December 19, 2012
One-hundred years ago, on December 18, 1912, British paleontologist Arthur Smith Woodward introduced the world to a tantalizing fossil: England’s most ancient human ancestor, perhaps one of the world’s oldest hominids. Best known as Piltdown Man, the “discovery” turned out to be the biggest hoax in the history of paleoanthropology. It’s a scientific crime that researchers are still trying to solve.
Piltdown Man consists of five skull fragments, a lower jaw with two teeth and an isolated canine. The first fossil fragment was allegedly unearthed by a man digging in gravel beds in Piltdown in East Sussex, England. The man gave the skull fragment to Charles Dawson, an amateur archaeologist and fossil collector. In 1911, Dawson did his own digging in the gravel and found additional skull fragments, as well as stone tools and the bones of extinct animals such as hippos and mastodons, which suggested the human-like skull bones were of a great antiquity. In 1912, Dawson wrote to Smith Woodward about his finds. The two of them—along with Pierre Teilhard de Chardin, a Jesuit priest and paleontologist—returned to the Piltdown gravels to continue excavating. They found additional skull fragments and the lower jaw. The following year Teilhard de Chardin discovered the lone canine tooth.
Smith Woodward reconstructed the Piltdown man skull based on the available fossil evidence. His work indicated the hominid had a human-like skull with a big brain but a very primitive ape-like jaw. Smith Woodward named the species Eoanthropus dawsoni (Dawson’s Dawn Man). It was the first hominid found in England, and other anatomists took Piltdown as evidence that the evolution of a big brain was probably one of the first traits that distinguished hominids from other apes.
At the time of the discoveries, the field of paleoanthropology was still in its infancy. The only other hominid fossils that had been found by 1912 were Neanderthals in continental Europe and the even older Homo erectus of Indonesia. As additional fossils were discovered elsewhere, such as Africa and China, it became harder to see how Piltdown fit with the rest of the fossil record. The growing collection of hominid bones suggested upright walking was the first major adaptation to evolve in hominids with increases in brain size coming millions of years later after the emergence of the genus Homo. Finally, in the 1950s, it became clear why Piltdown was so odd: It was a fake.
In 1949, physical anthropologist Kenneth Oakley conducted fluorine tests on the Piltdown Man bones to estimate how old they were. The test measures how much fluoride bones have absorbed from the soil in which they’re buried. By comparing the fluoride levels to those of other buried objects with known ages, scientists can establish a relative age of the bones. With this method, Oakley determined Piltodwn Man wasn’t so ancient; the fossils were less than 50,000 years old. In 1959, anatomist Wilfrid Le Gros Clark and anthropologist Joseph Weiner took a closer look at Piltdown Man’s anatomy and realized the jaw and skull fragments belonged to two different species. The skull was most likely human while the jaw resembled an orangutan. Microscopic scratches on the jaw’s teeth revealed someone had filed them down to make them appear more like human teeth. And all of the bones had been stained to make them look old.
Since the truth about Piltdown Man was revealed, there have been many suspects implicated in the forgery. Dawson was the prime suspect. But he died in 1916, so scientists never had the chance to question his possible role in the hoax. Teilhard de Chardin, who found the isolated canine tooth on his own, is another possibility. One of Smith Woodward’s colleagues, Martin Hinton, may have also played a role. In 1978, workers found an old trunk of Hinton’s at the Natural History Museum in London. The trunk held teeth and bones stained in a similar way as the Piltodwn Man fossils. Despite much interest and speculation, no one has ever definitively tied any of these men to the hoax.
And now, a century after the announcement of Piltdown Man, scientists are still intrigued by the fake hominid’s origins. A team of 15 British researchers are using new methods to investigate the mystery. Radiocarbon dating and DNA testing will help identify exactly how old the bones are and confirm the jaw belongs to an orangutan. Chemical tests will also help the team pinpoint where the bones came from and whether they were all stained in the same way.
It will be several months before the analyses are complete. But if it turns out all the material was stained in the same way, or came from the same location, then it’s more likely that just one person was responsible for the scientific fraud. And that person is likely to be Dawson. It turns out that Dawson was responsible for at least 38 fake finds during his amateur fossil-hunting career, the Telegraph reports. Chris Stringer, an anthropologist at the Natural History Museum in London and one of the scientists investigating Piltdown, speculates in a commentary in Nature that Dawson may have committed such hoaxes in an effort to achieve scientific glory.
Stringer writes that Piltdown Man serves as a good reminder for scientists to “keep their guard up.” I think it also highlights the importance of open science in the field of paleoanthropology. The hoax wasn’t uncovered until scientists unconnected to the discovery analyzed the evidence. Today, numerous hominid species are known based on just a handful of fossils that only a handful of scientists have ever had the chance to study. In no way do I think some of these fossils might be fake. But giving other scientists greater access to the complete hominid fossil record will not only allow more errors to be detected but will also stimulate new interpretations and explanations of how our ancestors evolved.
And with that sentiment, I end my last Hominid Hunting post as I head off to a new job with Science News. I’ve enjoyed sharing my love of all things hominid with my readers, and I’ve appreciated all of the spirited feedback.
Ed. Note: Thanks, Erin, for all of your blogging the past couple of years! It’s been a thrill and best of luck to you going forward. — BW
December 10, 2012
The Smithsonian Institution’s Human Origins Initiative counts seven species as belonging to the genus Homo. But that’s just a fraction of all the species that scientists have proposed for our genus. Over the years, as researchers have realized fossils from different groupings actually come from the same species, anthropologists have tossed out the names that are no longer valid. Last spring, I highlighted several of these now-obscure names, as well as some recently proposed species that are not universally accepted. Here’s a look at four more proposed species of Homo that you probably won’t find in human evolution text books or museum exhibits.
Homo antiquus: In 1984, Walter Ferguson of Israel’s Tel Aviv University declared that Australopithecus afarensis wasn’t a real species (PDF). At the time, the known fossils of A. afarensis came from the site of Hadar in Ethiopia and Laetoli in Tanzania. There was a lot of physical variation among the bones in this combined collection, but many anthropologists thought the diversity was simply due to size differences between male and female members of the species. Ferguson, however, believed the bones actually represented more than one species. Based on the size and shape of the molars, Ferguson concluded that some of the larger jaws at Hadar matched those of Australopithecus africanus, a species that had only been found in South Africa. Other jaws in the collection had smaller, narrower Homo-like teeth, he said. The roughly three-million-year-old fossils were too ancient to fit with any of the previously described members of the genus Homo, so Ferguson created a new species name—H. antiquus. Ferguson’s species splitting had a larger implication: If Australopithecus and Homo had lived side by side for hundreds of thousands of years, it was unlikely that australopithecines were the direct ancestors of Homo. Ferguson’s work must not have been convincing. Almost 30 years later, A. afarensis is still around and few people have ever heard of H. antiquus.
Homo kanamensis: Many of Louis Leakey’s discoveries have stood the test of time. H. kanamensis is not one of them. In the early 1930s, Leakey unearthed a hominid lower jaw at the site of Kanam, Kenya. The jaw resembled those of modern people in many ways, but was thicker in some places. Leakey determined the jaw should have its own name: H. kanamensis. At about half a million years old, the species was the oldest member of Homo yet found—except, the fossil wasn’t really that ancient. Subsequent geological studies at Kanam revealed that the jaw was only a few tens of thousands of years old. And the jaw’s unusual thickness was due to an abnormal growth, suggesting H. kanamensis was nothing more than a diseased Homo sapiens.
Homo capensis: In the early 1910s, two farmers stumbled across hominid fossils, including bits of a skull, near Boskop, South Africa. The bones were passed around to many anatomists—including Raymond Dart, who later discovered the first Australopithecus fossil—before ending up in the hands of paleontologist Robert Broom. Broom estimated the brain size of the skull (PDF): a whopping 1,980 cubic centimeters (the typical modern person’s brain is around 1,400 cubic centimeters). Broom determined that the skull should be called H. capensis, also known as Boskop Man. Other specimens from South Africa were added to the species, and some scientists became convinced southern Africa was once home to a race of big-brained, small-faced people. But by the 1950s, scientists were questioning the legitimacy of H. capensis. One problem was that the thickness of the original skull made it difficult to estimate the true brain size. And even if it were 1,980 cubic centimeters, that’s still within the normal range of variation for modern people’s brains, anthropologist and blogger John Hawks explained in 2008. Another problem, Hawks pointed out, was that scientists were preferentially choosing larger skulls to include in H. capensis while ignoring smaller skulls that were found in association with the bigger specimens. Today, fossils once classified as H. capensis are considered members of H. sapiens.
Homo rhodesiensis: If you have heard of any of the species on this list, it’s probably this one. Paleontologist Arthur Smith Woodward created the name H. rhodesiensis for a skull discovered in 1921 at Broken Hill, or Kabwe, in Zambia (once part of Northern Rhodesia). The fossil’s thick skull, sloped forehead and giant brow ridges made the species distinct from living people. Other robust African fossils dating to around 300,000 to 125,000 years ago were added to the species. However, this group of fossils has been known by many other names. Some anthropologists, for example, think the bones belong to early, more archaic members of our own species, H. sapiens. However, most researchers today lump H. rhodesiensis fossils with the more widespread species Homo heidelbergensis, which lived in Africa and Eurasia starting roughly half a million years ago and may have been the common ancestor of modern humans and Neanderthals.
November 28, 2012
One of the great origin stories in the history of mammals is the rise of primates. It’s a story that scientists are still trying to write.
In the early 20th century, anatomists believed primates—united by big brains, grasping hands and feet, and excellent vision, among other features—evolved in response to living in trees. In the 1970s, however, biological anthropologist Matt Cartmill realized an arboreal lifestyle alone wasn’t enough to explain primates’ unique set of characteristics. Plenty of mammals, like chipmunks, live in trees but don’t have nimble hands or closely spaced, forward-facing eyes that allow for good depth perception. Instead, Cartmill suggested these features evolved because early primates were insect predators. He noted that many modern predators, such as cats and owls, have forward-facing eyes because they rely on good vision to grab prey. In the case of early primates, Cartmill said, they hunted tree-dwelling insects.
Not long after Cartmill presented his explanation of primates’ roots, other researchers came up with an alternative idea: Primates evolved in step with the spread of flowering plants. Rather than relying on good vision and dexterity to nab bugs, early primates used these traits to carefully walk out to the ends of delicate tree branches to gather fruits and flowers, as well as the insects that pollinated flowering plants.
Physical anthropologists Robert Sussman and D. Tab Rasmussen of Washington University and botanist Peter Raven of the Missouri Botanical Garden review the latest evidence in support of this hypothesis in an article published online in the American Journal of Primatology.
The team suggests that the earliest primates and their extinct close relatives, a group called plesiadapiforms, weren’t strictly insect eaters and therefore the insect predation hypothesis doesn’t hold up. They point out that the molars of plesiadapiforms are rounder than the teeth of earlier mammals, which were sharp for puncturing bugs. The flatter teeth indicate plesiadapiforms were probably grinding fruits, nuts and other plant parts.
The switch to a plant diet coincides with the rise of rise of flowering plants. The earliest flowering plants show up in the fossil record roughly 130 million years ago and became the dominant type of forest plant by about 90 million years ago. Around 56 million years ago, global temperatures spiked and tropical forests spread around the world. About this time, many species of birds and bats emerged. Primates also diversified during this period. Sussman and his colleagues argue that while birds and bats could fly to the ends of branches to consume meals of fruit and nectar, primates took a different route, evolving adaptations that enabled them to be better climbers.
The skeleton of a 56-million-year-old plesiadapiform found in Wyoming provides further evidence of this scenario, the researchers say. Much of the early primate and plesiadapiform fossil record consists of teeth, but in 2002, scientists reported the discovery of the skull, hands and feet of Carpolestes simpsoni. The bones reveal that the species was a good grasper, with an opposable big toe and nails instead of claws. And the teeth indicate the creature ate fruit. But unlike living primates, C. simpsoni did not have forward-facing eyes, suggesting it didn’t have good depth perception. This is an important finding, Sussman and colleagues say. If primates evolved their characteristic features because they were visual predators, then you’d expect good vision to evolve in concert with good grasping. Instead, the C. simpsoni fossils suggest enhanced vision came later. Forward-facing eyes may have later evolved because it helped primates see through the cluttered, leafy environment of the forest canopy.
The team’s arguments rest heavily on evidence from plesiadapiforms. In the past, anthropologists have debated plesiadapiforms close connection to primates. However, Sussman and colleagues think the fossil evidence suggests the two groups shared a common ancestor, and thus the evolutionary trends seen in plesiadapiforms serve as a good guide for what happened in primates.
November 19, 2012
Lucy and Ardi are the poster children of human evolution. But these famous fossil skeletons may never have been found if it weren’t for Louis and Mary Leakey’s pioneering efforts. The pair made several discoveries at Tanzania’s Olduvai Gorge in the 1950s and 1960s that inspired other anthropologists to come to East Africa in search of human ancestors. Here’s a look at some of the most important hominid fossil finds from Tanzania.
The Nutcracker Man (OH 5): The Leakeys’ first major discovery at Olduvai Gorge occurred in 1959. Mary found the roughly 1.8-million-year-old skull of a hominid with a flat face, gigantic teeth, a large crest on the top of its head (where chewing muscles attached) and a relatively small brain. They named the species Zinjanthropus boisei (now known as Paranthropus boisei). Nicknamed the Nutcracker Man, the species was too different from modern people to be the direct human ancestor that Louis had been hoping to find. But the discovery captured public interest in human evolution, and the Leakeys went on to unearth many more hominid fossils at Olduvai. OH 5 is the fossil’s official catalog name, meaning Olduvai Hominid Number 5.
Johnny’s Child (OH 7): The next big Leaky discovery came in 1960. Mary and Louis’ son, Johnny, found a lower jaw about 300 yards away from where the Nutcracker Man was discovered. The bone came from a young hominid; thus, the fossil was nicknamed Johnny’s Child. At the same spot, the Leakeys also dug up some hand bones and skull fragments. Using these skull fragments, the Leakeys and their colleagues estimated the roughly 1.8-million-year-old hominid’s brain size: 680 cubic centimeters. That was significantly bigger than the size of the average australopithecine brain, about 500 cubic centimeters. The hand bones revealed that the hominid had a “precision grip,” when a fingertip presses against the tip of the thumb. This movement allows for fine manipulation of objects, such as turning a key in a door or threading a needle. The precision grip led the Leakeys to conclude that this hominid was the one who made the stone tools found at Olduvai. Because of the tool-making and the big brain, the Leakeys decided OH 7 represented the earliest member of the genus Homo: Homo habilis (meaning Handy Man).
OH 8: Also in 1960, the Leakeys’ team discovered a well-preserved fossil foot belonging to H. habilis. The bones indicate the hominid had modern-looking foot arches, suggesting the species walked like modern people do. Tooth marks on the specimen’s ankle reveal the hominid had been a crocodile’s lunch.
OH 9: At the same time the Leakeys unearthed the first examples of H. habilis, they also recovered the skull cap of a more recent hominid dating to about 1.4 million years ago. At 1,000 cubic centimeters, the specimen’s brain was much bigger than that of H. habilis. The skull had thick brow ridges and a low, sloped forehead—key features linking the fossil to the species Homo erectus.
Twiggy (OH 24): Discovered in 1968 by Peter Nzube, Twiggy is a skull belonging to an adult H. habilis dating to roughly 1.8 million years ago. Although OH 24 is the most complete H. habilis skull from Olduvai Gorge, it was found crushed completely flat (and therefore named after the slender British model of the same name). Paleoanthropologist Ron Clarke reconstructed what the skull would have looked like, but it’s still fairly distorted.
LH 4: In the 1970s, after Louis died, Mary began excavations at Laetoli, about 30 miles from Olduvai Gorge. The fossils she was finding there were much older than the bones she and Louis had discovered at Olduvai. In 1974, for example, her team unearthed a lower jaw with teeth dating to 3.6 million years ago. It was cataloged as Laetoli Homind 4, or LH 4. Around the same time, anthropologists at the site of Hadar in Ethiopia were also finding hominid fossils dating to more than 3 million years ago, including the famous Lucy skeleton. At first, no one was sure what to call these older fossils. After analyzing both the Hadar and Laetoli specimens, anthropologists Tim White and Donald Johanson (Lucy’s discoverer) concluded that all of the fossils represented one species that they called Australopithecus afarensis. They chose LH 4 as the species’ type specimen, or the standard representative of the species. Mary did not approve. She didn’t believe the fossils from Laetoli were australopithecines. But under the rules of taxonomy, once a type specimen is designated, it’s forever associated with its species name. (For more on the controversy, see Johanson’s book Lucy.)
Laetoli Footprints: In 1978, one of Mary’s team members, Paul Abell, made the most famous discovery at Laetoli: He found the trail of about 70 fossilized hominid footprints. Based on the footprints’ age, 3.6 million years, anthropologists think they were made by an A. afarensis group. The footprints reveal this early hominid had a very modern way of walking. The big toe was in line with the other toes, not off to the side like an ape’s big toe. And the prints reveal the walkers had arches, unlike the flat feet of an ape. The footprints also suggest A. afarensis had a modern gait.
October 10, 2012
Ethiopia may well deserve the title Cradle of Humankind. Some of the most famous, most iconic hominid fossils have been discovered within the country’s borders. Ethiopia can claim many “firsts” in the hominid record book, including first stone tools and the first Homo sapiens. Here’s a look at the country’s most important hominid finds.
Omo I and II (1967-1974): While excavating the Kibish Formation near the Omo River, Richard Leakey and his colleagues uncovered a partial skull and skeleton (Omo I) and a partial skull (Omo II) that are still thought to be the oldest examples of Homo sapiens. Dating to 195,000 years ago, Omo I has several features that clearly place it within our species, including a flat face, high forehead and prominent chin. Omo II, on the other hand, looks more primitive. While some researchers suggest its thicker skull and sloped forehead preclude it from being a true modern human, others say those features were probably within the range of variation for early H. sapiens.
Lucy (1974): While searching a dry gully at the site of Hadar, paleoanthropologist Don Johanson noticed a slender arm bone sticking up from the ground. He thought it belonged to a hominid. Then he noticed a thigh bone, some bits of a spine, a pelvis and some ribs. Eventually, Johanson and his colleagues unearthed approximately 40 percent of a hominid skeleton dating to roughly 3.2 million years ago. Named Lucy after the Beatles’ “Lucy in the Sky with Diamonds,” the skeleton is officially known as AL 288-1 and is arguably the most famous hominid fossil ever found. But it took a while for Johanson, with the help of paleoanthropologist Tim White, to figure out what Lucy was—Australopithecus afarensis—and her place in the human family tree. (For a firsthand account of Lucy’s discovery and the analysis of her remains, you probably can’t find a better book than Lucy: The Beginnings of Humankind by Johanson and Maitland Edey, even if some of the science is out of date.)
First Family (1975): Just a year after discovering Lucy, Johanson’s team got lucky again, finding a jumble of more than 200 A. afarensis fossils at the site of Hadar. The collection—representing as many as 17 individuals—was dubbed the “First Family” (official name: AL 333). Because the fossils contained both adults and youngsters, the First Family is a snapshot of variation within A. afarensis and offers a look at how an individual within the species might have grown up. Anthropologists are still trying to figure out what led to the demise of such a large group of hominids. A catastrophic flood is one theory; death by over-eager carnivores is another.
Australopithecus garhi (1990, 1996-1998): Paleoanthropologists Berhane Asfaw and Tim White found a partial skull and other pieces of the 2.5-million-year-old species known as A. garhi in 1990 at the site of Bouri. Since then, no additional fossils have been unearthed (or, at least, matched to the species). Not much is known about A. garhi. Based on the length of a thigh bone, the species may have had slightly longer legs, and therefore a longer stride, than Lucy’s kind. Given the species’ age and where it was found, A. garhi may have been the hominid to make the oldest known stone tools (described next).
Oldest Stone Tools (1992-1994): At 2.6 million years old, the stone choppers, or Oldowan tools, at the site of Gona are a few hundred thousand years older than any other known stone tool. But the Gona tools’ status as earliest stone tool technology was recently challenged by another Ethiopian discovery. In 2010, archaeologists claimed that roughly 3.39-million-year-old mammal bones from Hadar contained scratches that could have only been made by a stone tool, implying stone tools were an even earlier invention than scientists had thought. Other researchers remain unconvinced that the markings were made by hominid butchering. And since no actual stone tools were found along with the bones, the Gona artifacts’ title of earliest known stone tools is still safe.
Ardi (1992-1994): Older than Lucy, Ardi is the most complete skeleton of an early hominid. The first pieces of the 4.4-million-year-old Ardi were uncovered in 1992 by one of Tim White’s graduate students, Gen Suwa, in the Middle Awash Valley. White and his colleagues then spent more than 15 years digging Ardi out and analyzing the skeleton. The hominid did not look like Australopithecus, so the researchers gave it a new name: Ardipithecus ramidus. Although the species walked upright on two legs, its form of bipedalism was quite different from that of modern people or even Lucy. Its discoverers think Ardipithecus represents an early form of upright walking and reveals how apes went from living in the trees to walking on the ground.
Ardipithecus kadabba (1997): Yohannes Haile-Selassie of the Cleveland Museum of Natural History unearthed hand, foot and other bones in the Middle Awash Valley that looked a lot like those of Ar. ramidus—only the bones were almost a million years older, with an age of about 5.8 million years. Teeth found in 2002 suggested the more ancient hominids deserved their own species: Ar. kadabba. It remains one of the earliest known hominid species.
Dikika Child (2003): From the site of Dikika comes the fossil of an approximately 3-year-old A. afarensis child dating to 3.3 million years ago. Sometimes called Lucy’s baby or Selam, it’s the most complete skeleton of an early hominid child, including most of the skull, torso, arms and legs. The fossil’s discoverer, Zeresenay Alemseged, of the California Academy of Sciences, and colleagues say the fossils suggest A. afarensis grew up quickly like a chimpanzee but was beginning to evolve slower growth patterns like those of modern humans.
Herto fossils (2003): Even if the Omo I and II fossils turned out not to be members of H. sapiens, Ethiopia would still be home to the earliest known members of our species. A team led by Tim White discovered three 160,000-year-old skulls in the Middle Awash Valley. Two belonged to adult H. sapiens while the other was of a child. Due to some features not seen in modern populations of humans, White and his colleagues gave the skulls their own subspecies: H. sapiens idaltu.
Australopithecus anamensis (2006): A. anamensis, the earliest species of Australopithecus, was already known from Kenya when a team led by Tim White of the University of California, Berkeley discovered more fossils of the species further north in Ethiopia’s Middle Awash Valley. The collection of roughly 4.2-million-year-old fossils is notable because it includes the largest hominid canine tooth ever found and the earliest Australopithecus femur.