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Press backgrounder: First homo sapiens

Immediate predecessor of modern humans found in Africa; 160,000 year old Ethiopian fossils are first homo sapiens

(The official date of publication in the journal Nature is June 12, 2003)

Media contact info, images, and video:
  NOTE: To set up an interview with Tim White, e-mail him at timwhite@socrates.berkeley.edu. He will respond promptly to reporters on deadline. His phone, (510) 642-2889, has no answering machine.

Image downloads• IMAGES: Call photographer David Brill to obtain photos: (770) 461-5488 or brill@mindspring.com.

• VIDEO: An 11-minute video taken in the field and in the National Museum of Ethiopia shows the skulls, their excavation and reconstruction, and includes interviews with Berhane Asfaw and Yonas Beyene. The video can be previewed online. Broadcast-quality Beta dubs can be obtained by calling Media Relations at UC Berkeley: (510) 642-3734.

- Scientists working in Ethiopia's Afar Regional State have recovered the fossilized crania of two adults and a child. These African fossils are now the world's oldest near-modern humans. The remains bear cut marks made by stone tools and thereby demonstrate a form of early mortuary practice. The discoveries appear as a cover story in the June 12th issue of the journal Nature.

The Discovery and Preparation

• The fossils were found in the Middle Awash study area of Ethiopia, in the Afar depression. The site is located at Herto village on the Bouri peninsula, about 140mi (230km) northeast of Addis Ababa, Ethiopia's capital.

• Herto Locality 16 was discovered on November 16, 1997 when Tim White, one of the project's leaders, spotted a butchered fossil hippopotamus skull and associated stone artifacts eroding from sandy sediments immediately east of Herto village. The first hominid fossils were found when the team returned to survey the site eleven days later, just before lunch.

• The most complete of the new hominid fossils is an adult male cranium (skull lacking lower jaw) with heavily worn teeth, found embedded in ancient cemented sands by Berkeley doctoral candidate David DeGusta. The first evidence of mortuary practice was identified on skullcap pieces representing a second adult individual, this one found nearby by Cesur Pehlevan, a Turkish paleontologist working with the research group. He spotted scattered pieces of an adult skullcap atop an archaeological site with stone tools and butchered hippopotamus bones. Dr. Berhane Asfaw of Addis Ababa found the third major individual, a child's shattered cranium, six days later at the same locality.

• Working during field seasons between teaching and administrative schedules, it took the team's paleontologists three years to clean and restore the fossils before they could be compared and analyzed. During this period the archaeologists were busy excavating and analyzing nearby artifacts. At the same time, geologists and geochronologists worked to establish the age of the finds.

• Over 200 pieces of the child's cranium were recovered from a large area of scatter (>400 square meters). As this fossil emerged from the sediments in which it was embedded, it shattered into small pieces that were subsequently dispersed by trampling livestock, frequent whirlwinds, and occasional downpours. Dr. Asfaw, removed the rock-hard sandstone cemented to each of the small pieces. Using tiny anatomical clues, like the impressions of individual blood vessels, he repositioned each fragment of bone and glued the specimen together. "It was an anatomical puzzle in three dimensions. I was able to use modern human skulls as the key to put the child's cranium back together again." Asfaw said.

• The adult cranium was found in situ (in place), still embedded in the sediments. For safe extraction and transport over dry river gullies and unpaved tracks between the field site and the laboratory in Addis Ababa, a protecting and a reinforcing "jacket" of plaster was formed around the specimen before it was removed. Safely delivered to the National Museum of Ethiopia, the fossil was further painstakingly excavated from the embedding sand and sandstone by the researchers during a two-year process. Using microscopes, and dental and other fine instruments, they removed matrix from the fossil one grain at a time. Each newly exposed surface of the soft bone was immediately saturated with a hardening preservative as they worked. This precise mode of extraction requires great skill and patience to avoiding any further damage to the fossil.

The Fossils

• Found were the crania of two adults and a child. Additional skull pieces and isolated teeth from 7 other individuals were also found.

• All of the fossil hominids are of the same species, and were found within 200 meters of one another. All had eroded from the same geological layer of ancient river and beach deposits.

• Stone artifacts and modified bones are abundant in this layer, but there is no way to know the exact relationships among the three hominid individuals. There was no evidence of intentional burial of the crania, and no other bones of the skeleton were found on the surface of the locality, or in excavations conducted after the initial discoveries.

The Environment

• Today the Bouri area is inhabited by the Afar people who are semi-nomadic pastoralists living in this harsh environment. Herto is one of their villages on the floor of the Afar rift valley. It had been temporarily abandoned when the new fossils were found in 1997.

• Project geologists and paleontologists have established that the 160,000 year-old Herto hominids lived near the shore of a shallow freshwater lake inhabited by abundant catfish, crocodiles, and hippos. While this was occurring at Herto, much of Europe was buried in ice during a major glaciation.

• According to project geologist and co-leader Dr. Giday WoldeGabriel of Los Alamos National Laboratory in New Mexico, major faulting uplifted the Bouri peninsula, thereby blocking the ancestral Awash River: "This created a paleo-lake that attracted the animals whose fossilized bones we now find eroding from the Pleistocene sediments alongside the remains of the hominids."

The Culture

• The stone tools of Herto were studied by the legendary Berkeley prehistorian J. Desmond Clark before his death last year. His colleagues Dr. Yonas Beyene of Ethiopia's Authority for Research and Conservation of the Cultural Heritage, and Dr. Alban Defleur of Marseilles, France, joined in this work. Dr. Jean-Renauld Boisserie (University of Poitiers, France) studied the butchered hippopotamus remains.

• Stone tools found with the hominid fossils document a transitional phase in stone tool technology wherein earlier handaxe-dominated assemblages of the Acheulean gave way to later flake-dominated assemblages of the Middle Stone Age. Dr. Yonas Beyene, the team's archaeologist, says that the stone tools are important: "The associated fossil bones show clearly that the Herto people had a taste for hippos, but we can't tell whether they were killing them or scavenging them. These artifacts are clues about the ancestors who made them." In the hominid discovery horizon, a hippo cranium with a deep chop mark made by a stone tool was found.

Mortuary Practice at Herto

The more fragmentary adult cranium from Herto shows parallel incisions around the perimeter of the skull. These superficial cut marks were made by a stone tool that was repeatedly drawn across the skull's surface. These marks differ in placement and orientation from those that made by defleshing with stone tools. They reveal some form of ancient mortuary practice. The child's cranium is even more intriguing in this regard. Here, cutmarks made by a very sharp stone flake were found deep in nooks and crannies of the skull's base. The rear part of the cranial base was broken away, and the broken edges polished. The sides of the skull show a deep polish that may have formed from repeated handling of the skull after it was defleshed.

Anthropologists have found similar bone modifications in societies where the skulls of ancestors are curated (preserved) and worshipped. This pattern of modification to the Herto crania appears to constitute evidence of organized and prolonged mortuary ritual, whereas the 600,000-year-old Bodo skull (also from the Middle Awash) displays cutmarks associated with tissue removal, but no evidence of polishing.

It is clear that the modifications on the Herto crania were made by other hominids when the bone was fresh (before fossilization). However, according to the scientists it is impossible to establish whether the flesh or brains of the deceased were consumed as part of a cannibalistic ritual. Similarly modified skulls were collected among tribespeople of New Guinea during the last century.

Herto and Human Evolution

• The Herto fossils represent a fiber in the evolutionary twine connecting modern humans and our earlier ancestors. According to Tim White, "Now we have a great sequence of fossils showing that we evolved in Africa, and not all over the globe." Species in this evolutionary sequence include Homo erectus, now well known from earlier and later representatives such as the Turkana Boy skeleton, from Kenya (1.7 myr) and the Daka cranium from the Middle Awash (1.0 myr). A younger (600,000-year-old) cranium from Bodo, also in the Middle Awash, links those early fossils and later ones, including these Herto discoveries.

• The anatomy of the Herto crania was studied intensively using a variety of comparative anatomical methods. Multivariate statistics were used to compare dimensions of the adult male cranium to other fossils, as well as to a worldwide sample of several thousand modern human skulls. The team found that the Herto adult male cranium could not be matched for its robusticity or length among the 3,000 modern human skulls used for comparison.

• The new Herto fossils approximate--but do not duplicate--the anatomy of modern humans. For instance, the deep face and long, rugged braincase lie just at the edge of the modern human range. The Herto crania are therefore anatomically near-modern. The adult cranium has a cranial capacity of approximately 1450 cubic centimeters, slightly above the modern human average of between 1350 and 1400cc.

• The Herto fossils are similar to modern human crania in key characters of the face and cranial vault, but there are a few differences. Because they are so close to modern humans in shape and size, the scientists placed them in Homo sapiens, but in their own subspecies Homo sapiens idàltu ("idàltu" means "elder" in the Afar language). The male cranium is long and rugged, heavily worn upper teeth.

• The earliest representatives of anatomically fully modern humans (Homo sapiens sapiens) are currently known from Africa and the Levant. These later fossils are known from the tip of South Africa (Klasies River Mouth, c. 100,000 years) to the Middle East (Qafzeh and Skhul, at c. 90,000-130,000 years), as well as elsewhere in Ethiopia (Omo I at >100,000 years; Aduma Middle Awash at c. 80,000 years).

Herto and the Molecular Evidence

• The origins of modern humans have been the topic of heated debate over the last 25 years. Molecular studies show that the genetic diversity among human populations from Africa is greater than that seen in other regions (Templeton in Nature 2002; 416:45). Some have interpreted the genetic and fossil data to indicate that modern humans arose first in Africa and then spread outward. This is the "Out of Africa" hypothesis most strongly articulated by Christopher Stringer of the Natural History Museum in London and Günter Braüer in Hamburg.

• Other workers have questioned these interpretations by invoking uncertainties about prehistoric population size, gene flow, and mutation rates that affect interpretations of genetic data. On the fossil side, these critics have noted that African fossils of appropriate antiquity were scattered, and often ill-dated, and incomplete.

• As an alternative to the "Out of Africa" hypothesis, a "multiregional" model was proposed by several workers. This held that modern humans evolved in different parts of the Old World at roughly the same time, from ancient local populations (for instance, Europeans evolving directly from neanderthals). Several variants of these models have emerged during the course of the debate. The Herto finds add a new fossil dimension to the debate.

• Most workers are now likely to cite the available genetic data as evidence that African populations of this age were extremely successful. Current evidence suggests that their genes appear to dominate the modern human gene pool. And even if descendants of the Herto people interbred with surviving Neanderthal populations, the latter appear to have contributed very little to the modern human gene pool. In this sense, we are all African.

Herto and the Neanderthals

• Since the discovery of neanderthal fossils in Europe during the mid-1800s, the relationships of these distinctive human forms have been debated. Known from hundreds of fossils throughout Europe and western Asia, the neanderthals evolved from earlier hominids such as those found at Atapuerca in Spain, dated to around 400,000 years ago. Neanderthals most likely arose as a consequence of adapting to the glacial conditions that repeatedly affected parts of Europe during the last several hundred thousand years. The most recent neanderthals known are from peninsular Europe (Spain and Portugal) and date to only 30-35,000 years ago.

• Some scientists argue that neanderthals played a role in the origins of modern humans, either by evolving into anatomically modern Europeans (the "Cro-Magnons") or by interbreeding with anatomically modern humans from other regions.

• Some other workers interpret neanderthals as an evolutionary side branch that went extinct when anatomically modern humans arrived in western Europe.

• Recent studies of ancient DNA from neanderthal bones have been argued by most workers to support the idea of neanderthal extinction, but these results have been questioned by a few.

• Professor F. Clark Howell of U.C. Berkeley, a co-author of the Herto study, says: "These well-dated and anatomically diagnostic Herto fossils are unmistakably non-neanderthal. They show that near-humans had evolved in Africa long before the European Neanderthals disappeared. They thereby demonstrate conclusively that there was never a "neanderthal" stage in human evolution."

• The Herto fossils are African in origin, older than any other anatomically modern human fossils yet known. They are transitional from earlier and more primitive fossils also from Africa. They therefore provide strong support for the hypothesis that modern humans evolved in Africa and subsequently spread into Eurasia. Howell says that the Herto discoveries highlight the need for reinvigorated exploration of areas elsewhere in Africa, as well as the Middle East and eastern Asia.

The Herto Reconstructions

While team members conducted the comparative research on the fossils, scientific illustrator Jay Matternes of the Middle Awash team worked with the most complete adult male cranium to establish what the living Herto man might have looked like. More detailed than police sketches based on skulls from modern forensic cases, Matternes' reconstructions individualize this fossil man of Herto.

The Age

• Determining the age of the new fossils was a key factor in establishing their evolutionary significance. Fossils of this antiquity are difficult to place in time because they lie beyond the effective reach of radiocarbon (C-14) dating and also are difficult to date by most other methods. The ages of other, more ancient fossils recovered by the team have been determined by using the argon-argon (Ar/Ar) laser heating method to date volcanic layers which often overlie and underlie fossil-containing beds. This same technique was employed to date the Herto fossils.

• Dr. Paul Renne at the Berkeley Geochronology Center led the Ar/Ar laboratory work. This technique is a highly accurate method that determines the time elapsed since a volcanic ash (or tuff) is super-heated in a volcanic eruption. Argon gas trapped in the ash minerals is measured. This gas is a radioactive decay product of natural potassium and accumulates at a known rate in such volcanic products.

• A key volcanic horizon below the fossils was dated to 226,000 years, and this provided a maximum age for the Herto remains. Pumices and obsidian in the fossil-bearing layer provided an age of 160,000 years when subjected to this method.

• To determine the youngest possible age for the fossils, mineral grains from an overlying volcanic ash horizon were dated by the Ar/Ar technique. Unfortunately, this sample was found to contain only contaminating crystals from older eruptions. However, fresh non-contaminant shards of volcanic glass in this upper volcanic horizon were found to provide the chemical key to accurate age assessment.

• Dr. Giday WoldeGabriel of Los Alamos National Laboratory in New Mexico conducted chemical analysis of the major constituents of the volcanic glass found in the ash overlying the fossils. The trace elements within the same glass were measured by Dr. William Hart of Miami University in Oxford, Ohio. This was a separate and confirmatory test. The combined results allowed the investigators to correlate this tuff with samples of ash that had been collected by geologist Dr. Shigehiro Katoh at the site of Konso in southern Ethiopia, 600 kilometers south of Herto. Since each volcanic eruption produces glass with a distinctive chemical fingerprint distributed over a broad geographic area, volcanic horizons from different prehistoric drainage basins can often be correlated. The upper tuff at Herto was correlated chemically with the tuff from Konso. Six meters above the correlative Konso tuff is a second, younger tuff dated to 154,000 years by the Ar/Ar method. This correlation and dating provided the "capping" minimum age for the Herto hominids, which are therefore firmly placed within the 154,000 to 160,000 year window of time.

Human Evolution in the Middle Awash

• Tim White, one of the leaders of the Middle Awash research team, says "The new finds show that this area of Africa was inhabited by a series of human ancestors from Ardipithecus at 6 million years ago, all the way through to the Herto people at 160,000 years ago. This succession is unparalleled by any other research area in the world." White notes that the kilometer-thick sediments of the Middle Awash are ten times deeper than those exposed at the famous Olduvai Gorge in Tanzania. Olduvai's oldest rocks are only 1.8 million years old.

• The Middle Awash team's previous discoveries include Ardipithecus. This 4.4 to 5.8 million year old genus was announced in 1994 and 2001 as the first and most apelike hominid yet known. Another new species called Australopithecus garhi recovered from 2.5-million-year-old sediments at Bouri was announced in 1999. This creature was found with the earliest evidence of stone tool use for animal butchery. Last year the team reported a million-year-old fossil skullcap attributed to Homo erectus. This discovery showed that Asian and African populations were of the same species one million years ago.

Middle Awash Pleistocene Homo Finds

The Middle Awash Project

• The Middle Awash research team includes over 45 scientists from 14 different countries, specializing in geology, archaeology, and paleontology.

• The Middle Awash project operates under permit from the Ethiopian Authority for Research and Conservation of Cultural Heritage of the Ethiopian Ministry of Youth, Sports and Culture. The team conducts three months of field research each autumn.

• The Middle Awash research project was initiated in 1981 by J. Desmond Clark, who published a monograph on earlier Bouri stone tool assemblages and studied the Herto assemblages before he passed away in February of 2002 (see tributes at http://socrates.berkeley.edu/~lhesjdc1/).

• All fossils found in Ethiopia are prepared, studied, and permanently curated at the National Museum of Ethiopia.

What's Next

• Dr. Asfaw will prepare a scientific monograph on the Herto fossils.

• The Middle Awash analytical team is currently preparing publications on new fossils from c. 4.0, 4.4 and 5.8 million years ago, in addition to its ongoing field and laboratory work.

Support

• The international field research effort in the Middle Awash is supported by grants from the U.S. National Science Foundation (Physical Anthropology) and the Institute of Geophysics and Planetary Physics of the University of California at Los Alamos National Laboratory.

• Additional contributions were made by the Hampton Fund for International Initiatives at Miami University, and by the Japan Society for the Promotion of Science.

Further Information and Contacts:

• Professor Tim White co-directs the Laboratory for Human Evolutionary Studies in the Museum of Vertebrate Zoology, and teaches in the Department of Integrative Biology at U.C. Berkeley. E-mail: timwhite@socrates.berkeley.edu; tel. 510-642-2889 (no message machine).

• Professor Clark Howell co-directs the Laboratory for Human Evolutionary Studies in the Museum of Vertebrate Zoology and is emeritus professor of Anthropology at U.C. Berkeley. Professor Howell may be reached in France by telephone 33 (0) 4-90-95-90-06, or FAX 33 (0) 4-90-95-99-77 (between June 8 and 13 only). Otherwise, E-mail: fchlhes@socrates.berkeley.edu; tel. 510-642-1393.

• Dr. Giday WoldeGabriel is Geology Team Leader at Los Alamos National Laboratory. E-mail: wgiday@lanl.gov; tel. 505-667-8749.

• Dr. Paul Renne is geochronologist at the Berkeley Geochronology Center and an adjunct professor in the Department of Earth and Planetary Science at U.C. Berkeley. E-mail: prenne@bgc.org; tel. 510-644-1350 (9200).

• Professor Bill Hart chairs the Department of Geology at Miami University, Ohio. E-mail: hartwk@muohio.edu; tel. 513-529-3216.

• Dr. Berhane Asfaw and Dr. Yonas Beyene reside in Addis Ababa (7 hours ahead of EST) and will coordinate all Ethiopian-related public information with the Ministry of Youth, Sports and Culture, including the only press conference on the discovery, to be held in Addis Ababa upon embargo lift. Telephones: 251-9-22-31-94 (BA); 251-1-15-27-41 (YB); e-mail ramid@telecom.net.et.

• Professor Gen Suwa is a paleoanthropologist at the University Museum at the University of Tokyo, Japan. E-mail: suwa@um.u-tokyo.ac.jp.

• Mr. Henry Gilbert and Mr. David DeGusta are graduate students in the Department of Integrative Biology at U.C. Berkeley. Mr. Gary Richards is a graduate student in the Department of Anthropology at U.C. Berkeley. E-mail:
HG: spider@uclink.berkeley.edu; DD: degusta@uclink.berkeley.edu; GR: grichard@uclink.berkeley.edu; tel. 510-642-7952.

Visuals:

• Photographs are available from Robert Sanders, Media Relations, Public Affairs, U.C. Berkeley. Telephone (510) 643-6998; E-mail: rls@pa.urel.berkeley.edu

• Videotape segments are available from Julie Huang, Media Relations, Public Affairs, U.C. Berkeley. Telephone (510) 642-6051; E-mail: jch@pa.urel.berkeley.edu

• Still photographs documenting these discoveries, including more field shots as well as laboratory shots of specimens and scientists, are all available through David L. Brill Photography, 552 Hwy. 279, Fairburn, GA 30213, USA: Phone/Fax: 770-461-5488. E-mail: brill@mindspring.com. Brill has a special website with visuals to help journalists and editors choose images and tell the Herto story.

• Artist's reconstructions are available in nine standard anatomical views from Mr. Jay Matternes, e-mail jmatternes@cs.com; tel. 703-978-4823.