December 17, 2012
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.
December 12, 2012
South Africa plays a central role in the history of paleoanthropology. Anthropologists and other scientists of the 19th and early 20th century balked at the possibility that Africa was humankind’s homeland—until an ancient hominid was unearthed in South Africa in 1924. Since then, Africa has become the center of human evolution fieldwork, and South Africa has produced a number of iconic hominid fossils and artifacts. Here is a totally subjective list of the country’s most important hominid discoveries.
Taung Child: In 1924, anatomist Raymond Dart pried a tiny fossilized partial skull and brain from a lump of rock. The bones were the remains of a child. The youngster looked like an ape, but Dart also recognized some human qualities. He decided he had found a human ancestor that was so ancient it was still ape-like in many ways. (Later, scientists would determine the bones were nearly three million years old). Dart named the hominid Australopithecus africanus. The Taung Child, known by the name of the place where the fossils came from, was the first australopithecine ever discovered—and the first early hominid found in Africa. After the discovery, anthropologists who were searching for humanity’s origins in Europe and Asia switched their attention to Africa.
Mrs. Ples: Throughout the 1930s and 1940s, paleontologist Robert Broom led the efforts to find hominids in South Africa. He scoured the region’s limestone caves and quarries—the Taung Child came from a quarry—and was well rewarded for his efforts. Of the numerous fossils he uncovered (sometimes with the help of dynamite), his most influential find was a roughly 2.5-million-year-old skull of an adult female hominid now known as Mrs. Ples. Unearthed in 1947 at a site called Sterkfontein, the skull was well preserved and displayed the same mix of ape and human features seen in the Taung Child. Finding an adult version of A. africanus helped convince skeptics that the species was an ancient human ancestor. Some anatomists had thought Taung was just an ape and would have developed more pronounced ape-like features, and lost its human-like traits, as it grew up. Instead, Mrs. Ples showed that the species retained its mix of human and ape traits throughout life.
STS 14: Another one of Broom’s key finds is a set of well-preserved post-cranial bones that includes a pelvis, partial spine, ribs and upper thigh. Like Mrs. Ples, these fossils were found in 1947 at Sterkfontein and date to about 2.5 million years ago. The bones are officially known as STS 14 (STS refers to Sterkfontein) and presumably belonged to an A. africanus individual. The shape of the pelvis and spine are remarkably modern, and the find was some of the first evidence that early human ancestors walked upright on two legs.
SK 48: In addition to finding a trove of A. africanus specimens, Broom, along with his many assistants, discovered a new hominid species: Paranthropus robustus. The first hints of the species came in 1938 when Broom acquired a jaw fragment and molar that were much larger and thicker than any fossils belonging to A. africanus. Broom collected more of the unusual fossils and then hit the jackpot in 1950. A quarry worker found a nearly complete skull of an adult hominid that had giant teeth and a flat face. The fossil is officially called SK 48 (SK refers to the cave of Swartkrans where the skull was found). The collection of fossils with big chompers, which the hominids used to chew tough foods, was given the name P. robustus, which lived in South Africa about 1.8 million to 1.2 million years ago.
Little Foot: In the early 1990s, anthropologist Ron Clarke of South Africa’s University of the Witwatersrand found four small australopithecine foot bones at Sterkfontein. Later, Clarke and his colleagues discovered a nearly complete skeleton embedded in limestone that belonged to the foot. The researchers are still carefully chipping away at the rock to release the skeleton, dubbed Little Foot, but they have already noted that the individual has some characteristics not seen in any other known species of Australopithecus. But since the bones haven’t been fully studied and shared with other scientists, it’s hard to know where the hominid sits in the family tree, Science reported last year. It’s also hard to know exactly how old it is. Clarke’s team places the fossils at 3.3 million years old while other groups using different dating methods say Little Foot is more like 2.2 million years old. Science reported that Little Foot was expected to be fully liberated from its rocky enclosure sometime this year. As far as I know, that hasn’t happened yet.
Australopithecus sediba: The most recent major hominid fossil discovery in South Africa occurred in 2010. Lee Berger of the University of the Witwatersrand led a team that found two partial hominid skeletons at Malapa Cave. Dating to nearly two million years ago, the skeletons indicate that these hominids had their own unique style of walking and spent time both on the ground and in trees. X-ray scans of one of the skulls reveals that some aspects of the brain were more modern than in previous species. Berger and his colleagues therefore think the species, which they named A. sediba, could have given rise to the genus Homo.
Origins of Modern Behavior: Fossils aren’t the only major human evolution discoveries from South Africa. Several coastal cave sites have been treasure troves of artifacts that reveal when and how sophisticated behavior and culture emerged in early populations of Homo sapiens. There have been too many of these discoveries to single any one out. Some of these finds—such as red pigments used 164,000 years ago and shell beads dating to 77,000 years ago—are among the earliest evidence for symbolic thinking in our ancestors. Other artifacts, like 71,000-year-old projectile weapons, indicate early humans could construct complicated, multipart tools that require a lot of planning and foresight to make.
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.
December 5, 2012
Perhaps no other human trait is as variable as human height. At 5’4″, I’d be dwarfed standing next to 6’3″ Kerri Walsh, the 2012 Olympic gold medalist in beach volleyball. But next to an African pygmy woman, I’d be a giant. The source of that variation is something that anthropologists have been trying to root out for decades. Diet, climate and environment are frequently linked to height differences across human populations.
More recently, researchers have implicated another factor: mortality rate. In a new study in the journal Current Anthropology, Andrea Bamberg Migliano and Myrtille Guillon, both of the University College London, make the case that people living in populations with low life expectancies don’t grow as tall as people living in groups with longer life spans. They also argue changes in mortality rates might account for the jump in body size from Australopithecus to Homo some 2 million years ago.
From an evolutionary standpoint, Migliano and Guillon note, it’s beneficial to start reproducing as soon as possible if you live in a society where individuals typically die young. That way you can have as many babies as possible in a short amount of time. Thus, you should stop growing relatively early in life and start devoting your energy to having children and taking care of them. Having a shorter developmental period means you can’t grow as tall, on average, as someone who has more time to mature. But getting big has reproductive benefits: Larger individuals tend to take in more energy and therefore can invest more energy in reproducing. So in societies with lower mortality rates, and longer adulthoods, it’s better to mature slowly and grow bigger and taller. Over time, populations experiencing different mortality rates will adapt to have shorter or longer developmental periods—and therefore be shorter or taller. (Of course, there is also variation within a population. But here, and throughout the post, I’m talking about population averages.)
To investigate this idea, Migliano and Guillon looked at previously collected height and mortality data from 89 small-scale populations from all over the world. These groups live in a variety of environments, including deserts, forests and savannas, and have different subsistence strategies, including hunter-gathering, pastoralism and agriculture. Using statistical analyses, the team wanted to see what kind of factors best explained the variation of heights in their data set.
In one analysis, three measures of survivorship—life expectancy at birth, life expectancy at age 15 and probability of survival to age 15—accounted for about 70 percent of height variance. The researchers also found evidence that people from societies with high mortality rates do indeed develop faster: Girls from groups that have low life expectancies start menstruating earlier than girls who are more likely to live longer. Environmental setting also influenced height, with people from savannas tending to be taller than people from forests. Diet, however, seemed to play a much smaller role, at least in the study samples.
Other variables not considered in the study may also contribute to height variation, the researchers point out. Temperature and humidity probably somehow factor in. For example, some work suggests shorter people generate less heat in hot, humid environments and therefore cool down more efficiently. That might explain why people living in tropical forests are shorter than those from savannas.
There are some situations, however, where the study’s findings don’t hold up. In modern Western societies, where mortality rates are low, growth is actually sped up because of an overabundance of food. Some studies now show that obesity may contribute to early puberty in girls. On the other hand, severe malnourishment can lead to delayed growth.
Based on the study’s findings, Migliano and Guillon suggest lower death rates probably contributed to changes in body size and height during the Australopithecus-Homo transition. In one study, anthropologists estimated early Homo species were about 30 percent bigger than australopithecines. Homo erectus grew even taller, within the range of variation of modern people. The larger brain of the genus Homo may have allowed the group to lower its mortality rate by outsmarting predators or foraging more efficiently than Australopithecus. Within H. erectus, differences in mortality rates between populations—which lived over a much larger geographic expanse than australopithecines—probably accounts for the variation of height seen in the fossil record of that species.
Much more investigation is needed to corroborate the link between death and height in the fossil record. But the work does highlight how even seemingly simple physical features have complex evolutionary histories.
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?