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Fossils discovered in Kenya indicate multiple species of Homo lived roughly two million years ago. One of the new jaws is pictured here with a previously found Homo rudolfensis skull. Image: © Photo by Fred Spoor

As 2012 nears its end, one thing stands out as the major theme in human evolution research this year: Our hominid ancestors were more diverse than scientists had ever imagined. Over the past 12 months, researchers have found clues indicating that throughout most of hominids’ seven-million-year history, numerous species with a range of adaptations lived at any given time. Here are my top picks for the most important discoveries this year.

1. Fossil foot reveals Lucy wasn’t alone: Lucy’s species, Australopithecus afarensis, lived roughly 3.0 million to 3.9 million years ago. So when researchers unearthed eight 3.4-million-year-old hominid foot bones in Ethiopia, they expected the fossils to belong to Lucy’s kind. The bones do indicate the creature walked upright on two legs, but the foot had an opposable big toe useful for grasping and climbing. That’s not something you see in A. afarensis feet. The researchers who analyzed the foot say it does resemble that of the 4.4-million-year-old Ardipithecus ramidus, suggesting that some type of Ardipithecus species may have been Lucy’s neighbor. But based on such few bones, it’s too soon to know what to call this species.

2. Multiple species of early Homo lived in Africa: Since the 1970s, anthropologists have debated how many species of Homo lived about two million years ago after the genus appeared in Africa. Some researchers think there were two species: Homo habilis and  Homo rudolfensis; others say there was just H. habilis, a species with a lot of physical variation. It’s been a hard question to address because there’s only one well-preserved fossil, a partial skull, of the proposed species H. rudolfensis. In August, researchers working in Kenya announced they had found a lower jaw that fits with the previously found partial skull of H. rudolfensis. The new jaw doesn’t match the jaws of H. habilis, so the team concluded there must have been at least two species of Homo present.

3. New 11,500-year-old species of Homo from China: In March, researchers reported they had found a collection of hominid bones, dating to 11,500 to 14,300 years ago, in a cave in southern China. Based on the age, you’d expect the fossils to belong to Homo sapiens, but the bones have a mix of traits not seen in modern humans or populations of H. sapiens living at that time, such as a broad face and protruding jaw. That means the fossils may represent a newly discovered species of Homo that lived side by side with humans. Another possibility is that the remains came from Denisovans, a mysterious species known only from DNA extracted from the tip of a finger and a tooth. Alternatively, the collection may just reveal that H. sapiens in Asia near the end of the Pleistocene were more varied than scientists had realized.

4. Shoulder indicates A. afarensis climbed trees: Another heavily debated question in human evolution is whether early hominids still climbed trees even though they were built for upright walking on the ground. Fossilized shoulder blades of a 3.3-million-year-old A. afarensis child suggest the answer is yes. Scientists compared the shoulders to those of adult A. afarensis specimens, as well as those of modern humans and apes. The team determined that the A. afarensis shoulder underwent developmental changes during childhood that resemble those of chimps, whose shoulder growth is affected by the act of climbing. The similar growth patterns hint that A. afarensis, at least the youngsters, spent part of their time in trees.

5. Earliest projectile weapons unearthed: Archaeologists made two big discoveries this year related to projectile technology. At the Kathu Pan 1 site in South Africa, archaeologists recovered 500,000-year-old stone points that hominids used to make the earliest known spears. Some 300,000 years later, humans had started making spear-throwers and maybe even bow and arrows. At the South African site called Pinnacle Point,  another group of researchers uncovered tiny stone tips dated to 71,000 years ago that were likely used to make such projectile weapons. The geological record indicates early humans made these small tips over thousands of years, suggesting people at this point had the cognitive and linguistic abilities to pass on instructions to make complex tools over hundreds of generations.

6. Oldest evidence of modern culture: The timing and pattern of the emergence of modern human culture is yet another hotly contested area of paleoanthropology. Some researchers think the development of modern behavior was a long, gradual buildup while others see it as progressing in fits and starts. In August, archaeologists contributed new evidence to the debate. At South Africa’s Border Cave, a team unearthed a collection of 44,000-year-old artifacts, including bone awls, beads, digging sticks and hafting resin, that resemble tools used by modern San culture today. The archaeologists say this is the oldest instance of modern culture, that is, the oldest set of tools that match those used by living people.

7. Earliest example of hominid fire: Studying the origins of fire is difficult because it’s often hard to differentiate a natural fire that hominids might have taken advantage of versus a fire that our ancestors actually ignited. Claims for early controlled fires go back almost two million years. In April, researchers announced they had established the most “secure” evidence of hominids starting blazes: one-million-year-old charred bones and plant remains from a cave in South Africa. Because the fire occurred in a cave, hominids are the most likely cause of the inferno, the researchers say.

8. Human-Neanderthal matings dated: It’s not news that Neanderthals and H. sapiens mated with each other, as Neanderthal DNA makes up a small portion of the human genome. But this year scientists estimated when these trysts took place: 47,000 to 65,000 years ago. The timing makes sense; it coincides with the period when humans were thought to have left Africa and spread into Asia and Europe.

9. Australopithecus sediba dined on wood: Food particles stuck on the teeth of a fossil of A. sediba revealed the nearly two-million-year-old hominid ate wood—something not yet found in any other hominid species. A. sediba was found in South Africa in 2010 and is a candidate for ancestor of the genus Homo.

10. Earliest H. sapiens fossils from Southeast Asia: Scientists working in a cave in Laos dug up fossils dating to between 46,000 and 63,000 years ago. Several aspects of the bones, including a widening of the skull behind the eyes, indicate the bones were of H. sapiens. Although other potential modern human fossils in Southeast Asia are older than this find, the researchers claim the remains from Laos are the most conclusive evidence of early humans in the region.

An artist’s reconstruction of Purgatorius, a probable primate ancestor. Image: Nobu Tamura/Wikicommons

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.

This X-ray of a human skull highlights the main nasal cavity (orange) and the sinuses: frontal (pink), ethmoid (yellow), maxillary (green) and sphenoid (purple). Asian apes do not have frontal or ethmoid sinuses. Image: Hellerhoff/Wikicommons

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.

Dating and mapping fossil finds is one way anthropologists track early human migrations. The bones from Qafzeh, Israel, (a drawing of one of the skulls, above) indicate Homo sapiens first left Africa more than 100,000 years ago. Image: José-Manuel Benito/Wikicommons

By 200,000 years ago, Homo sapiens had emerged somewhere in Africa. By 14,000 years ago, our species had spread to every continent except Antarctica. What happened in between—the pattern of where humans went and when—is still being worked out. To reconstruct the peopling of the world, anthropologists rely on several types of clues.

Fossils: The most obvious way to track our ancestors’ movements is to look for their physical remains. Researchers sketch out travel routes by mapping where the oldest human fossils are found. The earliest Homo sapiens bones outside of Africa come from a cave site in Israel called Qafzeh. Here the skeletons of both adults and children date to as far as 125,000 years ago. This first foray out of Africa didn’t last long. Humans disappeared from the fossil record outside of Africa for many tens of thousands of years, perhaps because the climate became too harsh. Fossils tell us humans made a successful, sustained exodus by at least 50,000 years ago. Human fossils found at Australia’s Lake Mungo site, for example, have been dated to between 46,000 and 50,000 years ago (PDF).

The problem with relying on skeletal remains to map early migrations is that the timing of our ancestors’ travels is only as good as the methods used to date the fossils. Sometimes scientists find bones in places that are not easily dated by geological techniques. And in some areas, fossils aren’t prone to preservation, so there are probably huge gaps in our knowledge of the paths early humans took as they spread around the world.

Artifacts: Archaeologists also look for the items people made and left behind. For example, stone tool discoveries suggest an alternative route out of Africa. For decades, scientists assumed humans left Africa via the Sinai Peninsula, but in the last several years some researchers have favored a “southern” route: leaving from the Horn of Africa, crossing the narrowest part of the Red Sea and entering into southern Arabia. Last year, archaeologists reported finding stone tools in Oman dating to roughly 106,000 years ago. At that time, the Arabian Peninsula was a much more hospitable place than it is today, home to numerous freshwater lakes. As the region became drier, people might have moved east into Asia or returned to Africa.

Of course, when the only remains at an archaeological site are tools, it’s hard to say with absolute certainty who made them. The researchers working in Oman noted that the tools they found in Arabia match the technology of modern humans found in eastern Africa about 128,000 years ago. The team made the case that the tool makers on either side of the Red Sea belonged to the same cultural group—and therefore the same species. But as anthropologists discover more species, such as the Hobbit or the Denisovans, that lived alongside modern humans outside of Africa up until a few tens of thousands of years ago, it becomes harder to say stone tools alone indicate the presence of Homo sapiens.

DNA: Genetic data can help fill in the holes in the human migration story that fossils and artifacts can’t address. Anthropologists collect DNA samples from different ethnic groups around the world. Next, they count up the genetic differences caused by mutations in certain sections of the genome. Groups that are more closely related will have fewer genetic differences, which implies they split off more recently form each other than they did with more distantly related groups. Scientists calculate when in the past different groups diverged from each other by adding up all of the genetic differences between two groups and then estimating how often genetic mutations occurred. Such analyses not only give a sense of when different parts of the world were first inhabited, but they can also reveal more intricate patterns of movement. For example, genetic data suggest North America was colonized by three separate waves of people leaving Siberia across the Bering Strait.

Genetic data are not foolproof, however. The estimated divergence times are only as accurate as the estimated mutation rate, which scientists still debate. In the early days of DNA studies, scientists used either mitochondrial DNA, passed down only by the mother, or the Y chromosome, inherited only from father to son. Neither of these types of DNA presented the full picture of what people were doing in the past, as mitochondrial DNA only tracks maternal lineages while the Y chromosome only follows paternal lines. Today, whole genome sequencing is beginning to allow researchers to trace entire populations.

Languages: Anthropologists use languages in methods analogous to studying DNA; they look for patterns of similarities, or differences, in vocabularies or other aspects of language. Earlier this year, researchers compared different languages within the Indo-European language family to determine where these languages arose. After assessing the relationship between the languages, the researchers considered the geographic ranges where those languages are currently spoken. They concluded that the Indo-European language family originated in what is today Turkey and then spread west into Europe and east into southern Asia as people moved into these areas. But such linguistic analyses may only track relatively recent migration patterns. For example, H. Craig Melchert, a linguist at the University of California, Los Angeles, told Science News that the Indo-European languages can only be traced back about 7,000 years.

Neanderthals may have collected feathers from dark birds, such as black vultures (shown), for ornamental purposes, a new study suggests. Image: kenschneiderusa/Flickr

Neanderthals have a reputation for being dumb brutes. While modern humans (Homo sapiens) were painting cave murals, sculpting tiny figurines and crafting beaded jewelry some 30,000 to 50,000 years ago, Neanderthals weren’t making any art. At least, that’s the way it appears in the archaeological record. Now, a new study of bird fossils suggests our cousins were indeed capable of expressing themselves symbolically—using feathers as personal adornments.

In the last few years, researchers have reported a few archaeological sites with evidence that Neanderthals removed feathers and claws from birds such as raptors, presumably for ornamental purposes. Clive Finlayson of the Gibraltar Museum and his colleagues wanted to see how widespread this behavior was among Neanderthals. They published their findings last week in PLOS One.

To address the question, the team looked at Neanderthals’ association with fossils of raptors (including vultures and eagles) and corvids (including ravens and magpies). They focused on these birds because modern people generally don’t consume them and therefore Neanderthals probably didn’t either. Thus, finding these types of birds at an archaeological site helps exclude the possibility that our cousins were eating them. In searching almost 1,700 sites across Europe and Asia that contain bird fossils, the team noted that species with dark plumage were more common at Neanderthal sites than would be expected by chance alone. So, it seems Neanderthals across their geographic range liked black birds.

Next, the researchers looked at three cave sites on Gibraltar to examine more closely what Neanderthals might have been doing with these birds. The caves date from 57,000 to 28,000 years ago, before modern humans entered the region. The team found 604 avian skeletal pieces, representing at least 124 individual birds. With less than 3 percent of the bones containing the tooth marks of rodents or carnivores, Neanderthals are the likely reason the birds were brought into the caves.

More than half of the bones were wing bones. There’s no reason to expect wing bones to be disproportionately preserved in the fossil record, so this is another sign that Neanderthals were mainly interested in feathers, the researchers say. Furthermore, most of the bones with stone-tool markings are the wing bones. If Neanderthals were butchering the animals for meat, you’d expect to find the most markings on bones connected to fleshy areas, such as the breast bone.

Because soil bacteria rapidly decompose feathers, the researchers conclude our cousins weren’t using feathers as bedding. The only use that makes sense, Finlayson and colleagues argue, is plucking feathers to make headdresses, cloaks or some other adornment.

“Neanderthals, though different in a number of ways from modern humans, had comparable cognitive capacities that included symbolic expression,” the researchers write. Furthermore, they say, any differences in the art or artifacts left behind by the two species was the result of cultural differences, not intellect.

But does the capacity for symbolic expression mean Neanderthals had mental abilities that were on par with modern humans? It depends on who you ask. For decades, symbolism was considered the key cognitive trait that separated modern humans from other hominids. Today, anthropologists think there may be a range of abilities that define the human mind, such as planning for the future and processing disparate chunks of information at the same time (working memory). Until researchers can agree on the core features that characterize human cognition, it will be impossible to determine whether Neanderthal brains were really just like ours.