Catching glimpses into our fossil ancestors’ daily lives is a tricky business. Fossil remains of our ancestors can only tell us so much concrete information, and tracing our DNA backwards in time can only get us so far.

But bones and teeth hold more clues than you’d think, if you just know how to extract them. In a new research paper published in the journal Nature, evolutionary anthropologists harnessed cutting-edge chemical tools and analyses to uncover the social patterns of our earliest ancestors and in so doing, discovered that males weren’t too keen on leaving their childhood homes.

The study, led by Sandi Copeland of the Max Planck Institute for Evolutionary Anthropology, looked at fossilized teeth from South Africa: eight Australopithecus africanus (2.2 million years ago) individuals and 11 individuals belonging to the Paranthropus robustus (1.8 million years ago) species. Using a laser, the team extracted a key element from the tooth enamel called strontium.

The strontium found in tooth enamel is like a snapshot into where the person lived during childhood, when permanent teeth developed. The various types of strontium, called isotopes, can be connected with specific geographical regions. “The strontium isotope ratios are a direct reflection of the foods these hominids ate, which in turn are a reflection of the local geology,” Copeland explains.

The research team divided sets of teeth for both species into male and female based on size (male teeth are generally larger). They then performed strontium isotope analysis on each, looking for clues into the each specimen’s childhood geographical landscape. They found that a large majority of male specimens – nearly 90% – grew up in the same general area where the fossilized teeth were uncovered. They were born, grew up, and died in pretty much the same place: the prehistoric equivalent of their hometown.

But analysis of female strontium isotopes revealed a different history. Over 50% of female remains trace to further afield, away from the dolomite cave systems that so many males grew up near. It seems that many females spent their formative years elsewhere, only arriving in the area once they reached adulthood.

Chimpanzees, our closest living primate relatives, exhibit a similar social structure. Male chimps are highly territorial, and will not leave their home base, even upon reaching adulthood. To prevent inbreeding, females are often forced to leave their childhood groups in search of new mating partners in other groups. Copeland’s strontium-isotope analysis lends support to the idea that early hominids might have done the same. If this structure exists in both chimpanzees and early hominids, perhaps its origins extend much further back in time.

“One of our goals was to try to find out something about early hominin landscape use. Here we have the first direct glimpse into the geographic movements of early hominids,” says Copeland.

The study not only provides insight into previously unknown aspects of ancient hominin social structure, it also highlights exactly how much new information can be squeezed out of a fossil specimen. As Julia Lee-Thorp, one of the study’s co-authors, explains, “Studies like these really bring home that finding and describing fossils is not the end of the story. Thoughtful application of these new analytical methods can tell us such a lot more about the details and lives of the distant past.”

Anne Holden, a docent at the California Academy of Sciences, is a PhD trained genetic anthropologist and science writer living in San Francisco.

Image: Darryl de Ruiter

Since scientists like Jane Goodall started studying chimpanzees over 40 years ago, we humans have begun to realize that our primate brethren aren’t so different from us after all. They have a complex social structure, care for their young, and some in captivity have even learned sign language. Now recent observations have revealed another aspect of chimpanzee ‘culture’ that had previously been thought to be unique to young human girls: playing with dolls.

Primatologists have long seen chimpanzees in the wild playing with inanimate objects. Small stones, clumps of dirt, and sticks as playthings are a common sight in well-known communities like the Kanyawara chimpanzee community in Kibale National Park, Uganda. But experts like Richard Wrangham of Harvard University and Sonya Kahlenberg of Bates College in Maine thought there was more to this type of play than meets the eye. They reported their findings in the December 21^st issue of Current Biology.

Wrangham and Kahlenberg focused on one particular behavior called “stick-carrying,” in which a chimp will carry a small stick or twig around with them for an extended period of time. The scientists noticed an uncanny similarity between the way that chimps were carrying these sticks and the way that young human girls carry dolls.

“We thought that if the sticks are being treated like dolls, females would carry sticks more than males do,” said Wrangham. When analyzing their years of data and observations, Wrangham and Kahlenberg found exactly that. Further, they found this behavior almost exclusive to young female chimps. Male chimps almost never played with sticks in this manner. According to Wrangham, “this is the first evidence of an animal species in the wild in which object play differs between males and females.”

Kahlenberg believes that these observations are akin to play mothering, similar to how girls play with dolls when they are young. “We have no records of adult females carrying sticks once they have given birth to their first offspring, which suggests a link with play mothering,” Kahlenberg told the Academy. Observations also suggested that young female chimps were learning this behavior not from their mothers but from each other.

The potential implications of these findings could revolutionize our understanding of chimpanzee behavior. According to Wrangham, this may very well be “the first case of a tradition maintained just among the young, like nursery rhymes among human children,” suggesting that chimpanzee traditions may be even more human than previously thought.

Anne Holden, a docent at the California Academy of Sciences, is a PhD trained genetic anthropologist and science writer living in San Francisco.

Photo: Sonya Kahlenberg

Human brains vs. Neanderthal brains

German and French researchers compared CT scans of human and Neanderthals at various growth stages and published their results in Current Biology. The brains in each species started out the same size and shape, but as each grew, their shapes changed. Both begin elongated, but human brains become more round and globular. Despite having similarly large brains, according to Science Now:

The differences suggest that Neandertals did not see the world the same way we do and may not have been as adept at language or forming complex social networks.

Human brains vs Chimpanzee brains

Excitingly, the same researchers had another similar study published last Friday. Using the same scanning techniques, they compared chimp and human brains at different ages. Unlike the Neanderthals, even at birth, the brain shape is different and in fact, according to the paper, “there is no overlap between the two species throughout ontogeny.” In addition, “the shape changes associated with this early “globularization phase” are unique to humans.”

Another study published last week in PLoS Genetics explains a by-product of this brain uniqueness—a weaker immune system. It all has to do with a type of white blood cells called natural killer cells, or NK cells. NK cells are crucial in fighting disease in both chimpanzees and humans, but they do a better job in chimps— chimps are not susceptible to diseases like HIV and malaria.

Human NK cells seem to have evolved differently. NPR had a great story on the research this week.

The kind of NK cells that are good for getting lots of blood to the developing fetus are not as good for dealing with infection, and vice versa.

And whereas the chimpanzees develop the cells good for infections,

The human system, on the other hand, seems to be optimized for getting lots of blood to the developing fetus so our big brains can grow the way they’re supposed to.

More Human Brain

Finally, how about two items that are good for the brain? A study published in PLoS One yesterday shows that the video game Tetris may reduce Post-Traumatic Stress flashbacks.  And Jonah Lehrer, one of our favorite neuroscience writers, has a great blog post in Wired today about the pleasure we get from preparing our own meals.

Image from Science- Credit: (baby skulls, L) P. Gunz et al., Current Biology, 20 (9 November 2010); (Adult skulls) Philipp Gunz/MPI EVA Leipzig