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 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?
July 17, 2012
A hundred years ago, archaeologists thought Native Americans came to North America only 5,000 years ago. That belief changed in the 1920s and 1930s as researchers started finding stone projectile points associated with the fossils of mammoths and giant bisons—animals that went extinct more than 10,000 years ago. For decades, the oldest known points dated to 13,000 years ago. Called Clovis points, they contained characteristic “flutes,” or long, concave grooves, where a spear locked into place.
More recent evidence reveals humans reached the New World, via the Bering Strait, by at least 15,000 years ago. These early Americans weren’t making Clovis points. Last week, archaeologists announced in Science another example of pre-Clovis technology.
The tools come from Oregon’s Paisley Caves. Dennis Jenkins of the University of Oregon and colleagues determined people were living in the area by at least 14,000 years ago based on the radiocarbon dates of human coprolites (fossilized dung) found in the cave. They also found projectile points of the same age or slightly older than Clovis points. Known as the Western Stemmed Tradition, these points are narrower, lack flutes and require a different chipping method to make than Clovis points.
The team suggests the Clovis and Western Stemmed points probably developed independently from an even earlier tool technology, with the Clovis originating in the Plains and Southeast and the Western Stemmed arising in the West. This fits with a discovery reported last year in Science. At the Debra L. Friedkin site in central Texas, archaeologists recovered more than 16,000 artifacts dating to 13,200 to 15,500 years ago. Among the artifacts were blades and two-sided flakes that Clovis tools could have evolved from, the researchers suggested. (A study published online in the Journal of Archaeological Science, however, challenges those dates and even argues that the artifacts may actually be Clovis tools.)
In other early American news, a team led by David Reich of Harvard Medical School reconstructed the ancestry of Native Americans living in North and South America. They reported their findings last week in Nature. Based on a genetic analysis of 52 modern Native American groups and 17 Siberian groups, the researchers concluded the majority of Native Americans descend from a single Siberian population. Arctic people who speak Eskimo-Aleut languages also inherited about half of their genetic material from a second wave of Siberian immigrants. Members of a third migration contributed to the gene pool of Na-Dene-speaking Chipewyans of Canada. Finding multiple migrations complements previous genetic, archaeological and linguistic studies.
Of course, that doesn’t mean there were only three migrations to the New World. The researchers only looked at the ancestry of living Native Americans. There could be early migrating groups that didn’t leave behind living descendants. That’s something we may never know.
June 18, 2012
Humans and Neanderthals are close cousins. So close, in fact, that some researchers argue the two hominids might actually be members of the same species. But a few years ago, anthropologists discovered a mysterious new type of hominid that shook up the family tree. Known only from a finger fragment, a molar tooth and the DNA derived from both, the Denisovans lived in Asia and were contemporaries of Neanderthals and modern humans. And they might have been Neanderthals’ closest relatives. A recent study of virus “fossils” provides new evidence of this relationship.
Hidden inside each, embedded in our DNA, are the genetic remnants of viral infections that afflicted our ancestors thousands, even millions of years ago. Most known virus fossils are retroviruses, the group that includes HIV. Consisting of a single strand of RNA, a retrovirus can’t reproduce on its own. After the retrovirus invades a host cell, an enzyme reads the RNA and builds a corresponding strand of DNA. The virus-derived DNA then implants itself into the host cell’s DNA. By modifying the host’s genetic blueprints, the virus tricks the host into making new copies of the retrovirus.
But sometimes the host fails to make new copies of the virus. If this happens in a sperm or egg cell, the virus DNA becomes a permanent part of the host’s genome and is passed on from generation to generation. These virus fossils have distinct genetic patterns that scientists can identify during DNA analyses. After the Human Genome Project was finished in 2003, researchers estimated that about 8 percent of human DNA is made up of virus DNA.
With that in mind, a team led by Jack Lenz of the Albert Einstein College of Medicine in New York used virus fossils as a way to sort out the degree of relatedness among humans, Neanderthals and Denisovans. The researchers discovered that most of the ancient viruses found in Denisovans and Neanderthals are also present in humans, implying that all three inherited the viral genetic material from a common ancestor. However, the team also found one virus fossil present in Neanderthals and Denisovans that is missing in humans. This implies Denisovans are more closely related to Neanderthals than we are, the researchers reported in Current Biology. Humans must have split off from the lineage leading to Neanderthals and Denisovans; then the infection occurred, and then Neanderthals and Denisovans split from each other.
This finding was not necessarily unexpected, as a previous genetic analysis also suggested Neanderthals and Denisovan are each other’s closest relatives. But it’s always nice to have confirmation. And the work demonstrates how ancient infections can be useful in the study of evolution.
April 23, 2012
Chimpanzees know how to make a bed. Every night they climb up trees and curl up in nests they build out of branches and leaves. They sleep in the treetops to avoid nighttime predators such as leopards. Many anthropologists think early hominids did the same thing when it was time to catch some zzz’s. But at least one population of chimpanzees enjoys sleeping on the forest floor, new research shows. This may mean that some early hominids did, too.
The ground-sleeping chimps live in the Nimba Mountains of southern Guinea. Kathelijne Koops of the University of Cambridge in England and colleagues analyzed 634 chimp nests there from 2006 to 2008. About 14 percent of these beds were on the ground. In most chimpanzee populations, less than 5 percent of nests are on the ground, the team reports in the American Journal of Physical Anthropology.
What’s different about these chimps? They do not lack appropriate trees, the team notes. But the area does seem to be missing the dangerous nocturnal predators that force other chimps to rest in trees. Without this pressure, Koops and her colleagues hypothesized, male chimps might be camping out beneath the trees of females they wanted to mate with, to keep other males away.
To test that idea, the researchers turned to DNA. They collected hair in 46 ground nests to analyze the owners’ genetic material to determine their sex. Thirty of the nest-makers were male, four were female, and the sex couldn’t be determined for 12, the researchers found. Since ground-nesting is largely a male behavior, it lends support to the idea that this could be a male mate-guarding strategy—but the males don’t appear to be slumbering beneath the beds of females. In analyses of tree nests above the ground nests, it turns out most males were resting below other male relatives. So the mate-guarding hypothesis doesn’t seem to hold up. For now, it’s unclear what motivates chimps in this community to sleep on the forest floor.
So what does this have to do with our ancestors? Anthropologists have looked to chimpanzee sleeping habits as a proxy for early hominids because early hominid beds aren’t preserved in the fossil record. (The earliest known hominid bed dates to 77,000 years ago.) Even though our earliest ancestors probably spent most of their time walking upright on the ground, their skeletal features reveal that they still retained some climbing capabilities. And since they were vulnerable to predators, anthropologists reason, they were probably safer in the trees, just as most chimps are today. Researchers speculate it wasn’t until Homo erectus, which had a modern body plan, that hominids started sleeping on the ground.
But the new research suggests that perhaps under certain circumstances, some earlier hominids snoozed on the ground as well. But more than that, I think the study reminds us that individuals within a species are variable, and not all populations behave the same. Chimpanzees in different parts of Africa, for example, eat different foods, use different tools and apparently build nests in different parts of the forest. It’s likely that in any given species of early hominid, individuals behaved differently both within and between different communities. Studying this variation in our early ancestors is an almost impossible task because most species have been found in only a handful of locations. And as with sleeping, some behavior doesn’t leave a mark on the fossil record. So analyzing the circumstances under which particular behaviors of modern animals vary—and looking for ways to correlate that to evidence that gets preserved in the fossil record—is a crucial aspect of human evolution studies.