The earliest known hominins were for a long time were thought to come from the genus “Australopithecus”, which first appeared between 3 million and 4 million years ago. But now, after discoveries made in the 1990s and early 2000s, many scientists think the oldest hominins belong to another genus, “Ardipithecus” , that first appeared at least 4 million years ago and may be as old as six million years old. Some even older creatures that have been discovered may also be hominins. A genus is a class of animals or plants that usually consist of more than one species.

Categories with related articles in this website:
Early Hominins and Human Ancestors (23 articles); Neanderthals, Denisovans, Hobbits, Stone Age Animals and Paleontology (25 articles); Modern Humans 400,000-20,000 Years Ago (35 articles); First Villages, Early Agriculture and Bronze, Copper and Late Stone Age Humans (33 articles)

Websites and Resources on Hominins and Human Origins: Smithsonian Human Origins Program ; Institute of Human Origins ; Becoming Human University of Arizona site ; Talk Origins Index ; Last updated 2006. Hall of Human Origins American Museum of Natural History ; Wikipedia article on Human Evolution Wikipedia ; Human Evolution Images; Hominin Species ; Paleoanthropology Links ; Britannica Human Evolution ; Human Evolution ; National Geographic Map of Human Migrations ; Humin Origins Washington State University ; University of California Museum of Anthropology; BBC The evolution of man"; "Bones, Stones and Genes: The Origin of Modern Humans" (Video lecture series). Howard Hughes Medical Institute.; Human Evolution Timeline ; Walking with Cavemen (BBC) ; PBS Evolution: Humans; PBS: Human Evolution Library; Human Evolution: you try it, from PBS; John Hawks' Anthropology Weblog ; New Scientist: Human Evolution; Fossil Sites and Organizations: The Paleoanthropology Society; Institute of Human Origins (Don Johanson's organization); The Leakey Foundation; The Stone Age Institute; The Bradshaw Foundation ; Turkana Basin Institute; Koobi Fora Research Project; Maropeng Cradle of Humankind, South Africa ; Blombus Cave Project; Journals: Journal of Human Evolution; American Journal of Physical Anthropology; Evolutionary Anthropology; Comptes Rendus Palevol ; PaleoAnthropology

World's Oldest Hominin From Chad?

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Sahelanthropus tchadensis
In July 2002, French scientists announced they had found a hominin skull, dated to seven millions years ago, in western Chad. About the size of a chimpanzee, it had both humanlike and apelike features and was regarded as so different from anything before it was given a new genus and species name,”Sahelanthropus tchadensis” . Many refer to it by its nickname, Toumai (“Hope of Life” in the local Goran language), a name often given to children born in Chad during the dry season.

Some called “Sahelanthropus tchadensis” the greatest discovery in 80 years. A cranium and two lower jaw fragments and three teeth were found in the Djurab Desert in the Sahel region of Chad by a team led by Dr. Michel Brunet of the University of Pottiers in France. The discovery was a shock to scientists because it age, complexity and location. The braincase was apelike (small and about the size of a chimpanzee’s) but the face and teeth were more humanlike. The lower face did not protrude like an ape’s and the brow ridges were likes those on later hominins. The spinal column’s entry point suggested that it walked upright. The fossils were found in July 2001 by a Chadian named Ahounta Djumdoumalbaye. The discovery site was 1,500 miles west of more familiar hominin sites in Kenya and Ethiopia and at one time was part of a lush forest. The fossils were dated based on known dates of fossils found near it (a lack volcanic ash layers made it difficult to date the fossils precisely) .

The discovery threw a monkey wrench into the neat linear models of evolutionary progression to modern man. Toumai’s face seemed more humanlike than Lucy’s, which has led some to conclude that maybe Australopithecus (See Australopithecus section) was not an ancestor of modern man and Australopithecus was a side-branch dead end on the evolutionary tree. Many scientists favor a “busy tree” model with many species and branches.

Research that appeared in the journal Nature in April 2005 — namely that certain features of the jawbones found were similar to those of later hominins’suggests that the “Sahelanthropus tchadensis” is indeed a hominin. The evidence wasn’t conclusive but it was strong. It still isn’t clear that creature walked upright.DNA evidence that indicates hominins and chimpanzees split between 5.5 million and 6.5 million years ago raises questions whether these were hominins.

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Sahelanthropus tchadensis

Other Very Old Hominins

In December 2000, a team from the College de France in Paris and the Community Museum of Kenya announced that had found a 6-million-year-old hominin fossil in the Tugen Hills of Kenya's Baringo district. The hominin was called “ Orrorin tugenensis” . “Orrorin” means “Millennium Man.”

Many scientists reject the notion that this creature was a hominin. The fossils consisted of a few teeth and a femur. Critics claim the creature has apelike teeth and there is nothing about the femur that suggests that "Orrorin tugenensis” didn't walk on all fours. In any case few teeth and a femur isn’t much to go on.

In August 2004, research published in the journal Science reported that CT scans of "Orrorin tugenensis"’s femur suggests that the creature walked upright. The bone was about the size of a chimpanzees but thinner on the top of neck connecting the ball and shaft than it was ta the bottom, features consistent with walking upright. As with “Sahelanthropus tchadensis” DNA evidence that indicates hominins and chimpanzees split between 5.5 million and 6.5 million years raises questions whether "Orrorin tugenensis” was a hominin.

A number of other fossils have been found have been claimed to be the world’s earliest hominin fossil. A jawbone with three molars, dated at 12-13 million years, discovered in the Otavi Hills of Namibia on June 4, 1991 has been claimed to the world’s earliest hominoid. A 5.6-million-year-old jaw fragment discovered in 1967 at Lothagam Lake Turkana in Kenya was claimed to belong to a very old hominin. Both claims were largely dismissed as the evidence they belonged to hominins was pretty shaky. In February 1984 an Australopithecine jawbone with two molars — dated at 4 million years ago by nearby fossils and 5.4-5.6 million years ago by rocks — was found near Lake Baringo, Kenya.

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Sahelanthropus tchadensis

Ardipithecus Ramidus Kadabba

In July 2001, scientists from the University of California, Berkeley announced that they had found 5.8 million-year-old to 5.2 million-year-old hominin fossils in Ethiopia. The hominin was called “Ardipithecus kabbada” or "Ardipithecus ramidus kabbada”. The name is derived from the Afar language. “Ardi” means “ground” and “kadabba” means “basal family ancestor.”

Many scientists believe that this is the world's oldest known hominin. The eleven “Ardipithecus kadabba” fossils that were found included jawbone with teeth, hand and foot bones, pieces of arm bone, and a piece of a collar bone. A toe bone appears to indicate that it walked upright. It’s teeth had both ape and hominin features but were relatively small, a hint of homonids to come. "Ardipithecus kadabba” is believed to have stood 1.2 meters tall (about 20 percent taller than Lucy). The size of it brain and proportions of it arms and legs were similar to those of a chimpanzee. The conclusion on upright walking was based on the fact that shape of the foot bone is consistent with that of a bipedal creatures that “toe off” when they walk.

“Ardipithecus kadabba” was discovered in the western foot hills of the Middle Awash Valley in Ethiopia and collected over four years by Yohannes Haile-Selassie, an Ethiopian graduate student at the University of California, Berkeley who has worked with evolutionary biologist Tim White. Haile-Selassie found the jawbone in September 1997 in a place called Alaya but didn't realize he had something special until he analyzed it a year later. The specimen were dated using argon-argon dating of the volcanic layers sandwiched in sediments around the fossils.

Ardipithecus Ramidus

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early hominin and pre-hominin discovery sites
In a October 2009 article in Science a creature called “Ardipithecus ramidus” was heralded by Berkeley’s Tim White as the oldest known hominin. Nicknamed “Ardi,” the 120-centimeter -tall, 4.4-million-year-old female, the article said, had an apelike head and opposable toe that allowed her to climb trees easily, but her hands, wrists and pelvis indicated she strode like modern humans and did not knuckle walk like ape. Despite her small body she had hands that were about the same size as human hands. Science called the announcement the magazine’s breakthrough story of the year.

“Ardipithecus ramidus” had a weird combination of human traits and very primitive parts that before were found only on monkeys and extinct apes form the Miocene period. It’s arms and skull have hominin features but the teeth are chimpanzeelike. It had smaller molars, larger canines, and thinner tooth enamel than Australopithecines that came later. This suggests it lived off a diet rich in easy-to-chew fruits and vegetables. No leg bones were found so it is difficult to determine whether the ancient creature could walk on two legs. Scientists say that is didn't walk solely on two legs or four legs but something in between. The name “Ardipithecus ramidus” is derived from the Afar language. “Ardi” means “ground” and “ramid” means “root.”

Pieces from 36 other “Ardipithecus ramidus” individuals have been found, collected, including a partial foot and some wrist bones. In January 2005, the discovery of fossils from nine “ Ardipithecus ramidus “ in Ethiopia dated to 4.3 million to 4.5 million years ago was reported. The fossils — mostly teeth and jaw bone fragments — were found at the As Duma site in Ethiopia’s Afar region. The teeth were similar to those of large apes and showed wear and tear consistent with a plant-based diet. Patterns of wear indicate a woodland diet of fruits and nuts. Fossils found around it belonged to forest-dwelling monkeys and antelope. Altogether the remains of 6,000 of other vertebrates have been found with the “Ardipithecus ramidus” remains.

Discovery of Ardi

Ardi skull
Ardi was found in 1994 in the Aramis areas of the Middle Awash area of Ethiopia. The fossils were impeded in rock and so delicate it took more than a decade to extract, prepare and analyze them. When Ohio State anatomist Owen Lovejoy first laid eyes on the bones in Ethiopia he told National Geographic, “My first thought was, Why did they bring us over to look at a roadkill?” It took two years just to recover the skeleton from the rock and more years to clean it and prepare it.

“Ardipithecus ramidus” was dated to be 4.4 million year old, more than a million years older than Lucy. Altogether 125 bones were picked out of the rock, yielding a partial skeleton of one individual.. They fossils included the remains of arm bones, skull shards and a tooth still imbedded in a piece of jaw.

Ardi’s fragmented and crushed skull was too fragile and incomplete to reassemble. Instead Gen Suwa, an anthropologist at the University of Tokyo, has digitally reconstructed a partial skull by taking CT scans of the pieces and then pieced them together digitally.

The first “Ardipithecus ramidus” fossils were discovered in December 1992 by Suwa in the Aramis dry streambed in the Middle Awash area of Ethiopia. The fossils were was dated to be 4.4 million years old based on the presence of volcanic tuff dated to that time. Suwa found a molar poking up out of the ground and recognized it as belonging to a hominin. A couples days late fossil hunter Alemeyehi Asfaw found a piece of child’s jaw with a first molar. The condition of the fossils was very delicate, hampering preparation and scientific description.

Suwa was working with Desmond Clark and Tim White of Berkeley. White later told National Geographic, “The milk molar was like no other hominin baby tooth I’d ever seen, and I’d seen them all. Gen and I looked at each other. We didn’t have to say anything. This was something way more primitive.”

Is Ardipithecus a Hominin?

Ardipithecus kadabba fossils
White asserted that despite his distaste for the term “ Ardipithecus kadabba” and “Ardipithecus ramidus” are “something pretty close” to missing links between chimpanzees and humans. "It's the link that's no longer missing" he said. Owen Lovejoy, an anatomist at Ohio State University, said that he found two dozen distinct traits that link “Ardipithecus ramidus” to hominins.

Based primarily in a jawbone and wrist fossils, researchers claim that “Ardi” was clearly a human ancestor and did not grow up to be an ape. White told Reuters, “People have sort of assumed that modern chimpanzees haven’t evolved very much, that the last common ancestor was more or less like a chimpanzee and that its been the human lineage that’s done all the evolving.”

It is hard to say at this time whether Australopithecus and other human ancestors evolved from Ardipithecus. There is lot of debate in the early man field now on this question. There is also a lot of debate on the question of whether or not Ardipithecus is even a hominin. Many scientists believe its odd assortment of traits make it an unusual ape rather than a hominin. Between 25 million and 5 million years ago there were a lot of different apes running around. Perhaps, maybe likely, Ardipithecus was just one of those.

Critics of of claims that “Ardipithecus kadabba” and “Ardipithecus ramidus” are hominin species claim the creatures have too many chimp-like features. In a June 2010 Science article Esteban Sarmiento of the Hyam Evolution Foundation in East Rutherford, New Jersey argued that he thought “Ardipithecus” arose before humans and apes split.

Ardipithecus and Bipedalism

The “Ardipithecus” genus were arguable the first known bipedal creatures (the main definition of a hominin). They appear to have been a quadrupedal in trees and bipedal on the ground. Their range appears to have been restricted to eastern Africa. [Source: Jamie Shreeve, National Geographic, July 2010]

“Ardipithecus” had an opposable big toe which was well suited for grasping branches but less than ideal for providing a push needed for efficient bipedal walking (Lucy had an unopposable big toe that lined up with the other toes). Scientists have said that Ardipithecus’s four other four toes provided the “push off” function. The foot of “Ardipithecus ramidus” contained a small bone called the os peroneum — which was retained in some hominin species but never found in gorillas and chimpanzees — that kept the bottom of the foot rigid and allowed the other four toes to push off the ground.

The shape of “Ardipithecus"’s pelvis and hips appears to have enabled the creature to walk bipedally and climb through the trees. In many ways the pelvis is the key to bipedalism. It had to undergo radical changes to allow walking. Chimp pelvises are narrow and long to provide rigid support when the animal is climbing trees but causes it to lurch side to side when walking upright. Australopithecus and modern human pelvises are broader and shorter, thus enlarging the attachment area for gluteal muscles that stabilize the supporting hip joint, making is easier to stand and walk.

Jamie Shreeve wrote in National Geographic, “Ardi’s upper pelvis is short and broad and shows other features rarely seen except in hominins, such as protrusions on the inside edge of the pelvis where bone was added during development to bolster support for the bipedal stride. Yet the lower pelvis is thoroughly apelike, with attachments for massive hind-limb muscles needed for effective climbing.”

Ardi’s relatively large hands and highly flexible wrist helped her move through the trees. Her fingers were long and her palm was short and flexible. This would have allowed her to walk on her palms on the top of tree but was not suited for knucklewalking like an ape. If it turns out that Ardipithecus are indeed the ancestors of humans it might mean that hominins never went through the knucklewalking phase that gorillas and chimpanzees are currently in.

Ardipithecus, Sex and Climate Theory

Ardipithecus finger bones
Scientists believe that “Ardipithecus kadabba” and “Ardipithecus ramidus” lived in the forest because: 1) their teeth indicate they ate woodland foods: and 2) their remains were found among fossils of forest dwelling plants and monkeys.

If it is indeed true that “Ardipithecus” lived in woodlands and is bipedal it means he likely developed the ability to walk in woodlands which would debunk the “savannah hypotheses” — that man first walked up right to survive in a grassland habitat — and the “climate theory” — that changes in climate which caused woodlands to change to savannahs caused early hominin to walk upright.

Lovejoy has theorized that Ardipithecus came out trees for sex. Based on the fact that the canines of Ardipithecus males are small and similar to females — unlike male apes which have large canines and use them mainly in fights with other males — Ardipithecus won over females by coming down of the trees to collect high-protein, high-fat food given to the females offspring in return for sex and bipedalism developed as a way to carry back food.

Scientists have found some evidence (from soil samples and analysis of teeth) that “Ardipithecus” lived in a savannah environment not a wooded one. Most scientists agree that a lot of analysis and research still needs to be done to make any authoritative claims about Ardi and her kin.

Image Sources: Wikimedia Commons

Text Sources: National Geographic, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Nature, Scientific American. Live Science, Discover magazine, Discovery News, Times of London, Natural History magazine, Archaeology magazine, The New Yorker, Time, Newsweek, BBC, The Guardian, Reuters, AP, AFP and various books and other publications.

Last updated September 2018

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