- Possible New Human Ancestor Discovered
- Mystery Object Defies Astronomical Classification
- Pigeon Flocks Let the Best Bird Lead
- First Animals Found That Live Without Oxygen
- New Giant Lizard Discovered in the Philippines
- Gut Bacteria Give Super Seaweed-Digestion Power to Japanese
Posted: 08 Apr 2010 07:53 AM PDT
Two 1.9 million-year-old skeletons found in a South African cave have added a new and intriguing member to the primate family.
Dubbed Australopithecus sediba, it has many features —including long legs and a protruding nose —common to Homo, the genus that eventually spawned humans. Other features, such as extra-long forearms and flexible feet, date from deep in our primate past.
Paleontologists disagree over whether A. sediba is a direct human ancestor, or just looks like one. But whatever their lineage, the fossils provide rare insight into a period shrouded in paleontological mystery.
"We feel that A. sediba might be a Rosetta Stone for defining for the first time what the genus Homo is," said paleontologist Lee Berger of the University of Witwatersrand. "They're going to be a remarkable window, a time machine."
The skeletons, described April 8 in Science, were found two years ago in a South African cave where they fell two million years ago.
On one side of that date in the fossil timeline are the various species of Australopithecus, the first great apes to walk on two feet. On the timeline's other side is the Homo genus, the first creatures whom one would recognize —with all due respect to Lucy's famous A. Afarensis — as close to human.
In between is uncertainty. The fossil record is mostly bare. Some Australopithecus lineage split, with one branch becoming Homo. But the identity of that lineage, and the characteristics of early Homo, are unknown.
According to Berger's team, A. sediba's combination of old and new features make it a likely descendant of A. africanus —one of Lucy's direct descendants — and either a direct ancestor of early Homo and ultimately us, or what Berger calls "a very close side branch."
"It sits at a very critical moment in time," said Berger. It "fills a critical gap in the line."
While the Australopithecus designation is correct, "the proposed link between A. sediba and early Homo is forced and tenuous at best," said William Jungers, a Stony Brook University paleoanthropologist. He doesn't consider a juvenile specimen — the most complete of the two skeletons comes from the human equivalent of a teenager — a reliable indicator of adult features.
To this criticism, Berger said the teen's brain had "clearly reached about 95 to 98 percent of adult capacity." Few changes would be expected in its cranial size and shape, which are critical in characterizing a primate species.
Jungers also noted that the first Homo fossils predate A. sediba by 500,000 years, while Homo ergaster had reached western Asia just 200,000 years after A. Sediba's known date. Both these figures suggest that Homo was established well before A. sediba came along, said Rick Potts, curator of anthropology at the Smithsonian National Museum of Natural History.
"The connection with the origin of Homo doesn't seem to hold much water," said Potts, and the confluence of some A. sediba traits with Homo is just coincidence. "Evolution produces a universe of features that are combined and recombined," he said.
According to Berger, however, A. sediba may have older roots than they think. "The site we found is simply a point in time. It doesn't represent the first appearance of this species," he said.
Meanwhile, Arizona State University paleoanthropologist William Kimbel argued that A. sediba should have been classified as Homo, though it may not have been a direct human ancestor.
"In my way of thinking, it belongs in Homo because of the brow ridge, the face, the pelvis," he said. "It's true that it has the small brain and long upper limbs indicative of Australopithecus, but those are signs of its ancestry, not its future."
These arguments may be settled as more A. sediba skeletons emerge. Berger is currently assembling at least two. However, taxonomical debates may ultimately prove less important than the questions A. sediba provokes.
Already the fossils suggest that Australopithecus didn't morph suddenly into Homo, but adapted in gradual, piecemeal fashion. What pressures led to these adaptations, and their relationship to tool use, cognitive developments, dietary shifts and climate changes, have yet to be determined.
"The significance is in the patterns and insights it provides," said Kimbel. "These specimens fall at the young end of a very puzzling million-year period in hominin evolution."
Whether or not A. sediba is our ancestor, "it could help us understand the dynamics that led to the split producing the lineage culminating ultimately in us," said Kimbel.
Images: Lee Berger/Science.
Citations: "Australopithecus sediba: A New Species of Homo-Like Australopith from South Africa." By Lee R. Berger, Darryl J. deRuiter, Steven E. Churchill, Peter Schmid, Kristian J. Carlson, Paul H. G. M. Dirks, Job M. Kibii. Science, Vol. 328 No. 5975, April 9, 2010.
"Geological Setting and Age of Australopithecus sediba from Southern Africa." By Paul H. G. M. Dirks, Job M. Kibii, Brian F. Kuhn, Christine Steininger, Steven E. Churchill, Jan D. Kramers, Robyn Pickering, Daniel L. Farber, Anne-Sophie Mériaux, Andy I. R. Herries, Geoffrey C. P. King, Lee R. Berger. Science, Vol. 328 No. 5975, April 9, 2010.
Posted: 07 Apr 2010 02:42 PM PDT
A mysterious object discovered near a brown dwarf doesn't fit into any known astronomical category.
The newly discovered mystery companion forms a binary system with the brown dwarf, located 460 light-years away in the Taurus star-forming system. The object is too light to be another brown dwarf, but it's too young to have formed by accretion, the way a typical planet does.
"Although this small companion appears to have a mass that is comparable to the mass of planets around stars, we don't think it formed like a planet," said astronomer Kevin Luhman of Penn State University, co-author of the study April 5 in The Astrophysical Journal. "This seems to indicate that there are two different ways for nature to make small companions."
Luhman's team made the discovery with the Hubble Space Telescope and the Gemini Observatory. The discovery was made using the Wide Field Planetary Camera 2 on the Hubble Space Telescope and the Gemini Observatory.
The new object and its companion brown dwarf are orbiting as a binary pair, 15 astronomical units from each other. If they were superimposed on our solar system, the companion would be orbiting midway between Saturn and Uranus. The oddball object's mass is somewhere between five and 10 Jupiter masses, making it too small to fuse deuterium. The International Astronomical Union currently uses this fusion line, which occurs at about 13 Jupiter masses, as the defining characteristic of a brown dwarf.
But the object appears to be around the same age as its binary partner, which doesn't fit conventional ideas about planet formation. Traditional theories describe planets forming from the gaseous disk that swirls around the equator of a newly formed star. Particles in the gas and dust cloud collide, and gradually accrete into larger objects, eventually becoming planets. These rocky planets can grow into sizes up to 10 Earth masses before they become gas giants.
And 1 million years is much shorter than the expected time for a planet to be born this way. Planets can form this quickly when there is a gravitational instability in the gaseous disk, but the brown dwarf's disk probably didn't have enough material to form a planet larger than a single Jupiter mass.
"It looks like this new system formed by the collapse and fragmentation process that forms binary star systems," Alan Boss, president of the IAU Commission on Extrasolar Planets said in an e-mail to Wired.com. Boss theorized that these sorts of planet-sized objects exist in a paper published in 2001.
"While people like to use the 'p-word' to describe objects with masses below 13 Jupiter masses, given the attention given to exoplanets these days, they should more properly be called 'sub-brown dwarfs,'" Boss said.
Because this strange object seems more likely to have formed the same way as its binary partner, the brown dwarf, Luhman believes it is probably best classified as a very small brown dwarf.
"This object, because it formed like a star, its composition is probably the same throughout," Luhman said. This homogenous composition is in stark contrast to the innards of gas giants, like Jupiter, which probably have a heavy-element rocky core surrounded by a gaseous shell composed mainly of hydrogen and helium.
The presence of another nearby binary system, of a red star and a brown dwarf, supports Luhman's theory. It seems to have been formed around the same time as the mystery pair, indicating that all four may have formed the same way, as stars.
"This configuration — two tight pairs that are widely separatedfrom each other — is called a hierarchical configuration and is commonlyseen in quadruple star systems," Luhman said.
Images: 1) NASA, ESA, K. Todorov, K. Luhman, Penn State University. 2) Artist's rendering fromGemini Observatory/L. Cook.
Posted: 07 Apr 2010 01:46 PM PDT
Even the bird-brained can follow a leader. When pigeons fly in flocks, each bird falls behind another with better navigational skill, and the savviest among them leads the flock, scientists report in the April 8 Nature.
The research suggests hierarchies can serve peaceful purposes in the animal kingdom, where dominance by brute force is often the rule. "A pecking order tends to be just that — a pecking order," says Iain Couzin of Princeton University, an expert in collective behavior who was not involved in the research.
The research also suggests that for pigeons, dominance isn't set in stone. While one bird often emerged as the leader, other birds also stepped up. This flexibility in leadership had previously been seen only in some small groups of fish.
From schools to packs to swarms to flocks, collective behavior is widespread among animals. But in many cases, the important interactions are with nearest neighbors, and control of the group's movement is distributed among members rather than hierarchical.
Biological physicist Tamás Vicsek of Eötvös Loránd University in Budapest and his colleagues studied flight dynamics in homing pigeons, which fly in flocks but conveniently return to their roosts. The researchers outfitted 13 pigeons with tiny backpacks carrying GPS devices that measured shifts in birds' flight direction five times per second. Flocks of eight to 10 birds flew with the devices during homing flights (a roughly 14-kilometer trip back to the roost) and spontaneous "free" flights near home. Each bird also flew solo flights of about 15 kilometers each.
Analysis of GPS logs showed that for each excursion, the flock had one leader followed by at least three or four other birds. Each of these followers was in turn followed by other birds in the flock. Comparing the solo flight paths to the group flights showed that the birds with the best navigational skills led the flock.
While flocks have hierarchies, they're not dictatorships, notes Vicsek. One bird led eight of the 13 flights, while other birds took the lead on the rest of the trips. Vicsek likens the dynamics to a group of peers deciding where to eat dinner. "Maybe someone knows the area restaurants best, or there is a person who's a gourmand — or maybe they are the most outspoken," he says. This one person might pick the place to eat for several nights, although another person might chime in now and then. And then there is the person with no say, whom everyone knows has terrible taste in food.
"These pigeons know each other. They know which is the smartest. The fastest bird will even follow the slower one who knows the way home the best," say Vicsek. Videos of the birds' positions during flight showed that if the best navigator moves a little to the left, it takes about a third of a second for other birds to do the same. But if the least savvy bird makes a move "the others don't care," Vicsek says.
Pigeons' brains may be wired for follow-the-leader, comments behavioral neuroscientist Lucia Jacobs of the University of California, Berkeley. When the left eye sees something, for example, it sends all the visual information to the right brain hemisphere, and vice versa. This "extreme lateralization" may play a role in organizing flocks, the new work suggests. A pigeon following another was most likely to be flying on its partner's right, seeing this leader with its left eye. "It's very cool," Jacobs says.
Images: Zsuzsa Ákos
Posted: 07 Apr 2010 01:05 PM PDT
In the muck of the deep Mediterranean seafloor, scientists have found the first multicellular animals capable of surviving in an entirely oxygen-free environment.
Some types of bacteria and other single-celled organisms can live without oxygen, but nothing as complex had been found as these three species of Loricifera, a group of marine-sediment dwellers who inhabit one of Earth's most extreme and little-known environments.
"The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen," wrote researchers led by Roberto Danovaro, a marine biologist at Italy's Polytechnic University of Marche, in a study published April 6 in BMC Biology.
The new species, however, don't have the mitochondria found in almost every other animal cell, converting oxygen and nutrients into chemical energy.
Even the few parasite species once thought to be mitochondria-free seem to have had them at some point in history, and possess mitochondrial remnants that perform the same essential functions.
Instead the new Loricifera species have structures called hydrogenosomes, which are found in some single-celled organisms and require no oxygen to produce chemical energy.
The evolutionary history of these creatures is not known, but they live in an environment reminiscent of Earth's oceans some 600 million years ago, before the deep seas were oxygenated and large animals evolved, wrote Comenius University (Slovakia) biochemist Marek Mentel and Düsseldorf University (Germany) biologist William Martin in an accompanying commentary.
These "fascinating animals" provide a "glimpse of what a good part of Earth's past ecology might have been like," they wrote.
Image: Roberto Danovaro/BMC Biology.
Citations: "The first metazoa living in permanently anoxic conditions." By Roberto Danovaro, Antonio Dell'Anno, Antonio Pusceddu, Cristina Gambi, Iben Heiner and Reinhardt Mobjerg Kristensen. BMC Biology, Vol. 8 No. 32, April 6, 2010.
"Anaerobic animals from an ancient, anoxic ecological niche." By Marek Mentel and William Martin. BMC Biology, Vol. 8 No. 32, April 6, 2010.
Posted: 07 Apr 2010 10:29 AM PDT
Scientists couldn't see the lizard for the trees.
In forests on the Philippine island of Luzon, the newly discovered monitor lizard hauls itself up into trees in search of fruit and melts into the vegetation if humans approach, says herpetologist Rafe Brown of the Biodiversity Institute at the University of Kansas in Lawrence. He and his colleagues describe and name the species in paper published online the week of April 5 in Biology Letters.
The species is "new to us," Brown clarifies, because the Agta and Ilongot peoples living in forests of the Sierra Madre range know the lizard well — as a delicacy. It mostly eats fruit and reportedly tastes better than a much more common scavenging monitor that's "attracted to stinky stuff," Brown says.
A cousin to the giant Komodo dragon, Varanus bitatawa is hard to find but once detected, is pretty hard to ignore. During adulthood, yellow markings differentiate it from a much drabber neighbor — though both species sport colorful patterns as juveniles.
Reptile systematist Michael B. Harvey, who was not part of Brown's group, has helped name another Varanus lizard from New Guinea and examined specimens from Southeast Asia. "I quickly realized that diversity of these lizards had been greatly underestimated," says Harvey, of Broward College in Davie, Florida. "I only hope that we don't lose much of this biodiversity before scientists can study it."
Deforestation poses a major threat to the biodiversity of the Philippines, which Brown and his colleagues describe in their paper as a "global conservation hot spot."
Western scientists first glimpsed the big monitor in 2001, Brown says, when biologists exploring the forest happened on hunters carrying a large lizard home for dinner. The biologists were permitted to photograph it, but theirs was the first of several encounters in which hunters showed no interest in giving up the centerpiece of a big family meal.
Herpetologist Arvin Diesmos of the National Museum of the Philippines in Manila and other researchers persisted in collecting photographs, local intelligence and the occasional juvenile, but they could not secure a full-grown adult specimen.
Then, in the summer of 2009, a team led by Brown and his graduate student Luke Welton got its hands on an adult lizard. They documented identifying anatomical characteristics such as the distinctive little horns on the ends of the lizards' double-barreled male reproductive organs. Which, by the way, are far from unusual in and of themselves: "All snakes and lizards have a paired copulatory organ," Brown says.
DNA tests were even more important, confirming that the species differs from a previously identified fruit-eating monitor living in a different part of the island.
Brown actually learned of the adult specimen's existence via text message. After he and his students spent weeks in the mountains surveying other vertebrates and hoping for an adult Varanus bitatawa, Brown had to return home early to start the fall semester. But he received a message from his students in the expedition's final hours announcing their success — and letting him know that they were having a hard time finding a way to get from their camp to the airport.
Posted: 07 Apr 2010 10:00 AM PDT
The old adage, "You are what you eat," has a bacterial component.
In a neat confluence of human history, stomach bacteria and food, researchers have found that the intestinal microbes of Japanese people may be souped up for eating seaweed.
"In a marine bacteria, we identified an enzyme that is very specialized for degrading algal cell walls," said Mirjam Czjzek, a biologist at France's Station Biologique de Roscoff. "The only other place we find this enzyme is in the human-gut bacteria of Japanese individuals."
The discovery, described April 7 in Nature, started with Roscoff biologist Jan-Hendrik Hehemann's analysis of Zobellia galactanivorans, a common marine bacteria. In it, he found an enzyme that breaks down porphyran, a carbohydrate found in the cell walls of red algae.
The gene that codes for the enzyme has been found in one other place: the genome of Bacteroides plebeius, a microbe found in human intestines. However, not all B. plebeius strains produce the algae-crunching enzyme. It has only been found in Japanese people.
According to the researchers, the enzyme helps Z. galactanivorans eat red algae, which westerners know best as the nori seaweed wrapping around sushi rolls. At some unknown points and in some unknown stomachs in the Japanese past, the enzyme-coding gene passed from Z. galactanivorans and into B. plebeius. That lucky microbe would have benefited from a new-found ability to process red algae, spreading through its stomach environment and eventually through the human population, which in turn derived more nutrients from an algae-rich diet.
Humans are known to benefit from digestive enzymes produced by the trillions of microbes in each person's intestines, but "I don't think anyone's ever shown an ethnic difference like this," said Andrew Gewirtz, an Emory University immunologist who studies the role of gut bacteria in obesity. "It's perfectly logical, and fits with ideas that scientists have kicked around."
How much the new gene helps people digest seaweed hasn't yet been quantified. The microbes' fate in people with seaweed-free diets is uncertain.
The researchers also don't know when the gene jumped from marine to human microbes, though Czjzek suspects it happened long ago. As for whether other people have seaweed-processing strains, the study isn't absolutely conclusive. It looked only at the gut microbes of 18 westerners — enough to suggest a pattern, but not a final word, though the chances are probably low.
"Often the question comes, 'I've been eating sushi for two years now. Do I have this enzyme?' The answer is, these are very rare events," said Czjzek. "In the early days, seaweed wasn't sterilized. Nowadays, it's cooked, roasted and prepared. The chance to have this type of transfer is much lower."
That's likely the case with most types of food, said Gewirtz. As for whether "that's a good or a bad thing, it's hard to say," he said. But Justin Sonnenburg, a Stanford University microbiologist who wrote a commentary accompanying the findings, is concerned.
"Consumption of hyper-hygienic, mass-produced, highly-processed and calorie-dense foods is testing how rapidly the microbiota of individuals in industrialized countries can adapt while being deprived of the environmental reservoirs of microbial genes," he wrote.
However, globalized diets do give people a chance to eat foods they wouldn't have found before. "The next time you take a bite of an unfamiliar food, think about the microbial inhabitants you may also be ingesting, and the possibility that you will be providing one of your 10 trillion closest friends with a new set of utensils," wrote Sonnenburg.
Image: Javier Lastras/Flickr.
Citations: "Transfer of carbohydrate-active enzymes from marine bacteria to Japanese gut microbiota." By Jan-Hendrik Hehemann, Gaelle Correc, Tristan Barbeyron, William Helbert, Mirjam Czjzek, & Gurvan Michel. Nature, Vol. 464 No. 7290, April 8, 2010.
"Genetic pot luck." By Justin L. Sonnenburg. Nature, Vol. 464 No. 7290, April 8, 2010.
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