Here’s a round-up of recent science headlines we didn’t want you to miss!

Ancient Rivers

Without a smart phone or GPS device, how did early humans find their way out of Africa? A study published last week in PLoS One determines that ancient rivers, now covered by the Sahara Desert, provided habitable routes to follow.

Simulating paleoclimates in the region, the researchers found evidence of three major river systems that likely existed in North Africa 130,000–100,000 years ago, but are now largely buried by dune systems in the desert. When flowing, these rivers likely provided fertile habitats for animals and vegetation, creating “green corridors” across the region.

“It’s exciting to think that 100,000 years ago there were three huge rivers forcing their way across 1000-km of the Sahara desert to the Mediterranean—and that our ancestors could have walked alongside them,” says lead author Tom Coulthard of the University of Hull, UK.

Cosmic Beginnings?

Did life on Earth hail from Mars, as one researcher proposed last month, or comet collisions? Apparently, in both cases, it all has to do with the chemistry. Carl Zimmer, one of our favorite science writers, has a recent New York Times article about the chemistry needed to produce DNA from RNA. And while it doesn’t look like early Earth had those compounds, Mars might have.

Then, earlier this week, a study published in Nature Geoscience finds that the collision of icy comets with planetary bodies could result in the formation of complex amino acids, the building blocks of proteins (and life).

The researchers suggest that this process provides another piece to the puzzle of how life was kick-started on Earth, after a period of time between 4.5 and 3.8 billion years ago when the planet was being bombarded by comets and meteorites.

The team made their discovery by recreating the impact of a comet by firing projectiles through a large high-speed gun. This gun, located at the University of Kent, uses compressed gas to propel projectiles at speeds of 7.15 kilometers per second into targets of ice mixtures, which have a similar composition to comets. The resulting impact created amino acids such as glycine and D- and L-alanine. Sounds like a fun method of discovery…

Speaking of fun collisions, if you want more of them, the Morrison Planetarium at the Academy is featuring Cosmic Collisions in its current show rotation. From the our website:

Creative and destructive, dynamic and dazzling, collisions are a key mechanism in the evolution of the Universe.

Missing Mars Methane

One chemical Mars seems to be missing? Methane. The gas was sought as a possible sign of microbial life currently living on the seemingly barren world. However, despite earlier reports that NASA’s Mars rover, Curiosity, discovered methane on the red planet, NASA reports today in Science that none has been found.

Curiosity’s earlier evidence of methane detection turned out to be within leftover air from Earth. And previous reports of localized methane concentrations up to 45 parts per billion on Mars were based on observations from Earth and from orbit around Mars.

“It would have been exciting to find methane, but we have high confidence in our measurements,” says the report’s lead author, Chris Webster. “We measured repeatedly from Martian spring to late summer, but with no detection of methane.”

But don’t give up on microbial Martians just yet… “This important result will help direct our efforts to examine the possibility of life on Mars,” says NASA’s Michael Meyer. “It reduces the probability of current methane-producing Martian microbes, but this addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don’t generate methane.”

Looking for extraterrestrial life? Next month’s Brilliant!Science festival can deliver it to you. Visit this page for more information.

Image: the Tunable Laser Spectrometer on-board Curiosity: NASA/JPL-Caltech

Humans may have started cooking their food in pots 20,000 years ago or so, but when did it start to taste good?

According to a new study in PLoS ONE, maybe only 6,000 years ago. The study’s authors determined that’s around the time fledgling human chefs in Europe began using spices.

Previous studies, using classical texts and macrofossil evidence, had put the use of spices—plants that have little nutritional value but pack a flavorful wallop—back 4,000 years, but researchers from the University of York found a secret ingredient in phytoliths.

Phytoliths are the silica-rich structures formed when microscopic plants decay, as minerals take the place of the plant’s original tissue. The researchers found phytoliths in blackened deposits inside pottery shards recovered from sites in Denmark and Germany, dating from a period when prehistoric people transitioned from a hunter-gatherer lifestyle to farming.

The recovered phytoliths resemble those found in modern-day seeds of garlic mustard, a peppery mustard-flavored spice of little nutritional value. The shards also contained residues of fats from a range of marine and terrestrial animals, as well as starchy plants, suggesting the spice was used to flavor these foods.

Spicing up food must have caught on—several millennia later, Columbus and Vasco de Gama sailed the world in search of more spices.

“Until now it has been widely accepted that the calorific content of foods was of primary importance in the decisions by hunter-gatherers about what to eat,” says lead author Hayley Saul. “Both the actual finding of seed phytoliths consistent with garlic mustard spice, and the method of discovery, open up a new avenue for the investigation of prehistoric cuisines.”

As Emeril Lagasse might say, “Bam!”

Image: H. Saul

Maybe we ought to rethink those cavemen jokes. Researchers from the Max Planck Institute for Evolutionary Anthropology have discovered specialized bone tools made by Neanderthals more than 40,000 years ago.

The discovery leads scientists to challenge the notion that Neanderthals gained their tool-making skills from Homo sapiens—modern humans.

Neanderthals lived from about 200,000 to 28,000 years ago. Modern humans migrated to Europe about 40,000 years ago. Although evidence reveals that Neanderthals had cultural expression similar to modern humans, many anthropologists argue that these similarities only appear once modern humans came into contact with the original European group.

But the recent finds, leather-working tools called lissoirs, pre-date the arrival of modern humans. Lissoirs have been discovered at later Neanderthal and modern human sites and researchers believe the tools were used to fashion animal hides—making them softer and more waterproof. Modern artisans use similar tools today.

The earlier lissoirs were discovered at two sites in southwestern France. Using both radiocarbon dating and optically stimulated luminescence (OSL) dating to sediments at the site, the scientists estimate the date of the tools to close to 50,000 years ago, well before the arrival of modern humans.

“For now the bone tools from these two sites are one of the better pieces of evidence we have for Neanderthals developing on their own a technology previously associated only with modern humans,” explains Shannon McPherron, who discovered the lissoirs at one of the French excavation sites.

“If Neanderthals developed this type of bone tool on their own, it is possible that modern humans then acquired this technology from Neanderthals. Modern humans seem to have entered Europe with pointed bone-tools only, and soon after started to make lissoir[s]. This is the first possible evidence for transmission from Neanderthals to our direct ancestors,” says Marie Soressi, whose team found the bone tools at the other site.

Which species developed the tool first? We’ll let the anthropologists argue about that one…

The new findings are published this week in the Proceedings of the National Academy of Sciences.

Image courtesy of Abri Peyrony & Pech-de-l’Azé I Projects

Memories are unreliable, at least for humans.

According to MIT scientist (and Nobel Prize winner) Susumu Tonegawa, as quoted in Scientific American, only humans have false memories.

“Humans are the most amazing, imaginative animals,” he said. “We are thinking. Lots of things are going on. Humans are recording what happens and passing it on.”

An imperfect memory, Tonegawa said, may be the price we pay for the imagination and creativity that makes us human.

The phenomenon of humans’ false memory is well-documented—in many court cases, defendants have been found guilty on testimony from witnesses and victims who were sure of their recollections, but DNA evidence later overturned the conviction.

But now, Tonegawa and his colleagues have succeeded in also creating false memories in mice, hoping to further understand where and how these fake memories are made in the human brain.

Memories are stored in networks of neurons that form memory traces for each experience we have. Scientists call these traces engrams, and can identify the cells that make up part of an engram for a specific memory and reactivate it with a technology called optogenetics.

Using optogenetics, Tonegawa’s research team started the experiment by putting mice in a chamber and recording their memories of that chamber. The chamber was harmless and pleasant enough that the mice felt comfortable exploring the space. The next day, the researchers moved the mice into a different chamber, stimulating the memory of the previous chamber. The scientists also lightly shocked the rodents’ feet.

On the third day, the mice were placed back into the first chamber. They now froze in fear, even though they had never been shocked there. A false memory had been incepted—the mice feared the memory of the first chamber because when the shock was given in the second, they were reliving the memory of being in the first.

The team discovered they could both implant false memories and that the neurological traces of these false memories are identical in nature to those of authentic memories. “Whether it’s a false or genuine memory, the brain’s neural mechanism underlying the recall of the memory is the same,” says Tonegawa.

The MIT team is now planning further studies of how memories can be distorted in the brain.

The study is published in the current edition of Science.

Image: Steve Ramirez and Xu Liu

The old saying “You are what you eat” takes on new significance in the most comprehensive analysis to date of early human teeth from Africa.

Prior to about 3.5 million years ago, early humans dined almost exclusively on leaves and fruits from trees, shrubs, and herbs—similar to modern-day gorillas and chimpanzees.   However, about 3.5 million years ago, early human species like Australopithecus afarensis and Kenyanthropus platyops began to also nosh on grasses, sedges, and succulents—or on animals that ate those plants.

Evidence of this significant dietary expansion is written in the chemical make-up of our ancestors’ teeth.  These findings are reported in a series of four papers published this week in the Proceedings of the National Academy of Sciences, by an international group of scientists spread over three continents.

“These papers present the most exhaustive isotope-based studies on early human diets to date,” says the Academy’s own Zeresenay Alemseged, Senior Curator and Chair of Anthropology, and co-author on two of the papers (available here and here). “Because feeding is the most important factor determining an organism’s physiology, behavior, and its interaction with the environment, these findings will give us new insight into the evolutionary mechanisms that shaped our evolution.”

Plants can be divided into three categories based on their method of photosynthesis: C3, C4, and CAM.  C3 plants (trees, shrubs, and herbs) can be chemically distinguished from C4/CAM plants (grasses, sedges, and succulents) because the latter incorporate higher amounts of the heavier isotope carbon-13 into their tissues.  When the plants are consumed, the isotopes become incorporated into the animal’s own tissues—including the enamel of developing teeth.  Even after millions of years, scientists can measure the relative amounts of carbon-13 in teeth enamel and infer the amount of C3 vs. C4/CAM plants in an animal’s diet.

“What we have is chemical information on what our ancestors ate, which in simpler terms is like a piece of food item stuck between their teeth and preserved for millions of years,” says Alemseged.

These papers represent the first time that scientists have analyzed carbon isotope data from all early human species for which significant samples exist: 175 specimens representing 11 species, ranging from 4.4 to 1.3 million years in age.  The results show that prior to 3.5 million years ago, early humans ate almost exclusively C3 plants.  But starting about 3.5 million years ago, early humans acquired the taste for C4/CAM plants as well, even though their environments seemed to be broadly similar to their ancestors’.  The later genus Homo, including modern-day Homo sapiens, continues the trend of eating a mixture of C3 and C4/CAM plants—in fact, people who enjoy mashed potatoes with corn are practicing a 3.5 million-year-old habit.

What the studies cannot reveal is the exact identity of the food, and whether it also included animals that ate C4/CAM plants (an equally valid way to acquire carbon-13).  Possible C4/CAM-derived meals include grass seeds and roots, sedge underground stems, termites, succulents, or even small game and scavenged carcasses.  In 2010, Alemseged and his research team published the earliest evidence for meat consumption using tools, dating back to 3.4 million years ago—an additional line of evidence showing a dietary shift in human evolution.

“The change in isotopic signal documented by the new studies, coupled with the evidence for meat-eating in Australopithecus afarensis from Dikika around 3.5 million years ago, suggests an expansion in the dietary adaptation of the species,” says Alemseged.

The authors of this week’s papers also sampled fossils of giraffes, horses, and monkeys from the same environments and saw no significant change in their carbon isotope values over time—suggesting that the unique dietary transformation of early humans did not apply to other mammals on the African savanna.  The question of what drove the transformation, however, remains unresolved.

Andrew Ng is Communications Manager at the California Academy of Sciences.

Images: National Museums of Kenya. Photos by Mike Hettwer, Yang Deming

With six research papers in the current issue of Science, and numerous articles and blog posts surrounding those papers, Australopithecus sediba is the hominin du jour.

The papers reveal different anatomical features of Au. sediba and discuss their similarities to, and differences from, early human features. One news article calls them a “hodgepodge,” while another describes them as a “mosaic.”

“Amalgam” is how Zeray Alemseged, the Academy’s curator of anthropology, describes Au. sediba’s combination of human-like and more primitive features. Take the species’ heel. You and I walk by putting our broad and robust heel down and rolling to our toes, but Au. sediba’s heel was so narrow, these hominins couldn’t land on their heel, and likely walked on the sides of their feet and then pronated.

Similarly, Au. sediba’s torso had a conical and quite primitive shape, and their shoulders were “shrugged.” Alemseged explains, “With short necks and a narrow clavicle, they appeared to be ape-like with a substantial adaptation for climbing.”

However, the lower ribs were slightly human-like and the teeth were a mixture “of primitive and human traits,” according to an accompanying article in Science.

The findings are based on fossils found in South Africa by Lee Berger’s team in 2008, and include three skeletons.  The recent studies pinpoint Au. sediba’s existence to around 1.98 million years ago and make a few proposals on how to place the species in our lineage. In fact, Berger suggests that Au. sediba could be the direct ancestor to our genus, Homo.

“Lee is a good colleague, but I happen to disagree with him about that,” Alemseged says. “It’s a fascinating discovery and the quality of preservation of the fossils and number of skeletons are great,” but Alemseged sees no evidence that Homo descended from Au. sediba. “The fossil record indicates that by 2.33 million years ago, Homo already exists,” predating Au. sediba, Alemseged explains.

In addition, the findings (especially in regards to the dental study) suggest that Au. sediba was closely related to Australopithecus africanus, but not Australopithecus afarensis, the species Alemseged studies. He finds the evidence linking Au. sediba and Au. africanus solid, but that doesn’t leave Au. afarensis out. Given the timing, Au. afarensis, which lived between 3.8 and 2.9 million years ago, was likely the ancestor of Au. africanus, which lived between 3.3 and 2.1 million years ago and in turn was the ancestor of Au. sediba.

Alemseged notes that the studies underscore the diversity of our lineage. “It’s not surprising, in the natural world, to find multiple species of any given group,” so why should our family tree be any different?

Despite his scientific disagreement with his colleague, Alemseged lauds Berger’s generous sharing of the fossils and studies related to Au. sediba. “He’s introduced a new culture in paleontology of being very open.”

Finally, the image accompanying many of the articles (above right) is very similar to an animation comparing Au. afarensis, humans and chimpanzees in the Academy’s current exhibit, Human Odyssey that Alemseged curated. If you haven’t visited it yet, it explores Australopithecus, Homo, and more!

Image: Lee R. Berger And The University of the Witwatersrand

And that’s not all, according to a more recent study (last week, actually), sweet potatoes may tell us about early human exploration.

The sweet potato originates in South America, but the plant predates European explorers in Oceania. To many historians, this has always been a mystery. When did it get there? How? Natural seed dispersal? Humans?

A study in the 1970s by a Hawaiian researcher hypothesized that the sweet potato was first dispersed by Polynesian voyagers between 1000 and 1100, then by Spanish explorers heading from Mexico to the Philippines in 1500, and finally, by Portuguese traders traveling from Central America to Indonesia around the same time.

Called the tripartite hypothesis, the theory relied on archeological and linguistic evidence (the sweet potato is called kuumala in Polynesian languages, and kumara, cumar or cumal in Quechua speakers in South America). Now, French scientists are throwing genetic evidence into the mix.

The researchers analyzed 1,245 sweet potato samples from Central and South America as well as Oceania and a few from Southeast Asia and Madagascar. While most were modern plants, around 50 were historical herbarium specimens. And while the modern samples provide little evidence of early plant movement, the historical samples provide strong genetic support of the hypothesis, especially the first movement by Polynesian voyagers.

This stunning result implies that these voyagers may have traveled 5,000 miles or more across the open ocean!

The research was published last week in the Proceedings of the National Academy of Sciences. More information on the Polynesian travelers can be found here.

Image: Llez/Wikipedia