December 3, 2012
It can be hard to find gifts for lovers of human evolution. They aren’t as easy to find as, say, dinosaur gifts. So I spent some time cruising the Internet looking for some unusual and unique options for the holidays this year. Here’s what I found.
Something to read:
Over the last year, several books on how modern humans took over the world were published. Lone Survivors by anthropologist Chris Stringer weaves archaeology with genetics to explain why Homo sapiens became the last hominid left on Earth. The Last Lost World by father-and-daughter duo Stephen and Lydia Pyne considers how hominids evolved during the ice ages of the Pleistocene epoch and how scientists’ understanding of this period, lasting some 2.6 million to 11,700 years ago, has changed over time. Anthropologist Ian Tattersall takes an even broader look at the rise of humans, surveying the last 8 million years or so of human evolution in Masters of the Planet. In Homo Mysterious psychologist David Barash examines a number of evolutionary puzzles, including why humans have big brains and why women tend to live longer than men.
If you’re shopping for an uber-hominid fan, consider this simple “I Heart Hominids” bumper sticker, or maybe human evolution decals to jazz up a boring lapotop. I’m hoping for a hominid skull to put in my office: made out of chalkboard, they come in various species and colors. Candle lovers might be intrigued by this unusual candle holder. And who wouldn’t want a Neanderthal piñata?
Some hominid gifts can be fun and practical. Need a bag to carry groceries? How about this “I Love Lucy” cotton tote with a picture of the Lucy skeleton. It comes in several different sizes. Or maybe your loved one would like a pewter key chain of a Paranthropus boisei or Homo erectus skull, which a reader of last year’s Hominid Hunting holiday gift guide suggested. These colorful glass coasters are also useful.
Something to hang on the wall:
I think I’ve said this before–the Taung Child is my favorite hominid fossil. If you know someone else who really digs the specimen, check out this framed drawing of the skull. These woodcut prints of hominid skulls are another good way to spruce up an empty wall. A Bigfoot skeptic (or a believer with a sense of humor) might like this print from Society 6.
Last year, the big ticket items in my gift guide were hominid fossil reproductions. This year, you can give someone his/her genome. With only a sample of saliva, the genetics company 23andMe analyzes an individual’s complete set of DNA to trace the geographic origins of that person’s forefathers and to look for Neanderthal ancestry.
What would you like for the holidays?
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 26, 2012
Humans and Neanderthals split from a common ancestor roughly half a million years ago. While many anthropologists will tell you we don’t really know who that common ancestor was, others will say we do: the species Homo heidelbergensis, or something very much like it. An even smaller portion will point to another possibility: a controversial species called Homo antecessor.
H. antecessor, which first came to light in the 1990s, is known almost entirely from one cave in northern Spain’s Atapuerca Mountains. While working at the Gran Dolina site from 1994 to 1996, a team of Spanish researchers found 80 fossils belonging to six hominid individuals that lived roughly 800,000 years ago. The hominids’ teeth were primitive like those of Homo erectus, but aspects of the hominid’s face—particularly the shape of the nasal region and the presence of a facial depression above the canine tooth called the canine fossa—were modern, resembling features of modern people. The unique mix of modern and primitive traits led the researchers to deem the fossils a new species, H. antecessor, in 1997.
In 2008, the researchers expanded the timeline of the species . At another cave site in Atapuerca, Sima del Elefante, scientists unearthed a partial lower jaw, as well as a few dozen stone tools, dating to about 1.2 million years ago. Outside of Spain, the only other potential evidence of H. antessor
fossils are stone tools found at a nearly 800,000-year-old English archaeological site named Happisburgh that might have been made by the species.
H. antessor‘s discoverers—including José Bermúdez de Castro of Spain’s National Museum of Natural Sciences, Juan Luis Arsuaga of the Universidad Complutense in Madrid and Eudald Carbonell of the University of Tarragona—say the species’ similarities with modern people, and its age, make it the best known candidate for the common ancestor of Neanderthals and Homo sapiens. They suggest H. antecessor may have evolved from a population of H. erectus living in Africa more than 1.5 million years ago and then migrated to Europe, journalist Ann Gibbons reported in Science when H. antecessor was first announced. Although the species has yet to be discovered in Africa, an African origin for H. antecessor may be necessary if it was indeed the direct ancestor of modern humans, which all fossil evidence suggests originated in Africa. Furthermore, the researchers say H. heidelbergensis is too similar to Neanderthals to be a direct ancestor of modern humans. Instead, H. antecessor gave rise to H. heidelbergensis, which then gave rise to Neanderthals.
But many anthropologists are not on board with this scenario. One problem is that most of the known H. antecessor specimens represent children, Gibbons reported. Only two of the six individuals found at Gran Dolina are thought to be adults, about 20 years old. Since most of the features tying H. antecessor to modern people were found in juveniles—whose bodies and physical features change as they grow up and go through puberty—it’s possible that H. antecessor adults didn’t really look much like H. sapiens at all. And if that’s the case, then it’s hard to argue the species had an ancestor-descendent relationship with us. The issue won’t be settled until researchers find good examples of complete adult H. antecessor fossils.
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.
November 14, 2012
The nearly 2-million-year-old Paranthropus boisei was the cow of the hominid family. Unlike other human cousins, the species was a fan of dining on grasses. But it turns out it wasn’t the only, or even the first, hominid grazer. Australopithecus bahrelghazali was munching on grasses and sedges at least 1.5 million years before the origin of P. boisei, a new study in the Proceedings of the National Academy of Sciences suggests. The findings may mean early hominids were capable of consuming a wide variety of foods and colonizing new environments.
But before we discuss how scientists figured out A. bahrelghazali‘s diet, and why that matters, we need to address a far more pressing question: Who the heck was A. bahrelghazali?
In 1993, researchers in Chad unearthed a 3.5-million-year-old hominid lower jaw fragment and a few attached teeth. Based on the fossils’ age, many paleoanthropologists think the bones belonged to Australopithecus afarensis. But the specimen was found more than 1,500 miles farther west than any other A. afarensis bones, and subtle differences in the size and shape of the fossils led the discoverers to conclude they had found a new species. They named it A. bahrelghazali after the Bahr el Ghazal valley in Chad where the bones were recovered. Since then, researchers haven’t found any other A. bahrelghazali fossils and its species’ status remains controversial.
With just a jaw and teeth, there’s not too much scientists can say about what A. bahrelghazali looked like or how it lived its life. But, fortunately, diet is something that can be gleamed from these fossils. Analyzing the teeth’s chemistry is one way to assess what the species ate. This is possible because the carbon found in plants comes in two versions, or isotopes, called C3 and C4. Trees and other forest plants are rich in C3; grasses, sedges and other grassland plants have an abundance of C4. When an animal eats these plants—or eats other animals that eat these plants—the different carbon isotopes get incorporated into the individual’s teeth, serving as a record of what it once ate. Previous work on P. boisei has shown that C4 plants made up as much as 77 percent of that hominid’s diet.
In the new study, Julia Lee-Thorp of Oxford University and colleagues come to a similar conclusion for A. bahrelghazali, that the species mainly ate C4 plants, probably grasses and sedges. And like modern baboons that live on savannas, the hominid probably ate different parts of these plants, including underground tubers and bulbs. This diet is not surprising given the type of habitat A. bahrelghazali lived in. Based on the other types of animals found near the hominid, the researchers say A. bahrelghazali made its home in an open grassland, with few trees, near a lake. So forest foods weren’t really a dining option.
The results mean that by 3.5 million years ago hominids were probably already “broad generalists” capable of eating a variety of foods depending on what was locally available, the researchers say. (The younger Australopithecus sediba,which lived roughly 2 million years ago, demonstrates some of the stranger foods that hominids could eat: The South African species liked to eat wood—a dietary preference not seen in any other hominid.) Being a food generalist may have allowed A. bahrelghazali to explore new environments and leave behind the forests that earlier hominids, such as Ardipithecus ramidus, and their ancestors resided in.