November 7, 2012
The bow and arrow is an ancient weapon—going back at least 71,000 years, a study published in Nature suggests. Archaeologists working at South Africa’s Pinnacle Point cave site uncovered a collection of tiny blades, about an inch big, that resemble arrow points, likely belonging to prehistoric bow and arrows or spear-throwers. The researchers say the discovery is further evidence that humans (Homo sapiens) started to act and think like modern people early in their evolution.
The skeletons of H. sapiens appear in the fossil record by about 200,000 years ago in Africa. But when modern culture and cognition emerged is still an open question. Some anthropologists think the human brain evolved in tandem with the rest of the body, and culture built up slowly over time as technology advanced. Others have suggested there was a disconnect between physical and behavioral modernity, with some sort of genetic mutation roughly 40,000 years ago causing an abrupt change in how humans think. Still other researchers argue that incipient signs of advanced intellect appear early in the archaeological record but then disappear for thousands of years before reappearing. Needless to say, there’s a lot of debate on this subject. (For a detailed discussion on the topic, check out the story I wrote in June for Smithsonian.com).
Kyle Brown of the University of Cape Town and his colleagues say the tiny blades that they found are signs of complex tool making. The tiny tools were created from silcrete stone that people had heated over a fire to make the raw material easier to work with before chipping the rock into blades. This suggests people had to follow a lengthy multi-step process to make the blades, which included gathering the stones, gathering fuel for the fire, heating the rocks and carefully cutting the stone into delicate blades. The shape of the blades looks like the shape of arrow tips found in more recent arrows, which led Brown and colleagues to conclude the blades were used in bow-and-arrow projectile weapons. That implies there were even more steps in the tool-making process, such as hafting the stone tips to a wooden shaft.
The blades aren’t the only evidence that humans had advanced cognitive abilities as early as 71,000 years ago. Pigments, jewelry and other art found in South African cave sites dating to as many as 164,000 years ago suggest that early humans were capable of abstract or symbolic thinking. Some researchers view this ability as central to human intellect.
The new study, however, goes one step further. The researchers say the blades were found throughout a geological section of Pinnacle Point that spans roughly 11,000 years (71,000 to 60,000 years ago), indicating people could communicate complicated instructions to build intricate tools across hundreds of generations. This instance of long-term maintenance of a cultural tradition early in human history is evidence that the capacity for modern culture began early and slowly built up, Brown and colleagues say. Previous suggestions that complex culture came and went in the early days of humans is probably an artificial result, they say, because so few African sites have yet been excavated.
November 5, 2012
If you’re on the shorter end of the height spectrum, you know how frustrating it can be to take a stroll with someone who’s tall. At times, you might have to remind your companion to slow down, that your shorter legs can’t keep up. This might have been an even bigger problem for our famous ancestor, Lucy. Within the species Australopithecus afarensis, there was considerable variability in height and limb length, and different members of the species may have had vastly different preferences for walking speeds, new research suggests. How did our ancestors cope with such a dilemma?
The problem really became apparent in 2010 with the discovery of a partial A. afarensis skeleton, nicknamed “Big Man,” in Ethiopia. As his name suggests, the five-foot-tall Big Man was big, at least for an early hominid, and compared to the three-and-a-half-foot-tall Lucy. Big Man’s shin, for instance, was about 50 percent longer than that of Lucy’s—the sort of length difference you see today between a six-year-old child and a six-foot-tall man. But in Lucy and Big Man’s case, both individuals were adults, suggesting there was a large range of heights for A. afarensis. The variation might have been related to sex, with males being significantly taller than females. Or there might have been regional differences in A. afarensis size. Lucy and Big Man were both found in Ethiopia but at different sites.
To understand the walking behavior of Lucy, Big Man and their kind, Patricia Ann Kramer of the University of Washington in Seattle did some experiments with people. In modern humans, the length of the lower leg (or tibia) plays a big role in how much energy a person expends while walking and what his/her preferred speed is. Kramer examined this relationship by measuring the tibia length of 36 children and 16 adults and then placing the volunteers on treadmills to record how much energy they used (measured in terms of oxygen consumption) while walking at different speeds. She discovered that, in general, individuals with longer lower legs have higher “optimal velocities.” That means the speed at which longer-legged people consume the least amount of energy is faster than that of shorter-legged people.
Kramer used the data to create a mathematical equation that related leg length to speed to estimate Lucy’s and Big Man’s optimal velocities based on their tibia lengths. Lucy’s would have been 1.04 meters per second (about 3.4 feet per second) while Big Man’s would have been as much as 1.33 meters per second (about 4.4 feet per second). To put this in perspective, if both individuals walked for an hour at their optimal speeds, Lucy would have covered 3.74 kilometers (2.3 miles) while Big Man would have traversed 4.68 kilometers (2.9 miles), Kramer reports in the American Journal of Physical Anthropology.
Based on two individuals, it’s hard to say how representative these results are for A. afarensis. And even assuming there were big differences in walking speeds, it’s hard to say how it would have affected the behavior of these early hominids. If size differences were sex based, then some members of a group might have had to compromise their preferred walking speed—perhaps females had to walk faster (and thus expend more energy) to keep up with males or maybe males slowed down (also expending more energy) to appease females or maybe both sexes had to adjust their velocities. Another possibility is that males and females spent time away from each other during the day, Kramer says. Among wild chimpanzees, males and females often range separately while searching for food, which might be a consequence of different walking speeds. More studies that examine sex-based ranging patterns in primates might offer more clues to how A. afarensis could have coped. Of course, this variation in height might not have been a problem at all if differences were largely regional.
Although Kramer’s work doesn’t provide any definite answers, it highlights how difficult it is to reconstruct the biology and behavior or our ancestors. It’s clear that A. afarensis walked upright, but we still have a lot to learn about how the early hominid traveled across the East African landscape.
October 31, 2012
Finding the earliest primates isn’t easy. The first members or our order probably lived about 65 million years ago and were rat-sized critters known mainly from teeth. With such scant evidence, researchers have had a hard time classifying these creatures and making connections to modern primates. Still, scientists have identified dozens of early primate, or probable primate, species. If you’re unfamiliar with our earliest origins, here are five primates to know.
Purgatorius: Discovered at Montana’s Hell Creek Formation, this shrew-sized mammal lived roughly 65 million years ago at the end of the Cretaceous period. Purgatorius‘ place in the primate family tree is debated. Aspects of the genus’ teeth align it with a group of extinct, primate-like mammals called plesiadapiforms. Some scientists say that the number and variety of teeth Purgatorius had makes it a possible common ancestor to primates and plesiadapiforms. Last week, paleontologists from Yale University announced they found the first known Purgatorius ankle bones. The researchers say the fossils reveal the animal had flexible feet like modern tree-living mammals do, implying the earliest primates were indeed arboreal animals as scientists suspected.
Altiatlasius: A few molars and a jaw fragment are all that’s known of this small mammal discovered in Morocco. Many paleontologists consider Altiatlasius, which lived some 57 or 56 million years ago, to be the first true primate. How the ancient primate relates to modern primate lineages is unclear. While some researchers believe it’s similar to a group of primitive tarsier-like primates, others think it might be an ancient forefather of monkeys and apes.
Teilhardina: Named for the French paleontologist Pierre Teilhard de Chardin, Teilhardina has been found at North American and Asian sites dating to almost 56 million years ago. Scientists group the genus with the omomyids, a family of tarsier-like primates that emerged during the Eocene epoch some 56 million to 34 million years ago. Last year, scientists reported they had unearthed a cache of Teilhardina fossils in Wyoming’s Big Horn Basin that included the first evidence that early primates had nails instead of claws. The tips of the animal’s finger and toe bones were flattened, indicating the presence of fingernails, the researchers reported in the American Journal of Physical Anthropology.
Notharctus: This North American genus lived about 50 million years ago and belonged to a family of lemur-like primates called adapiforms. Notharctus had a long tail, leaped from tree to tree and snacked on leaves. A report published in PLOS ONE in January described fossils from this primate that indicate it would have had something like a cross between a fingernail and a claw on its second toe—kind of like modern lemurs, lorises and bush babies (or galagos) that all have a “grooming” claw on their second toe. But it’s not yet clear whether Notharctus was on its way towards evolving a true grooming claw, or on its way towards evolving a true nail.
Eosimias: Discovered in China, Eosimias lived about 45 million years ago. The size and shape of its teeth suggest it was the earliest ancestor of the lineage leading to monkeys and apes (and us!). Fossils of its feet suggest Eosimias walked on all fours like a modern monkey.
October 29, 2012
I’m a primate. You’re a primate. Everyone reading this blog is a primate. That’s not news. We hear it all he time: Humans are primates. But what does that really mean? What do we have in common with a baboon? Or a creepy aye-aye? Or even our closest living relative, the chimpanzee?
These are simple questions to answer from a genetic perspective—humans share more DNA with lemurs, monkeys and apes than they do with other mammals. Genetic research of the last few decades suggests that humans and all living primates evolved from a common ancestor that split from the rest of the mammals at least 65 million years ago. But even before DNA analyses, scientists knew humans belong in the primate order. Carl Linnaeus classified humans with monkeys, apes and other primates in his 18th-century taxonomic system. Even the ancient Greeks recognized similarities between people and primates. Today, anthropologists recognize several physical and behavioral traits that tie humans to primates.
First, primates have excellent vision. They have forward-facing eyes that sit close together, which allows the eyes’ fields of view to overlap and create stereoscopic, or 3-D, vision. (In contrast, for example, a cow or giraffe has widely spaced eyes and therefore poor depth perception.) Related to this great eyesight is the presence of a post-orbital bar, a ring of bone that surrounds the eyeball. Many primates also have a completely bony socket that encloses the eye. This bone probably protects the eye from contractions of chewing muscles that run down the side of the face, from the jaw to the top of the head. Many mammals that rely less on vision don’t have a post-orbital bar. If you poked a dog in the side of its head near the temple, you would feel muscle and the eye but no bone (and you would probably be bitten, so please don’t do that). Because primates depend on their vision so much, they generally have a reduced sense of smell relative to other mammals.
Primates are also very dexterous. They can manipulate objects with great skill because they have opposable thumbs and/or big toes, tactile finger pads and nails instead of claws (although some primates have evolved so-called grooming claws on some of their toes). Primates also generally have five fingers/toes on each hand/foot. This is actually a very ancient trait. The earliest mammals had five digits, and over time, many mammalian lineages lost a few fingers and toes while primates kept all of them. Primates also retain collar bones, which allow for greater mobility in the shoulder; mammals that strictly walk on all fours, such as horses, lack collar bones so their limbs are more stable and don’t slip to the side while running.
And in general, primates tend to have larger brains than other mammals of a similar size. They also have smaller litters—often just one baby at a time—and longer periods of gestation and childhood.
Scientists are still trying to understand why primates’ unique set of features evolved. Some researchers think the earliest primates lived in trees, so good vision and dexterity would have been helpful in judging distances between branches or for climbing around. Others, such as Boston University’s Matt Cartmill, have suggested that these traits emerged because early primates might have been insect predators and needed clear eyesight and quick hands to grab prey. Both factors, as well as many others, could have played a role.
October 25, 2012
The most famous Australopithecus afarensis skeleton is named for the Beatles’ “Lucy in the Sky with Diamonds.” But a better anthem for the species might be “Lucy in the Trees with Chimpanzees.” A new study investigating how A. afarensis‘ shoulders grew during childhood indicate the early hominid spent at least some of its time climbing in trees. The work, published online today in Science, adds another bit of evidence to a decades-long debate about how Lucy and her kind traveled through their environment.
There’s no question that A. afarensis, which lived about 3.85 million to 2.95 million years ago, walked upright on two legs. The species possessed numerous physical features associated with bipedalism, such as thighs that angled in toward the knees and arched feet that lacked the grasping big toes seen in tree-climbing apes. But the hominid also had characteristics that are normally found in arboreal apes, such as curved fingers and toes, which are useful for gripping tree limbs. So the controversial question has been: Did A. afarensis actually climb trees? Or were the so-called climbing traits just evolutionary holdovers that the species didn’t use but hadn’t lost yet?
The new study takes a novel route in addressing these questions, looking at the development of the shoulder blades in A. afarensis. David Green of Midwestern University in Downers Grove, Illinois, and Zeresenay Alemseged of the California Academy of Sciences began by carefully liberating the left and right shoulder blades from the block of rock holding together the Dikika Child, a 3-year-old A. afarensis that lived about 3.3 million years ago. The fossil was unearthed in Ethiopia between 2000 and 2003, and it’s taken this long to remove the delicate shoulder blades, which are a rare find in the hominid fossil record.
The pair compared the Dikika Child’s shoulder bones with those of a few adult A. afarensis specimens, as well as those of juvenile and adult shoulders from other Australopithecus species, Homo erectus, modern humans and modern apes. By comparing children to adults, the researchers could assess how the size and shape of the shoulder blade changed as a young A. afarensis grew up. In chimpanzees and gorillas, the shoulder blade develops in a characteristic way because frequent climbing during childhood affects how the shoulder grows—in other words, the apes’ shoulders change as a result of climbing. The shoulders of modern humans and H. erectus look very different and have their own growth trajectory because neither species spends any significant time climbing during childhood and adolescence (playing on “monkey” bars doesn’t count). In the new research, Green and Alemseged conclude the shoulder of A. afarensis developed in the same manner as an African ape’s, indicating the early hominid must have spent at least some time climbing in trees.
That doesn’t mean swinging through the treetops was A. afarensis‘ preferred mode of locomotion. In the past, paleoanthropologists have suggested that Lucy’s small size (she was no bigger than a chimp) made her vulnerable to leopards and other hungry predators. So while the hominid might have spent most of its time walking upright on the ground, at night it might have taken shelter in trees—perhaps making a nest as many chimpanzees do.