October 15, 2012
I was sick this weekend. The kind of sick where your nose runs so much that you begin to question how the human body can produce so much mucus. My throat hurt. I was coughing. But the worst part was the headache: My head felt like it was being continuously squeezed by a vise, or maybe some sort of medieval torture device. The pain was so bad even my teeth hurt. As I was lying in bed next to my half-empty box of Kleenex, I thought, “This wouldn’t be happening if we had descended from Asian, not African, apes.” (Yes, I was really thinking that.)
But before I explain what apes have to do with my cold, let’s cover some basic biology. When the cold virus (or bacteria or an allergen like ragweed) enters the body, the nose produces mucus to prevent an infection from spreading to the lungs. This results in a runny nose. All of the extra snot can also plug up passages that connect the nose to air-filled pockets in the bones of the skull, called sinuses. Sinuses produce their own mucus and are thought to help humidify air, as well as stabilize and strengthen the skull. But when the passageways between the head’s sinuses and nasal cavity get blocked, the sinuses’ mucus can’t drain and the air pockets fill, causing pressure to build . Sometimes the lining of the sinuses swell, which results in the further production of mucus and build-up of pressure. That pressure hurts.
Humans have four types of sinuses that play a role in sinus headaches: the frontal sinus in the forehead, the maxillary sinus in the cheeks, the ethmoid sinus between the eyes and the sphenoid sinus behind the nose. The African apes, gorillas and chimpanzees, have all four of these sinuses. The Asian apes, orangutans and gibbons (the so-called lesser apes because of their smaller size), have just two, lacking the ethmoid and frontal sinuses.
The ethmoid and frontal sinuses can be traced back at least 33 million years ago to a primate called Aegyptopithecus that lived in Africa before the ape and Old World monkey lineages originated. (Old World monkeys are those that live in Africa and Asia.) These sinuses have also been found in some of the earliest known apes, such as the roughly 20-million-year-old Morotopithecus and 18-million-year-old Afropithecus, both from Africa. Chimpanzees, gorillas and humans inherited these sinuses from the most ancient apes. Gibbons and orangutans, however, each lost these sinuses independently after they diverged from the rest of the apes; gibbons evolved about 18 million years ago while orangutans split from the other great apes roughly 15 million years ago.
It’s not clear why the Asian apes lost the ethmoid and frontal sinuses. In the case of the orangutan, the animal has a much more narrow space between its eyes and a more severely sloped, concave forehead than the African great apes. So there just may not be room for these air pockets to form.
But gibbons and orangutans do still have the maxillary and sphenoid sinuses, which are enough to cause annoying pain and headaches. So I should really apologize to my African ape ancestors. Clearly, I had some misdirected anger. I should have been mad at the virus that invaded my body.
September 17, 2012
Why hominids evolved upright walking is one of the biggest questions in human evolution. One school of thought suggests that bipedalism was the most energetically efficient way for our ancestors to travel as grasslands expanded and forests shrank across Africa some five million to seven million years ago. A new study in the Journal of Human Evolution challenges that claim, concluding that the efficiency of human walking and running is not so different from other mammals.
Physiologists Lewis Halsey of the University of Roehampton in England and Craig White of the University of Queensland in Australia compared the efficiency of human locomotion to that of 80 species of mammals, including monkeys, rodents, horses, bears and elephants. For each species, Halsey and White computed the “net cost of transport,” a figure that considers an animal’s metabolic rate (measured in oxygen consumption), given its speed, while traveling one meter. Next, they created an equation that predicts a mammal’s net cost of transport based on its body mass.
The researchers found that a typical mammal weighing 140 pounds (the average weight for humans) has a net cost of transport of 10.03 milliliters of oxygen per meter while running. Human running on average requires 12.77 milliliters of oxygen per meter—27 percent more than the researchers’ calculation. In contrast, human walking is 25 percent more efficient than the average, same-sized mammal’s walking. The team also estimated that the roughly three-million-year-old Australopithecus afarensis‘ walking was 26 to 37 percent more efficient than the average mammal’s, depending on the estimated weight of the chimp-sized hominid.
Although modern humans and A. afarensis are more efficient walkers than the average mammal, Halsey and White argue that neither species is exceptional. When looking at all of the data points, both hominids fall within the 95 percent prediction interval for mammals. Statistically speaking, that’s the range you’d expect 95 percent of predicted mammalian net transport costs to fall within on average. In other words, modern humans and A. afarensis fall within the normal realm of variation for mammals. There’s nothing special about the energetics of their walking, Halsey and White conclude.
To evaluate whether energy efficiency played a role in the evolution of upright walking, Halsey and White note that hominids should be compared to their closest relatives. For example, if human walking is more efficient than chimpanzee walking than you would expect based on chance alone, then it lends support to the energy-efficiency explanation. But that’s not what the researchers found. In fact, the energetic differences between humans and chimpanzees are smaller than the differences between very closely related species that share the same type of locomotion, such as red deer versus reindeer or African dogs versus Arctic foxes. In some cases, even different species within the same genus, such as different types of chipmunks, have greater variation in their walking efficiencies than humans and chimps do. The researchers speculate that factors like climate and habitat might explain why such similar animals have such different locomotor costs.
This one study is unlikely to be the last word on the matter. I’m curious how the estimated energy efficiency of A. afarensis compares to chimpanzees, or even to modern humans, something the researchers didn’t examine. It would also be interesting to calculate the net transport cost for the 4.4-million-year-old Ardipithecus, the oldest hominid for which anthropologists have a complete skeleton. That seems like the crucial test of whether energy efficiency played some kind of role in the evolution of bipedalism.
September 5, 2012
The earliest known instance of cannibalism among hominids occurred roughly 800,000 years ago. The victims, mainly children, may have been eaten as part of a strategy to defend territories against neighbors, researchers report online in the Journal of Human Evolution. The new study shows how anthropologists use the behavior of modern humans and primates to make inferences about what hominids did in the past—and demonstrates the limitations of such comparisons.
The cannibalism in question was discovered in the Gran Dolina cave site of Spain’s Atapuerca Mountains. Eudald Carbonell of the University of Rovira and Virgili in Spain and colleagues found evidence of butchering on bones belonging to Homo antecessor, a controversial species that lived in Europe as early as 1.2 million years ago. Because no other hominid species has been found in the region at the same time as the butchered bones, the victims must have been eaten by their own kind, the team concluded in 2010 in the journal Current Anthropology (PDF).
Today, human cannibalism occurs in a variety of contexts: for nutritional value (often in times of starvation), as part of funerary rituals or during warfare. The different purposes of cannibalism can leave different patterns in the archaeological record. When humans consume other humans for purely dietary reasons, the victims are often treated just like any other prey. This is what the researchers found at Gran Dolina. Eleven individuals were butchered in a manner similar to that of deer and other mammals: Bones had cut marks in areas of muscle attachments and the skulls had signs of defleshing. Thus, H. antecessor appeared to eat its own kind for a nutritional purpose—but probably not because of a food shortage, as the team says there’s evidence of cannibalism over an extended period of time, dozens or even hundreds of years.
So why cannibalism? To find an answer, the researchers looked to chimpanzees. That’s because some aspects of H. antecessor cannibalism don’t resemble those of contemporary human cannibalism or cannibalism seen in Neanderthals or early modern humans living 100,000 years ago. For instance, nine of the 11 butchered individuals at Gran Dolina were children or adolescents compared with the largely adult victims of more recent human cannibalism.
Young victims is a pattern seen among chimpanzees. When female chimps range alone near the boundary of their territory, males from the neighboring group may kill and eat the females’ infants. Carbonell and his colleagues suggest the best explanation for this behavior is territorial defense and expansion. Males may attack to scare off other chimps as a way to protect their resources and gain new land to roam; such attacks are easiest against vulnerable females and their young, which make good meals. The team likewise concludes a similar explanation may have been the motivation behind H. antecessor cannibalism.
Whether this is a reasonable conclusion depends on some unanswered questions. For example, the researchers assume that the cannibalism was the result of intergroup violence and aggression, but they offer no evidence that the H. antecessor cannibals came from a different group than the victims. If they were all members of the same clan, then territorial defense doesn’t seem likely. It also seems unlikely if H. antecessor‘s social structure was vastly different from chimps—in which groups of probably related males band together to actively defend a territory while females in a community often forage alone with their infants.
It looks like the team has some more work to do.
June 6, 2012
Europe is not where most people would search for the common ancestor of chimpanzees, gorillas and humans. But that’s exactly where one team of anthropologists thinks the grandfather of the African apes came from.
But before we explore the origins of African apes, it helps to know how to identify a paleo-ape in the fossil record. The most distinct physical traits that all living apes share are the ones that help the animals swing through trees: long arms; a broad, flat chest; a short, stiff lower back; and long, curved fingers and toes. They also lack a tail. These traits didn’t evolve all at once, however. The world’s earliest known ape—the 20-million-year-old Proconsul from East Africa—had a monkey-like body, but aspects of the wrist and the absence of a tail indicate Proconsul did indeed sit at the base of the ape family tree.
By about 17 million years ago, apes appear in Europe’s fossil record. In a recent issue of Evolutionary Anthropology, David Begun and Mariam Nargolwall, both of the University of Toronto, and László Kordos of the Geological Institute of Hungary describe Europe’s fossil apes and why they think Europe was, in a sense, the motherland of African apes.
The ancestors of European apes probably came from Africa as part of a wave of mammals that were attracted to the continent’s subtropical forests. During the early part of the Miocene, the epoch that spans roughly 23 million to 5 million years ago, the two land masses were connected by land bridges that crossed the ancient Tethys Sea (a more expansive version of the Mediterranean). The first European apes, which lived 17 million to 13.5 million years ago, were Griphopithecus (found in Germany and Turkey) and Austriacopithecus (found in Austria). Both apes are known mainly from teeth and jaws, so we don’t know what their bodies looked like. But they did have thick dental enamel, another ape-like characteristic.
By about 12.5 million years ago, the first apes that really resemble modern great apes emerged in Europe and Asia. Those in Asia gave rise to that continent’s sole living great ape, the orangutan.
And those in Europe might have given rise to today’s African apes. A good candidate is Dryopithecus, first unearthed in France. Features of the ancient ape’s arms indicate it could probably swing through the trees like modern apes do. It also had a large frontal sinus, an air pocket in the forehead that produces mucus (also the site of dreadful sinus infections). This trait ties Dryopithecus to African apes. Gorillas, chimpanzees and humans all have a frontal sinus; orangutans, found only in Asia, do not.
Other European apes from around this time also shared characteristics with today’s African apes. For instance, Rudapithecus, an ape that lived in Hungary about 10 million years ago, also had a frontal sinus as well as a bevy of other characteristics seen in African apes, such as brow ridges and a downwardly bent face.
Begun and his colleagues think an ape like Dryopithecus or Rudapithecus returned to Africa and established the lineage of modern African apes. They point out the timing makes sense. The features that characterize gorillas and chimpanzees today evolved first in Europe, two million years before they appear in the African fossil record.
Apes may have left Europe in the later Miocene as climate change made Europe uninhabitable. The rise of the Himalayas made the continent much cooler and drier. Starting 9.5 million years ago, deciduous woodland replaced subtropical forests, and many tropical animals died out.
Luckily for us, at least some escaped before it was too late.
May 30, 2012
Last month, I wrote about how chimpanzee sleeping habits help anthropologists study the sleeping behavior of early hominids. Chimps typically build nests in trees when it’s time to go to sleep. Having an arboreal bed is likely a way to stay safe from prowling nighttime predators. Chimpanzees living in the Nimba Mountains of Guinea often sleep on the ground, probably because no chimp-eating animals live there. Millions of years ago, early hominids may have acted similarly.
But the study I reported on in April couldn’t explain why chimps preferred to sleep on the ground when it was an option. Recent work provides some answers.
David Samson and Kevin Hunt of Indiana University studied chimpanzee nesting in Uganda. They thought that differences in microclimate between the canopy and the ground might explain where the animals prefer to sleep. The pair set up portable weather monitors in trees and on the ground near nests from August 2010 to January 2011.
The ground is a cooler, less windy place to sleep, Samson and Hunt reported in the American Journal of Primatology. Chimpanzees sleeping in terrestrial nests probably spend less time trying to keep their beds stable in the face of unexpected gusts and therefore probably sleep more soundly throughout the night. Furthermore, based on estimates of temperature, wind speed, humidity and chimpanzee body mass, the researchers say the animals sleeping on the ground stay in “energy balance” while those sleeping in trees experience more thermal stress. In other words, sleeping on the ground is a more comfortable option. Still, despite the benefits of ground-sleeping, most chimpanzees in the Uganda study area have to sleep in trees because of the area’s lions and leopards.
The Nimba Mountain chimpanzees don’t have to worry about predators, so comfortable conditions on the ground could explain why ground-nesting is so common there. That’s something that still need to be tested, however. What’s happening in Uganda may not apply to the Nimba Mountains because the two regions have different habitats and climates; the Nimba Mountains are wetter.
And at least during part of the year, that wetness seems to deter ground-sleeping, suggests a recent study in the International Journal of Primatology. Over the course of 28 months in 2003 to 2008, Kathelijne Koops of the University of Cambridge in England and colleagues discovered tree-sleeping was most common during the wet season in the Nimba Mountains. During this time, chimps preferred sleeping in higher altitudes (more than 3,000 feet) and higher up in trees (almost 38 feet high). Koops and colleagues thought this could be a way to avoid disease-carrying mosquitoes, but the bugs were equally common throughout the year. Instead, it turns out chimpanzees make arboreal nests during the wettest time of the year to avoid humidity, which is higher near the ground and in lower elevations.
These recent studies reveal chimpanzee nesting is more complicated than just being a predator-deterrence strategy. Anthropologists should keep that in mind when they study early hominid behavior, too.