EARLIEST HOMININS, PRIMATES AND APES

HOMININS, APES AND MONKEYS

20120201-Skelet_mens_&_gorilla.JPG
human an gorilla skeletons Hominins are defined as creatures that stand upright and walk and run primarily on two legs, while apes are creatures that hunch over and, although capable of walking on two legs, prefer to use their arms when moving on the ground. Before the mid 2000s, scientists often referred to hominins as hominids. Hominids are all modern and extinct great apes: gorillas, chimps, orangutans and humans, and their immediate ancestors. Not gibbons. Hominins are any species of early human that is more closely related to humans than chimpanzees, including modern humans themselves.

Scientists have found fossils of 5,000 individual hominins as far back as 4.4 million years, perhaps 7 million years. The earliest hominins, the genus Australopethecus, possessed long arms, short legs, a large small brain and a large face. These creatures would appear to us today as more ape-like than human-like. So far the earliest hominins species have been discovered only in eastern, northern and south Africa. Scientists describe Africa as the "cradle of mankind" because all of the oldest hominin remains have been found there.

About 25 million years ago the line that would eventually lead to apes split from the old world monkeys. Between 20 million and 14 million years ago orangutans split off from the other “great apes,” chimpanzees, gorillas and humans. Between 14 million and 5 million years ago numerous species of early apes spread across Asia, Europe and Africa.

What distinguishes an ape from a monkey is the fact that apes don’t have a tail. Humans are apes. They are just as hairy as other apes, but their hair is shorter and finer. Apes are regarded as more intelligent than monkeys. They have rapid eye movement and may dream. They can recognize themselves in a mirror while monkeys think they are confronted with another monkey. Apes and humans are the only creatures that have spindle cells — large cigar-shaped cells neurons linked with emotion, problem-solving, a moral sense and a feeling of free will — in their brains.

Research by geneticists in the mid 2000s determined that the human genome and chimpanzees are only different by 1.23 percent. The one small percentage difference encompasses 35 million individual chemical changes accumulated over the 5 million to 7 million years during which the species evolved apart. Put another way humans and chimpanzees share 98.77 percent of the same genetic material. Not everyone likes this figure. A study in Japan however that 15 percent of genes of humans and chimpanzees are different.

Websites and Resources on Hominins and Human Origins: Smithsonian Human Origins Program humanorigins.si.edu ; Institute of Human Origins iho.asu.edu ; Becoming Human University of Arizona site becominghuman.org ; Talk Origins Index talkorigins.org/origins ; Last updated 2006. Hall of Human Origins American Museum of Natural History amnh.org/exhibitions ; Wikipedia article on Human Evolution Wikipedia ; Human Evolution Images evolution-textbook.org; Hominin Species talkorigins.org ; Paleoanthropology Links talkorigins.org ; Britannica Human Evolution britannica.com ; Human Evolution handprint.com ; National Geographic Map of Human Migrations genographic.nationalgeographic.com ; Humin Origins Washington State University wsu.edu/gened/learn-modules ; University of California Museum of Anthropology ucmp.berkeley.edu; BBC The evolution of man" bbc.co.uk/sn/prehistoric_life; "Bones, Stones and Genes: The Origin of Modern Humans" (Video lecture series). Howard Hughes Medical Institute.; Human Evolution Timeline ArchaeologyInfo.com ; Walking with Cavemen (BBC) bbc.co.uk/sn/prehistoric_life ; PBS Evolution: Humans pbs.org/wgbh/evolution/humans; PBS: Human Evolution Library www.pbs.org/wgbh/evolution/library; Human Evolution: you try it, from PBS pbs.org/wgbh/aso/tryit/evolution; John Hawks' Anthropology Weblog johnhawks.net/ ; New Scientist: Human Evolution newscientist.com/article-topic/human-evolution; Fossil Sites and Organizations: The Paleoanthropology Society paleoanthro.org; Institute of Human Origins (Don Johanson's organization) iho.asu.edu/; The Leakey Foundation leakeyfoundation.org; The Stone Age Institute stoneageinstitute.org; The Bradshaw Foundation bradshawfoundation.com ; Turkana Basin Institute turkanabasin.org; Koobi Fora Research Project kfrp.com; Maropeng Cradle of Humankind, South Africa maropeng.co.za ; Blombus Cave Project web.archive.org/web; Journals: Journal of Human Evolution journals.elsevier.com/; American Journal of Physical Anthropology onlinelibrary.wiley.com; Evolutionary Anthropology onlinelibrary.wiley.com; Comptes Rendus Palevol journals.elsevier.com/ ; PaleoAnthropology paleoanthro.org.

Timeline of Monkey, Ape and Hominin Development

395 million years ago: Tetrapods evolve from lobe-finned fish, as animals move on to the land. [Source: Alok Jha, The Guardian, June 5, 2013]

55 million years ago: Archicebus achilles living in what is now China.

47 million years ago: Darwinius masillae living in Messel pit area of what is now modern Germany.

Between 8 million and 4 million years ago: First the gorillas, and then chimpanzees and bonobos split off from the evolutionary lineage that led to humans. 3.8 million years ago: Australopithecus afarensis, an ape-like hominin living in Africa. Most famous fossil is Lucy.

300,000 years ago: Homo sapiens evolves in Africa.

Between 125,000 and 60,000 years ago: Homo sapiens leaves Africa.

Earliest Known Primate: A Tiny, Insect-Eating Creature from China

Archicebus

The oldest primate fossils date to around 55 million years ago. There is circumstantial evidence based on mathematics and probability that they lived as far back as 80 million years which would have made them contemporaries of the dinosaurs.

Archicebus achilles, a tiny-insect-eating creature that lived 55 million years ago present-day China, is regarded as the ancestor of all monkeys, apes and humans Alok Jha wrote in The Guardian: “A tiny animal with slender limbs, a long tail and weighing in at no more than 30 grams, has become the earliest known primate in the fossil record. Archicebus achilles lived on a humid, tropical lake shore 55 million years ago in what is now China and is the ancestor of all modern tarsiers, monkeys, apes and humans. Scientists found the fossil, whose name translates as "ancient monkey", in the Hubei province of China about a decade ago but it hasn't received detailed analysis until now. [Source: Alok Jha, The Guardian, June 5, 2013 |=|]

“About seven centimeters long, Archicebus lived in the trees and its small, pointed teeth are evidence that its diet consisted of insects. The fossil's large eye sockets indicate a creature with good vision and, according to scientists, it probably hunted during daytime. Xijun Ni of the Chinese Academy of Sciences, who led the study of the fossil, described the animal as having a very long tail, slender limbs, a round face and feet capable of grasping. "Maybe it would also have had colours and it would have preyed on insects," he said. A full description of the fossil is published in the latest edition of Nature. |=|

“The analysis shows that the fossil had a mixture of features found in modern-day tarsiers, an ancient group of primates that is now restricted to the islands of South East Asia, and others found in anthropoids, the lineage through which monkeys, apes and humans later evolved. Whereas Archicebus's foot looks like that of a modern-day marmoset, for example, the heel bone looks more like those seen in the earliest fossil anthropoids. |=|

“Chris Beard of the Carnegie Museum of Natural History in Pittsburgh, a co-author on the Nature paper, added that, because the animal was so small and "active metabolically, it was probably quite a frenetic animal, you could even think anxious. Very agile in the trees, climbing and leaping around in the canopy. The world it inhabited along that lake shore in central China was amazing – hot, humid, very tropical." |=| “Archicebus was alive during a period of intense global warming known as the palaeocene-eocene thermal maximum, a time when palm trees would have been growing as far north as Alaska. Dr Christophe Soligo, a biological anthropologist at University College London, said the discovery of the fossil was a significant contribution to scientific knowledge of early primate evolution. "It does not only contribute new fossil material to a period for which very little is preserved, but it contributes a new specimen that is astonishingly complete for its age." |=|

“To study the delicate skeleton without damaging it, scientists created a high-resolution, digital reconstruction of the fossil using x-rays at the European Synchrotron Radiation Facility in Grenoble, France. Dr Jerry Hooker, a palaeontologist at the Natural History Museum in London, said: "Most mammal fossils, including those of primates, are fragmentary, usually consisting of isolated teeth or jaws, sometimes also other skeletal elements, and we have learned a lot from these. However, to have a 50 percent complete articulated skeleton of a primitive primate is much more instructive in terms of estimating lifestyle and relationships."” |=|

Ida: the 47-Million-Year-old “Missing Link”

In a review of the book: “The Link: Uncovering Our Earliest Ancestor” by Colin Tudge with Josh Young, Guy Gugliotta wrote in the Washington Post: “In 2006, paleontologist Jorn Hurum, of the University of Oslo's Natural History Museum, was shown the remains of a small, (22 inches) juvenile female primate from the oil shales of the Messel Pit, near Frankfurt, Germany, one of Europe's most famous fossil beds. The fossil had been discovered in 1983 by a private collector who wanted to sell it. His asking price was $1 million. Hurum was immediately smitten, for the find "represented a once-in-a-lifetime experience for any paleontologist." The museum bought it. [Source: Guy Gugliotta, Washington Post, June 28, 2009 ||=||]

“Hurum assembled a team of experts to analyze and describe the fossil, a process that has thus far taken three years. The team concluded that "Ida," so named in honor of Hurum's daughter, shared characteristics with evolutionary lineages that led both to modern lemurs and to the anthropoids — including humans. "In other words," Tudge writes, "Ida appears to be an in-between species, or one of the long-sought missing links in evolution." ||=||

“In their peer-reviewed paperin the online scientific journal PLoS One, Hurum and his team say Ida "could represent a stem group from which later anthropoid primates evolved, but we are not advocating this here." Tudge describes Ida's world, a tropical forest with a volcanic lake that one day belched a gigantic bubble of toxic gas that asphyxiated this small creature and plunged it into the mud for all eternity. ||=||

"The Link" isn't just about a monkey fossil. It's about paleontology and paleontologists, warts and all. As noted, Hurum bought his fossil at an annual fair in Hamburg, Germany, from a collector, and paid big bucks for it. Many scientists regard such transactions as mortal sin, for they can encourage looting and the destruction of fossil sites, damaging ancient contexts that can never be reconstructed. In Tudge's telling, Hurum carefully selects his research team, knowing that it must be not only expert but also beyond professional reproach, because colleagues will relentlessly scrutinize its work. He needs a primate specialist. He needs a tooth expert. He needs somebody who knows the Messel Pit.” ||=||

Books: “The Link: Uncovering Our Earliest Ancestor” by Colin Tudge with Josh Young (Little, Brown, 2009); “Origins: The Story of the Emergence of Humans and Humanity in Africa” edited by Geoffrey Blundell (Double Storey, 2006)

Development of Early Primates, Lemurs and Monkeys

Alok Jha wrote in The Guardian: ““The Archicebus skeleton is about 7 million years older than the oldest currently known fossil primate skeletons, including Darwinius massilae from Messel in Germany, an extremely well-preserved fossil was that reported by scientists in 2009. Better known as Ida, it was originally thought to be a direct ancestor of the primate lineage leading to monkeys, apes and humans – but further analysis suggests Ida is closer to early lemurs. [Source: Alok Jha, The Guardian, June 5, 2013 |=|]

“The discovery of Archicebus in China lends weight to the idea that the first and most pivotal steps in primate evolution, including the beginnings of anthropoid evolution, almost certainly took place in Asia, rather than Africa. "The evidence that early primate revolution was restricted to Asia is becoming more compelling by the day," said Beard. "It consists of two different types of data – the first is genomic. If we sequence the DNA of living primates and other mammals, we find out that the closest living relatives of primates are animals like tree shrews and flying lemurs and these are animals that only live today in Asia, specifically south-eastern Asia." |=|

“The second strand of evidence comes from the fossil record. There is some evidence of primates living in Africa about 55 million years ago, but the knowledge is patchy and comes only from a few bones and teeth. "Africa at this point in time was an island continent with a very endemic and specialised mammal fauna that in some ways resembles the modern mammal fauna of Australia in the sense that it's strange – it's not like what we see on other continents," said Beard. |=|

“At some point, the descendants of Archicebus split into the lineages that would later evolve into tarsiers and anthropoids. The latter would then have made their journey to Africa and, millions of years later, evolved into humans. "We do know that early anthropoids and early fossil relatives were somehow able to make it to Africa by the end of the Eocene, roughly 38 million years ago is our best estimate," said Beard. "We still don't know how these Asian anthropoids, which had been evolving in Asia for around 20 million years by this time, made it to Africa. But we know it could not have been easy." |=|

“At the time, Africa was an island and had yet to collide with the south western side of the continent of Asia. The early primates somehow had to cross open water in order to colonise Africa. "It couldn't have been easy but they did and, after that, obviously the story changed and Africa became a pivotal centre for anthropoid evolution," said Beard.

Early Primates and Apes

One of the earliest primates so far discovered is a 33 million year old arboreal animal nicknamed the "dawn ape" found in the Egypt's Faiyum Depression. This fruit-eating creature weighed about eight pounds (three kilograms) and had a lemur-like nose, monkey-like limbs and the same number of teeth (32) as apes and modern man.

Fossils of 20.6 million-year-old common ancestor of man and apes was unearthed in Uganda in the 1960s. The animals was about 1.2 meters tall and weighed between 40 and 50 kilograms and was described by thought as a "cautious climber."

In 2011, Reuters reported: Ugandan and French scientists had discovered a fossil of a skull of a tree-climbing ape from about 20 million years ago in Uganda's Karamoja region. The scientists discovered the remains in July while looking for fossils in the remnants of an extinct volcano in Karamoja, a semi-arid region in Uganda's northeastern corner. "This is the first time that the complete skull of an ape of this age has been found. It is a highly important fossil," Martin Pickford, a paleontologist from the College de France in Paris, said. [Source: Elias Biryabarema, Reuters, August 2, 2011]

Pickford said preliminary studies of the fossil showed that the tree-climbing herbivore, roughly 10-years-old when it died, had a head the size of a chimpanzee's but a brain the size of a baboon's, a bigger ape. Bridgette Senut, a professor at the Musee National d'Histoire Naturelle, said that the remains would be taken to Paris to be x-rayed and documented before being returned to Uganda. Uganda's junior minister for tourism, wildlife and heritage said the skull was a remote cousin of the Homininea Fossil Ape.

Human Ancestors Hunted by Raptors and Wolf-Size Creodonts

creodant

Early humans may have evolved as prey to animals such a s large birds and carnivorous mammals, rather than as predators, remains of primates that lived before our human ancestors suggest. Jennifer Viegas wrote in discoverynews: “The discovery of multiple de-fleshed, chomped and gnawed bones from the extinct primates, which lived 16 to 20 million years ago on Rusinga Island, Kenya, was announced today at the Society of Vertebrate Paleontology’s 70th Anniversary Meeting in Pittsburgh. [Source: by Jennifer Viegas, discoverynews, October 12, 2010 ^||^]

“At least one of the devoured primates, an early ape called Proconsul, is thought to have been an ancestor to both modern humans and chimpanzees. It, and other primates on the island, were also apparently good eats for numerous predators. “I have observed multiple tooth pits and probable beak marks on these fossil primates, which are direct evidence for creodonts and raptors consuming these primates,” researcher Kirsten Jenkins told Discovery News. ^||^

“Creodonts were ancient carnivorous mammals that filled a niche similar to that of modern carnivores, but are unrelated to today’s meat eaters, she explained. The Rusinga Island creodonts that fed on our primate ancestors were likely wolf-sized. “There is one site on Rusinga Island with multiple Proconsul individuals all together and these are covered in tooth pits,” added Jenkins, a University of Minnesota anthropologist. “This kind of site was likely a creodont den or location where prey could be easily acquired.” ^||^

“Analysis of tooth pits, de-fleshing marks, bone breakage patterns, gnawing and other damage to the primate bones indicate that raptors were also hunting down these distant relatives of humans. “Primatologists have observed large raptors taking monkeys from trees,” Jenkins said. “When a raptor approaches a group of monkeys, those monkeys will make alarm calls to warn their group and attempt to retreat to lower branches. The primates on Rusinga had monkey-like postcrania and likely had very similar locomotor behavior.” Jenkins is not certain what selective pressures predators placed on these very early primate ancestors to humans, but she said they “can affect behavior, group structure, body size and ontogeny (the life cycle of a single organism).”^||^

“Robert Sussman, professor of physical anthropology at Washington University in St. Louis, has long argued that primates, including early humans, evolved not as hunters but as prey of many predators, including wild dogs and cats, hyenas, eagles and crocodiles. “Despite popular theories posed in research papers and popular literature, early man was not an aggressive killer,” said Sussman, author of the book “Man the Hunted: Primates, Predators and Human Evolution.” “Our intelligence, cooperation and many other features we have as modern humans developed from our attempts to out-smart the predator. He added that the idea of man as hunter “developed from a basic Judeo-Christian ideology of man being inherently evil, aggressive and a natural killer.” “In fact, when you really examine the fossil and living non-human primate evidence, that is just not the case,” he explained. ^||^

Apes Become More Human-Like

Baboon-size apes that lived in East Africa about 15 million years ago may have spent most of its time on the ground. This finding is based on the hand, finger arm and shoulder bones from a ape called Equatorious found in 1993 in the Tugen Hills of north central Kenya. A fossil of an ape that lived 13 million years ago in Spain has been described as a common ancestor to all apes and hominins and led some to theorize that the ancestral ape that spawned gorillas, chimpanzees and human came to Africa from Eurasia.

Between 11 million and 8 million years ago gorillas split off from chimpanzees and humans. In 2007 an Ethiopian and Japanese team of scientists announced in a Nature article that they had found a 10-million-year-old ape 170 kilometers south of Addis Ababa in Ethiopia that was very similar to a gorilla that provided some grounds for pushing back the date of the split between humans and apes. The discovery also supported the theory that the apes that spawn humans originated in Africa.

Rudapithecus was the name given to a 10-million-year-old great ape unearthed in Hungary. Some have called the ape the closest fossil hunters gave come to finding a common ancestor of humans and African apes. Named after the village of Hungarian Rudabanya, near where it was found, it had a body and brain about the size of a chimpanzee. Its long arms and curved fingers indicate it spent a lot of time hanging from the branches of trees. Modest-size molars and thin tooth enamel suggested it ate soft fruits.

Split Between Apes and Hominins

Based on DNA evidence in blood proteins, molecular biologists guess that the hominin line split off from the ape line between 5 and 8 million years ago, a period of time in which little is known about apes or hominins and there is little data in the fossil record.

The generally accepted assumption is that gorillas and ancestors of chimpanzees and humans split around 6 million to 8 million years ago. Some DNA evidence seems to indicate that hominins and chimpanzees split between 5.5 million and 6.5 million years ago.

Calculations made by geneticists based on the differences between genomes indicates that the chimpanzees and hominins diverged no later than 6.3 million years ago and probably earlier than 5.4 million years ago. This finding raises questions about fossils that are more than five million years old — namely “Sahelanthropus tchadensis” and “Orrorin tugenensis — that are claimed to belong to hominin species.

A team led by David Reich of the Broad Institute in Cambridge, Massachusetts has suggested that one explanations for the discrepancy between the fossil record (that says the oldest hominin are 7 million years old) and genetic evidence (which dates hominin and chimpanzee divergence at around 5.3 million years ago) is that chimpanzees and early hominin might have had sex with each other and interbred. That could also explain why some early hominins have strange mixture of human and chimpanzee traits. One should not jump to too many conclusions though as there is still a lot of uncertainty over dating and inferences made from small quantities of fossils.

Last Common Ancestor of Humans and Chimpanzees

The last common ancestor of humans and chimpanzees are believed to have had shoulders similar to those of modern African apes, a finding supports the theory that early humans moved away from life in trees gradually. Charles Q. Choi wrote in Live Science: “The human lineage diverged from that of chimpanzees, humanity's closest living relative, about 6 million or 7 million years ago. Knowing the characteristics of the last common ancestor of humans and chimps would shed light on how the anatomy and behavior of both lineages evolved over time, "but fossils from that time are rare," said lead author of the new study Nathan Young, an evolutionary biologist at the University of California, San Francisco. [Source: Charles Q. Choi, Live Science, September 8, 2015 +]

“There are currently at least two competing scenarios for what the last common ancestor might have looked like. One suggests that similarities seen in modern African apes, such as in chimps and gorillas, were inherited from the last common ancestor, meaning that modern African apes may reflect what the last common ancestor was like. "A lot of people use chimpanzees as a model for the last common ancestor," Young told Live Science. +\

“The other scenario suggests these similarities instead evolved independently in modern African apes, and that the last common ancestor may have possessed more-primitive traits than those seen in modern African apes. For instance, instead of knuckle-walking on the ground like chimps and gorillas do, the last common ancestor may have swung and hung from tree branches like orangutans, which are Asian apes. Humans aren't the only species that have evolved and changed over time — chimpanzees and gorillas have evolved and changed over time, too, so looking at their modern forms for insights into what the last common ancestor was like could be misleading in a lot of ways," Young said. +\

“The ancestral state of the shoulder is key to understanding human evolution, because the shoulder is linked to many important shifts in behavior in the human lineage. Shoulder evolution could help show when early human ancestors began using tools more, spent reduced time in trees and learned to throw weapons. However, the human shoulder possesses a unique combination of features that makes it difficult to reconstruct the body part's history. For instance, while humans are most closely related to knuckle-walking chimps, in some respects the human shoulder is more similar in shape to that of tree-dwelling orangutans. +\

“To see what the shoulder of the last common ancestor might have looked like, researchers generated 3D shoulder models from museum specimens of modern humans, chimps, bonobos, gorillas, orangutans, gibbons and monkeys. The scientists compared these data with 3D models that other scientists previously generated of ancient, extinct relatives of modern humans, such as Australopithecus afarensis, Australopithecus sediba, Homo ergaster and Neanderthals. +\ Australopithecines such as Australopithecus afarensis and Australopithecus sediba are the leading candidates for direct ancestors of humans. "Recent data from the australopithecines helped us now test different models of human evolution," Young said. +\

“The scientists found the strongest model showed the human shoulder gradually evolving from an African apelike form to its modern state. "We found australopithecines were perfect intermediate forms between African apes and modern humans," Young said. This finding suggests the human lineage experienced a long, gradual shift out of the trees and increased reliance on tools as it became more terrestrial, he said. "These results pretty much confirm that the simplest explanation for how the human shoulder evolved is the most likely one," Young said. The scientists detailed their findings online Sept. 7, 2015 in the journal Proceedings of the National Academy of Sciences.” +\

Human-Like 5.7-Million-Year-Old Footprints in Crete

Newly discovered human-like footprints from Crete, dated to 5.7 million years ago, challenges the established narrative of early human evolution that our earliest ancestors evolved in Africa and has ape-like feet. Uppsala University reported: “Ever since the discovery of fossils of Australopithecus in South and East Africa during the middle years of the 20th century, the origin of the human lineage has been thought to lie in Africa. More recent fossil discoveries in the same region, including the iconic 3.7 million year old Laetoli footprints from Tanzania which show human-like feet and upright locomotion, have cemented the idea that hominins (early members of the human lineage) not only originated in Africa but remained isolated there for several million years before dispersing to Europe and Asia. The discovery of approximately 5.7 million year old human-like footprints from Crete, published online this week by an international team of researchers, overthrows this simple picture and suggests a more complex reality. [Source: Uppsala University, Science Daily, August 31, 2017, “Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?”, Gerard D. Gierlinskia et al. Proceedings of the Geologists' Association, 2017 DOI: 10.1016/j.pgeola.2017.07.006 ~||~]

“The footprints were discovered by Gerard Gierlinski (1st author of the study) by chance when he was on holiday on Crete in 2002. Gierlinski, a paleontologist at the Polish Geological Institute specialized in footprints, identified the footprints as mammal but did not interpret them further at the time. In 2010 he returned to the site together with Grzegorz Niedzwiedzki (2nd author), a Polish paleontologist now at Uppsala University, to study the footprints in detail. Together they came to the conclusion that the footprints were made by hominins. ~||~

“Human feet have a very distinctive shape, different from all other land animals. The combination of a long sole, five short forward-pointing toes without claws, and a hallux ("big toe") that is larger than the other toes, is unique. The feet of our closest relatives, the great apes, look more like a human hand with a thumb-like hallux that sticks out to the side. The Laetoli footprints, thought to have been made by Australopithecus, are quite similar to those of modern humans except that the heel is narrower and the sole lacks a proper arch. By contrast, the 4.4 million year old Ardipithecus ramidus from Ethiopia, the oldest hominin known from reasonably complete fossils, has an ape-like foot. The researchers who described Ardipithecus argued that it is a direct ancestor of later hominins, implying that a human-like foot had not yet evolved at that time. ~||~

Sahelanthropus “The new footprints, from Trachilos in western Crete, have an unmistakably human-like form. This is especially true of the toes. The big toe is similar to our own in shape, size and position; it is also associated with a distinct 'ball' on the sole, which is never present in apes. The sole of the foot is proportionately shorter than in the Laetoli prints, but it has the same general form. In short, the shape of the Trachilos prints indicates unambiguously that they belong to an early hominin, somewhat more primitive than the Laetoli trackmaker. They were made on a sandy seashore, possibly a small river delta, whereas the Laetoli tracks were made in volcanic ash. ‘'What makes this controversial is the age and location of the prints,' says Professor Per Ahlberg at Uppsala University, last author of the study. ~||~

“At approximately 5.7 million years, they are younger than the oldest known fossil hominin, Sahelanthropus from Chad, and contemporary with Orrorin from Kenya, but more than a million years older than Ardipithecus ramidus with its ape-like feet. This conflicts with the hypothesis that Ardipithecus is a direct ancestor of later hominins. Furthermore, until this year, all fossil hominins older than 1.8 million years (the age of early Homo fossils from Georgia) came from Africa, leading most researchers to conclude that this was where the group evolved. However, the Trachilos footprints are securely dated using a combination of foraminifera (marine microfossils) from over- and underlying beds, plus the fact that they lie just below a very distinctive sedimentary rock formed when the Mediterranean sea briefly dried out, 5.6 millon years ago. By curious coincidence, earlier this year, another group of researchers reinterpreted the fragmentary 7.2 million year old primate Graecopithecus from Greece and Bulgaria as a hominin. Graecopithecus is only known from teeth and jaws. ~||~

“During the time when the Trachilos footprints were made, a period known as the late Miocene, the Sahara Desert did not exist; savannah-like environments extended from North Africa up around the eastern Mediterranean. Furthermore, Crete had not yet detached from the Greek mainland. It is thus not difficult to see how early hominins could have ranged across south-east Europe and well as Africa, and left their footprints on a Mediterranean shore that would one day form part of the island of Crete. 'This discovery challenges the established narrative of early human evolution head-on and is likely to generate a lot of debate. Whether the human origins research community will accept fossil footprints as conclusive evidence of the presence of hominins in the Miocene of Crete remains to be seen,' says Per Ahlberg.” ~||~

Messy Models of the Evolution of Man

Early attempts to plot the course of human evolution tried to present nice neat linear models with one species leading directly to another. The more discoveries that were made the less the neat models became.

Modern models of human evolution look like groups of trees with lots of entangled branches — some that lead to dead ends and others that continue on and interconnect to other branches. In the old days many thought who studied early man were regarded as “lumpers” because they tended to lump discoveries into group. In recent years they have taken a backseat too “splitters,” who shy away from grouping new discoveries and instead often define them as new, separate species.

New discoveries have also debunked theories that human evolution was marked by a series of nice, neat progressions and advancements. Sometimes new discoveries dated to a certain period seem more primitive than older finds.

Some features in one species appear and then disappear and then re-emerged in later species, making the features insignificant as some sort of milestone. Bernard Wood of George Washington University told Newsweek, “Similar traits evolved more than once, which means you can’t use them as gold-plated evidence that one fossil is descended from another or that having an advanced trait means a fossil was a direct ancestor of modern humans.”

World's Oldest Hominin, from 7 Million Years Ago?

20120201-Sahelanthropus_tchadensis_Toumai chad 2.jpg
Sahelanthropus tchadensis The oldest fossils that have been widely accepted at least of possibly belonging to hominin species are 7-million-year-old “Sahelanthropus tchadensis” and 6-million-year-old “Orrorin tugenensis . Many though think these fossils belong to ape species not hominin ones. (See Early Hominins)

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.

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