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The Earliest Homo

April 23, 2015

People are usually curious about their ancestors. I was told a few stories about my grandparents, and my wife was told an impressive number of stories about her distant relatives. My grandparents were born at about the time that Heinrich Hertz demonstrated the existence of radio, and decades before the Wright brothers demonstrated human flight.

Unless you're from some renowned family, the trail of your ancestors is usually gone after just three, or four, generations. After that, our history is dissolved into the life stories of the many people who have lived before us. We can somewhat relate to the life stories of people in ancient texts, such as the Old Testament. According to James Ussher, such tales go back as far as about six millennia from the present.

With advances in methods of radiometric dating and paleoanthropology, we have a good idea of how far back we can claim our existence as a species, Homo sapiens. We are just one species of the genus, Homo, that includes such memorable characters as Homo erectus, who lived as early as 1.9 million years ago; Homo habilis, who lived as early as 2.8 million years ago; and, Homo neanderthalensis, who lived as early as 350,000 years ago.

Homo heidelbergensis.jpg

I think his music was popular in the 1990s.

This is an artistic rendering of the appearance of a male of the species, Homo heidelbergensis, which dates back at least 600,000 years.

Neanderthals and modern humans are descendants of Homo heidelbergensis, with Homo sapiens appearing about 130,000 years ago.

Photograph by Jose Luis Martinez Alvarez, via Wikimedia Commons.)

Paleoanthropologists are still digging up evidence (pun intended) of man's early origins; and, just as in much of science, luck plays a large part in their discoveries. This was the case for the recent find of an ancient Homo mandible in the Afar region of Ethiopia.[1-5] This mandible, which is the the lower jaw holding the lower teeth, was dated to be 2.8 - 2.75 million years old. This date is 400,000 years earlier than that of other fossils of the Homo lineage.[5] Discovered with this mandible were other fossils between 2.84 and 2.58 million years old that aid in a reconstruction of this Homo's environment.[2]

This fossil, designated the LD 350-1 Homo mandible, was discovered and analyzed by a huge international team from the University of Nevada Las Vegas (Las Vegas, Nevada), Arizona State University (Tempe, Arizona), Pennsylvania State University (University Park, Pennsylvania), George Washington University (Washington, DC), University College London (London, UK), the Authority for Research and Conservation of Cultural Heritage (Addis Ababa, Ethiopia), CNRS Géosciences Rennes (Rennes, France), the Berkeley Geochronology Center (Berkeley, California), the Leibniz Institute for Evolution and Biodiversity Science (Berlin, Germany), the Richard Stockton College of New Jersey (Galloway, New Jersey), the University of California (Berkeley, California), and the Swedish Museum of Natural History (Stockholm, Sweden).

Lee Adoyta region of Ethiopia

Photograph of the area of the Afar Regional State of Ethiopia in which the fossil Homo mandible was found.

(Pennsylvania State University photo by Erin DiMaggio.)

The mandible was found in the Ledi-Geraru area of Ethiopia where faults have exposed layers of fossil-bearing sedimentary rock.[4] This research project was started in 2002 to examine the same area where the "Lucy" fossil was found.[5] Lucy was a more apelike creature of the species, Australopithecus afarensis, that lived 3.2 million years ago. Thirteen years into the project, team member and Arizona State University graduate student, Chalachew Seyoum, found the fossil.[5] Says Seyoum,
"I had good experience in field surveying and knew where potential sediments are. I climbed up a little plateau and found this specimen right on the edge of the hill."[5]

Chalachew Seyoum

Chalachew Seyoum, the Arizona State University graduate student who discovered the Homo mandible.

(Still image from an Arizona State University video.)

Since it wasn't possible to date the fossil mandible directly, dating was established by radiometric analysis of volcanic ash layers above and below the specimen. The argon-40/argon-39 method determines the age of the volcanic ash through the isotope ratios.[4] Says Erin DiMaggio, lead author of one paper on this study and a research associate in the Penn State Department of Geosciences, "We used multiple dating methods including radiometric analysis of volcanic ash layers, and all show that the hominin fossil is 2.8 to 2.75 million years old."[4]

This find connects a lineage between Lucy, a member of the more apelike Australopithecus afarensis, and Homo fossils dated to 2.3 million years and younger.[5] The mandible has both primitive and more modern traits, including advanced features such as slim molars, symmetrical premolars and an evenly proportioned jaw. However, it does have the primitive, sloping chin present on Australopithecus afarensis.[1,3,5] It's thought that the creature associated with the mandible walked on two legs, and research is still in progress to determine whether it would have used stone tools.[5]

2.8 Mya Homo mandible

2.8 Mya Homo mandible photographed near its discovery site.

(Arizona State University photo by Brian Villmoare.)

Examination of other vertebrate fossils of the same period indicates a habitat of mixed grasslands and shrub lands with forested areas and trees lining rivers or wetlands.[2] Fossils found in the area include prehistoric antelope and elephant, a type of hippopotamus, crocodile and fish.[4] The environment was probably like that of the Serengeti Plains or the Kalahari, and it's thought that global climate change at the time resulted in evolutionary changes in many mammals, including hominin.[4]

The Ledi-Geraru Research Project is funded by the National Science Foundation, the American Association of Petroleum Geologists, the Society for Sedimentary Geology, and the Geological Society of America, among others. [4-5]


  1. Brian Villmoare, William H. Kimbel, Chalachew Seyoum, Christopher J. Campisano, Erin DiMaggio, John Rowan, David R. Braun, J. Ramon Arrowsmith, and Kaye E. Reed, "Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia," Science, Advanced Online Publication, March 4 2015, DOI: 10.1126/science.aaa1343.
  2. Erin N. DiMaggio, Christopher J. Campisano, John Rowan, Guillaume Dupont-Nivet, Alan L. Deino, Faysal Bibi, Margaret E. Lewis, Antoine Souron, Lars Werdelin, Kaye E. Reed2, and J. Ramón Arrowsmith, "Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia," Science, Advanced Online Publication, March 4 2015, 10.1126/science.aaa1415.
  3. Ann Gibbons, "Deep roots for the genus Homo," Science, vol. 347, no. 6226 (March 6, 2015), pp. 1056-1057, DOI: 10.1126/science.347.6226.1056-b.
  4. A'ndrea Elyse Messer, "Earliest known fossil of the genus Homo dates to 2.8 to 2.75 million years ago," Pennsylvania State University Press Release, March 4, 2015.
  5. Discovery of jaw by ASU team sheds light on early human ancestor, Arizona State University Press Release, March 4, 2015.

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