it was from the ancestral Lucy type of human ancestor.

Ted Simons: Real quickly, why is it different?

William Kimbel: We can see in the shape of the teeth, and in the architecture of the jaw itself, the fossil record shows the emergence of a modern human form over millions of years. And it moves from ape like or more primitive to more advanced, more human-like. And this jaw sits at a time period, 2.8 million, shows very early traces of the emergence of human-like characteristics in the jaw and teeth, the shape and architecture of this part of the skull. What is driving these changes? Well, sensibly we would think there's something about the diet that is probably changing in human evolution between a Lucy-like creature and our own lineage. What those changes were in detail we don't know yet but that's the subject of continued thinking and analysis but it most likely had something to do with what these creatures were eating.

Ted Simons: Interesting. Now, you are Ethiopian, correct?

Chalachew Seyoum: Yes.

Ted Simons: And this was discovered in Ethiopia. Had to be pretty exciting for you.

Chalachew Seyoum: It was very exciting, for a number of reasons. So this will confirm that Ethiopia and other east African countries are the place where human beings began. And this is especially this jaw which belongs to the genus which we are also is the beginning of the human being. It's very interesting. And it's very good for Ethiopia to be represented by this jaw in addition to the previous discoveries.

Ted Simons: So again, what did we learn from this discovery?

William Kimbel: Discoveries in this particular period of geological time between 2.5 and 3 have been very poor in quality and few in number. What this helps us do is it helps us link the ancestral line of Lucy to us by providing a link if you want, we don't like the term missing link but a link in time between an ancestor and a descendant, us. It helps narrow the window in which our team and other teams working in Ethiopia and elsewhere in east Africa should begin to look for even earlier traces of our lineage that will help firmly tie back to something like Lucy.

Ted Simons: And my last question for you is that's what we learned. What questions are raised?

William Kimbel: This is the question we always ask us. What are the next questions? We want to know what is driving the changes in the jaws and teeth. So diet as I mentioned before is one area where we need to start thinking about questions that would have been responsible for the deviation of our line from that of Lucy in terms of dietary behavior. We usually associate the genus homo to which our own species belongs again with big brains and sophisticated culture, technology, but we don't know as we sit here whether those changes emerged at the same time as the changes in the teeth and jaws. Don't have that record yet. So we'll be looking as other teams will in this now narrowed period of time for any clues as to the emergence of other human characteristics that we see in ourselves as unique.

Ted Simons: Well, congratulations to both of you, great find out there, by the way. Good work on your part. Congratulations to both of you and continued success.

William Kimbel: Thanks so much.

William Kimbel:Director, Institute of Human Origins at Arizona State University; Chalachew Seyoum:Anthropology Graduate Student, Arizona State University;

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