December 5, 2013
The magnitude 9.0 Tohoku-Oki earthquake that struck Japan on 11 March 2011, killing more than 15,000 people and setting off a devastating tsunami that the nation is still working to recover from, brought up a lot of troubling questions. For instance,
what made such a powerful earthquake possible, and could it happen again in Japan or somewhere else?
An international group of scientists that drilled miles beneath the Pacific Ocean and into the earthquake fault now have answers to these questions, and they report their findings in a trio of papers published today in Science.
The epicenter of the 2011 quake was in an unusual spot, about 130 kilometers east of Sendai, Japan, just off the northern coast of that nation
. In this area, a subduction zone, the Pacific plate is diving beneath the Eurasian plate. Strong earthquakes are possible here, but scientists hadn’t thought that there was enough energy to produce one larger than magnitude 7.5. They were wrong, and they’ve been interested in finding out more about what made the fault capable of producing such a large quake.
A little over a year after the earthquake, the deep sea drilling vessel Chikyu was tasked with the mission to drill into the fault off the Japanese coast and install a temperature observatory. By taking the temperature of a fault after an earthquake, scientists can measure how much energy was released in the quake and calculate a fault’s friction—how easily the rocks rub against each other.
“One way to look at the friction of these big blocks is to compare them to cross-country skis on snow,” Robert Harris, a study co-author and geophysicist at Oregon State University, said in a statement. “At rest, the skis stick to the snow and it takes a certain amount of force to make them slide. Once you do, the ski’s movement generates heat and it takes much less force to continue the movement…. The same thing happens with an earthquake.”
Getting that temperature measurement was tricky. The Chikyu team had to drill 850 meters into the seafloor, which itself was 6,900 meters below the ocean’s surface. They had to deal with bad weather, and the fault itself was still shifting, putting the instruments at risk.
The difficult work paid off, though, and it revealed residual heat from the earthquake, from which the scientists could calculate the fault’s friction, which was very low. Bottom line: “The Tohoku fault is more slippery than anyone expected,” Emily Brodsky, a study co-author and geophysicist at the University of California, Santa Cruz, said in another statement.
The slippery nature of the fault helps to explain some characteristics of the 2011 quake. The fault slipped an unprecedented 50 meters and the rupture, which began deep underground, reached the surface where it caused a sudden disturbance in the ocean and set off the tsunami.
The drilling and laboratory tests also revealed another characteristic of the fault that made it so dangerous. The low friction can be attributed to incredibly fine clay sediment within the fault. “It’s the slipperiest clay you can imagine,” Christie Rowe, a study co-author and geologist at McGill University, said in a statement. “If you rub it between your fingers, it feels like a lubricant.” Incidentally, the area between the Pacific and Eurasian plates that experiences slip is also very thin, less than five meters across, which would make it the thinnest known fault zone on the planet.
Measuring the earthquake’s thermal signal was a first for science. It “was a major accomplishment,” Harris said, “but there is still a lot we don’t yet know.” For example, researchers don’t yet know how generalizable these results are to other subduction zones across the world or what effect the thinness of fault zones has on earthquake hazards. Nonetheless, the drilling results “suggest that the shallow megathrust at the Japan Trench has special traits not seen in many other subduction zones,” Kelin Wang of Natural Resources Canada and Masataka Kinoshita of the Japan Agency for Marine-Earth Science and Technology—the agency that runs the Chikyu—wrote in an accompanying Perspectives article.
Similar conditions may be rare, but they do exist in some places of the north Pacific, such as the Kamchatka Peninsula in Russia and the Aleutian Islands in Alaska, notes Rowe.Deep sea drilling shows that these regions have that same usually slippery clay that lowered the friction in the Japan fault.
But the fact that the unusual circumstances of the Japan fault may be rare shouldn’t put scientists, or the public, at ease, Wang and Kinoshita say. Such huge, shallow slip isn’t necessary for a devastating tsunami to form, and it wasn’t what caused either the 2010 Chile tsunami that destroyed 370,000 homes or the 2004 Indian Ocean tsunami that killed nearly 230,000 people. “It’s hard to say how generalizable these results are until we look at other faults,” Brodsky added. “But this lays the foundation for a better understanding of earthquakes and, ultimately, a better ability to identify earthquake hazards.”
December 4, 2013
Since its discovery in 1990, La Sima de los Huesos, an underground cave in Northern Spain’s Atapuerca Mountains, has yielded more than 6,000 fossils from 28 individual ancient human ancestors, making it Europe’s most significant site for the study of ancient humans. But despite years of analysis, the exact age and even the species to which these individuals belonged has been in doubt.
Now, though, an international group of scientists has extracted and sequenced DNA from the fossilized femur of one of these individuals for the first time. The resulting data—which represent the oldest genetic material ever sequenced from a hominin, or ancient human ancestor—finally give us an idea of the age and lineage of these mysterious individuals, and it’s not what many scientists expected.
The fossilized bone tested, a femur, is roughly 400,000 years old. But the big surprise is that, although scientists had previously believed the fossils belonged to Neanderthals because of their anatomical appearance, the DNA analysis actually shows they’re more closely related to Denisovans, a recently-discovered third lineage of human ancestors known only from DNA isolated from a few fossils found in Siberia in 2010. The findings, published today in Nature, will force anthropologists to further reconsider how the Denisovans, Neanderthals and the direct ancestors of modern-day humans fit together in a complicated family tree.
The analysis was enabled by recent advances in methods for recovering ancient DNA fragments developed at the Max Planck Institute for Evolutionary Anthropology in Germany, previously used to analyze the DNA of a cave bear fossil found in the same cave. “This wouldn’t have been possible just two years ago,” says Juan Luis Arsuaga, a paleontologist at the University of Madrid who led the initial excavations of the cave and collaborated on the new study. “And even given these new methods, we still didn’t expect these bones to preserve DNA, because they’re so old—ten times older than some of the oldest Neanderthals from whom we’ve taken DNA.”
After extracting a two grams of crushed bone from the femur, a group of scientists led by Matthias Meyer isolated the mitochondrial DNA (mtDNA), a pool of genetic material that’s distinct from the DNA in the chromosomes located in our cells’ nuclei. Instead, this mtDNA lives in our cells’ mitochondria—microscopic organelles responsible for cellular respiration—and is much shorter in length than nuclear DNA.
There’s another quirk of mtDNA that makes it especially valuable as a means of studying the evolution of ancient humans: Unlike your nuclear DNA, which is a mix of DNA from both your parents, your mtDNA comes solely from your mother, because most of a sperm’s mitochondria are found in its tail, which it sheds after fertilization. As a result, mtDNA is nearly identical from generation to generation, and a limited number of distinct sequences of mtDNA (called haplogroups) have been observed in both modern humans and ancient human ancestors. Unlike anatomical characteristics and nuclear DNA, which can vary within a group and make it difficult to confidently distinguish one from another, mtDNA is generally consistent, making it easier to link a particular specimen with a lineage.
Which is why, when the researchers compared the femur’s mtDNA to previously sequenced samples from Neanderthals, from a Denisovan finger bone and tooth found in Siberia and from many different modern humans, they found it so surprising that it more closely resembled the Denisovans. “This was really unexpected,” Arsuaga says. “We had to think really hard to come up with a few scenarios that could potentially explain this.”
Anthropologists had already known that all three lineages (humans, Neanderthals and Denisovans) shared a common ancestor, but it’s far from clear how all three groups fit together, and the picture is further clouded by the fact that interbreeding may have occurred between them after they diverged. Helpfully, comparing the femur’s mtDNA to the Neanderthal, Denisovan and modern human samples allowed the researchers to estimate its age—based upon known rates of mtDNA mutation, the previously established ages of the other samples, and the degree of difference between them—leading to the 400,000 year figure.
To explain how a Neanderthal-looking individual could come to have Denisovan mtDNA during this time period, the scientists present several different hypothetical scenarios. It’s possible, for instance, that the fossil in question belongs to a lineage that served as ancestors of both Neanderthals and Denisovans, or more likely, one that came after the split between the two groups (estimated to be around 1 million years ago) and was closely related to the latter but not the former. It’s also a possibility that the femur belongs to a third, different group, and that its similarities to Denisovan mtDNA are explained by either interbreeding with the Denisovans or the existence of yet another hominin lineage that bred with both Denisovans and the La Sima de los Huesos population and introduced the same mtDNA to both groups.
If this sounds like a complicated family tree to you, you’re not alone. This analysis, along with earlier work, adds further mystery to an already puzzling situation. Initial testing on the Denisovan finger bone found in Siberia, for instance, found that it shared mtDNA with modern humans living in New Guinea, but nowhere else. Meanwhile, it was previously thought that Neanderthals had settled in Europe and Denisovans further east, on the other side of the Ural Mountains. The new analysis complicates that idea.
For now, the researchers believe the most plausible scenario (illustrated below) is the femur belongs to a lineage that split off from Denisovans sometime after they diverged from the common ancestor of both Neanderthals and modern humans. But perhaps the most exciting conclusion to come out of this work is that it proves that genetic material can survive for at least 400,000 years, and can be analyzed even after that amount of degradation. Armed with this knowledge and the new techniques, anthropologists can now attempt to genetically survey many other ancient specimens in hopes of better understanding our family tree.
In 1917, British artist Norman Wilkinson experienced a eureka moment while serving in the Royal Naval Volunteer Reserve. Throughout the month of April, German U-boats had been mercilessly torpedoing British ships, sending around eight of those vessels per day into the watery abyss. Hiding a ship traveling on the open ocean from plain sight was impossible, Wilkinson knew, but a bit of artistic trickery may be able to muddle the Germans’ ability to accurately judge the exact location of that ship, he realized.
From that idea, Wilkinson devised a type of camouflage called “razzle dazzle” (its slightly more serious name is dazzle camouflage). The technique consists of squashing together contrasting geometric patterns, shapes and colors to create a pattern of optics that would confuse enemies by distorting the object’s dimensions and boundaries. All in all, more than 2,000 ships received such a makeover, although the scheme’s effectiveness seemed to produce mixed results.
By World War II, razzle dazzle had largely fallen out of favor, but as it turns out, this technique lives on in the natural world. High contrast patterns–nature’s equivalent to dazzle camouflage–are used by animals ranging from snakes to zebra to fish. Like those hidden World War I ships, many creatures seem to use dazzle patterns to conceal themselves from predators. Until now, however, researchers hadn’t considered the flipside of this relationship: could predators use razzle dazzle to sneak up on prey as they mounted an attack?
To investigate this possibility, biologist Roger Santer of Aberystwyth University in the U.K. turned to locusts. These insects are particularly well suited for vision studies due to something called a single lobula giant movement detector neuron, a unique cell that specializes in detecting looming objects (think of a car speeding towards you, or a hand reaching for your face). Researchers think this neuron works by measuring the shape and movement of patterns of light and dark across the eye. Whatever the mechanism, as looming objects approach a locust, its detector neuron fires away, alerting the insect to imminent potential danger and triggering it to flee.
To see how the locusts responded to dazzle camouflage, Santer created an array of visual patterns using a graphics software. He situated the locusts just in front of the computer monitor, and then projected a simulated approach of those objects from about 10 meters away to about 0.07 meters from the cowering insects. The objects varied in contrast: black, grey or white on a grey background. Around 20 locusts took part in the experiment, and Santer measured their cellular reactions to the various shapes through copper wires inserted into the locusts’ neck.
The locusts’ neurological responses to the looming objects depended on which patterns they saw, Santer reports in Biology Letters. Squares with both a darker-than-background top and bottom half elicited the strongest panic response, followed by squares with a dark upper half, but a bottom half that was the same color as the background. Squares that had an upper half that was dark but a bottom half that was bright (in other words, the razzle dazzle ones) produced a significantly weaker panic response, as did squares that were brighter than the background. Finally, squares that were the same color as the background produced no response at all.
These results are interesting in that they correlate with similar dazzle tests performed on humans, who also had trouble quickly registering dazzle patterns. However, at this point, whether or not locust predators actually use dazzle to catch their unsuspecting insect prey remains a matter of speculation. Though lab tests confirm this strategy might work, Santer did not investigate whether or not a dazzle dance of death is carried out in the real world.
Hypothetically speaking, dazzle camouflage, Santer concludes, would help a predator but would not be the most effective way of snagging a locust lunch. Instead, classic camouflage–blending in with the background rather than creating an optical illusion–seems to be the most effective means of tricking would-be prey. However, in the case that other selection pressures favor high-contrast patterns (such as if females of a predator species prefer bold stripes in males), Santer thinks that predators could indeed evolve to give ‘em the old razzle dazzle.
December 3, 2013
Scientific equipment that’s left unattended in the field can provide all sorts of interesting information. It can, for instance, snap photographs of exotic and shy wild animals, or analyze the noises coming from an ecosystem to identify the species living there.
But often, leaving valuable instruments scattered outside risks interference or destruction from an unavoidable force of nature: humans. Data isn’t regularly collected or published on the topic, but it’s well known among field scientists that leaving equipment in highly-trafficked areas leaves it vulnerable to petty vandalism and theft.
This unfortunate trend was recently on the mind of Holger Goerlitz, a scientist at Germany’s Max Planck Institute for Ornithology who studies animal behavior (specifically, how bats use echolocation within their environment) and leaves his field equipment unattended to do so. “As part of a project, I wanted to deploy automated equipment that would sit in the field for several nights,” he says. “So my colleagues and I were concerned about how to protect this equipment. We considered using chains and video cameras. And then suddenly we had this random idea: Let’s see what would be a good label to attach to the equipment to reduce vandalism.”
His team’s results, based on 60 pieces of fake scientific equipment scattered in four different Munich parks and published last week in Methods in Ecology and Evolution, may surprise you. They found that friendly labels that gave information about the project and the researcher led to about 40 percent fewer instances of equipment interference—either theft, vandalism or park visitors simply moving or trying to open up the equipment—as compared to neutral labels or ones that threatened surveillance and punishment.
They found this out by distributing boxes that looked vaguely like scientific instruments (above)—basically, plastic boxes with car antennas and fake cameras attached—for one week in each park, right next to a footpath, and checking for interference with the objects daily. All of the boxes had a similar warning label identifying it as properly of the Planck Institute and giving Goerlitz’ contact information, but the tone of the messages differed slightly.
A third of the boxes had neutral messages (translated to English, they read “Part of an experiment—Please do not touch”), while another third had threatening warnings (“‘Part of an experiment—Every theft will be reported to the police! GPS monitored!”) and the remaining third had a friendly, personalized note (“Part of my thesis–Please do not touch–Please call me if you have any questions and would like to know more.”) The friendly label also had a picture of a juvenile squirrel, to give passersby an idea of the researcher’s work:
The researchers checked the boxes daily, and had even placed pebbles inside so they could determine if the boxes had been picked up and moved. They also counted how many were pried open, vandalized or stolen.
Apparently, at least in these German city parks, the impulse to steal or vandalize is one that can be dislodged by just a bit of information about the potential victim, presented in a friendly way. Simply knowing that the device was important to one particular researcher—likely a student, given the word “thesis”—led visitors to interfere with the equipment about half as frequently. Over the course of a month, 39 instances of interference occurred with a box with a friendly label, compared to 59 with a neutral label and 67 with a threatening label.
Although the researchers were heartened by the finding, they were surprised, especially due to the fact that the threatening labels were the least successful. They imagine that the friendly label worked primarily by establishing the personal connection, perhaps aided by the squirrel photo, but the threatening label’s ineffectiveness is a mystery. “We don’t know why this was the case,” Goerlitz says. “It could be that people didn’t believe the threatening label, or that they thought, ‘oh, there’s a GPS device inside, this could be valuable.’” The fact that it was the only label that included the word “theft” might indicate that simply implanting the idea in people’s minds influenced them to engage in it.
But, although there’s obviously a lot more work to be done—this was conducted with a small sample of people over a short time period in one particular German city—this finding about friendly labels is a positive and potentially helpful one. If presented with the chance, people can be influenced to help science succeed if they’re treated in a respectful way and informed about what’s going on. Despite the enormous amount of money spent annually on scientific equipment, very little research has actually been done in this area to date, and more work to see how this might apply to people in different cultures, for instance, may aid scientists around the world in their efforts to protect their surveying instruments.
Goerlitz, for one, is ready to start using this finding to better safeguard his own equipment that monitors bat echolocation. “In my labels, I’ll try to be informative and friendly to people,” he says. “I think if you expose people to what you’re doing, they’ll be much more supportive of it.”
December 2, 2013
It’s a platitude that we’ve all heard dozens of times, whether to justify our treatment of other species or simply to celebrate a carnivorous lifestyle: humans are the top of the food chain.
Ecologists, though, have a statistical way of calculating a species’ trophic level—its level, or rank, in a food chain. And interestingly enough, no one ever tried to rigorously apply this method to see exactly where humans fall.
Until, that is, a group of French researchers recently decided to use food supply data from the U.N Food and Agricultural Organization (FAO) to calculate human tropic level (HTL) for the first time. Their findings, published today in the Proceedings of the Natural Academy of Sciences, might be a bit deflating for anyone who’s taken pride in occupying the top position.
On a scale of 1 to 5, with 1 being the score of a primary producer (a plant) and 5 being a pure apex predator (a animal that only eats meat and has few or no predators of its own, like a tiger, crocodile or boa constrictor), they found that based on diet, humans score a 2.21—roughly equal to an anchovy or pig. Their findings confirm common sense: We’re omnivores, eating a mix of plants and animals, rather than top-level predators that only consume meat.
To be clear, this doesn’t imply that we’re middle-level in that we routinely get eaten by higher-level predators—in modern society, at least, that isn’t a common concern—but that to be truly at the “top of the food chain,” in scientific terms, you have to strictly consume the meat of animals that are predators themselves. Obviously, as frequent consumers of rice, salad, bread, broccoli and cranberry sauce, among other plant products, we don’t fit that description.
The researchers, led by Sylvain Bonhommeau of the French Research Institute for Exploitation of the Sea, used FAO data to construct models of peoples’ diets in different countries over time, and used this to calculate HTL in 176 countries from 1961 to 2009. Calculating HTL is fairly straightforward: If a person diet is made up of half plant products and half meat, his or her trophic level will be 2.5. More meat, and the score increases; more plants, and it decreases.
With the FAO data, they found that while the worldwide HTL is 2.21, this varies widely: The country with the lowest score (Burundi) was 2.04, representing a diet that was 96.7 percent plant-based, while the country with the highest (Iceland) was 2.54, reflecting a diet that contained slightly more meats than plants.
On the whole, since 1961, our species’ overall HTL has increased just slightly—from 2.15 to 2.21—but this averaged number obscures several important regional trends.
A group of 30 developing nations in Southeast Asia and Sub-Saharan Africa (shown in red)—including Indonesia, Bangladesh and Nigeria, for example—have had HTLs below 2.1 during the entire period. But a second group of developing countries that includes India and China (shown in blue) has slightly higher HTL measures that have consistently risen over time, going from around 2.18 to over 2.2. The HTLs of a third group, shown in green (including Brazil, Chile, South Africa and several countries in Southern Europe), have risen further, from around 2.28 to 2.33.
By contrast, HTL in the world’s wealthiest countries (shown in purple)—including those in North America, Northern Europe and Australia—was extremely high for most of the study period but decreased slightly starting during the 1990s, going from around 2.42 to 2.4. A fifth group of small, mostly island countries with limited access to agricultural products (shown in yellow, including Iceland and Mauritania) has seen more dramatic declines, from over 2.6 to less than 2.5.
These trends closely correlate, it turns out, with a number of World Bank development indicators, such as gross domestic product, urbanization and education level. The basic trend, in other words, is that as people become wealthier, they eat more meat and fewer vegetable products.
That has translated to massive increases in meat consumption in many developing countries, including China, India, Brazil and South Africa. It also explains why meat consumption has leveled off in the world’s richest countries, as gains in wealth leveled off as well. Interestingly, these trends in meat consumption also correlate with observed and projected trends in trash production—data indicate that more wealth means more meat consumption and more garbage.
But the environmental impacts of eating meat go far beyond the trash thrown away afterward. Because of the quantities of water used, the greenhouse gases emitted and the pollution generated during the meat production process, it’s not a big leap to speculate that the transition of huge proportions of the world’s population from a plant-based diet to a meat-centric one could have dire consequences for the environment.
Unfortunately, like the garbage problem, the meat problem doesn’t hint at an obvious solution. Billions of people getting wealthier and having more choice over the diet they eat, on a basic level, is a good thing. In an ideal world, we’d figure out ways to make that transition less damaging while still feeding huge populations. For example, some researchers have advocated for offbeat food sources like meal worms as a sustainable meat, while others are trying to develop lab-grown cultured meat as an environmentally-friendly alternative. Meanwhile, some in Sweden are proposing a tax on meat to curb its environmental cost while government officials in the UK are urging consumers to cut back on their demand for meat to increase global food security and to improve health. Time will tell which approaches stick.
In the meantime, simply keeping track of the amount of meat we’re eating as a society via HTL could provide a host of useful baseline information. As the authors write, “HTL can be used by educators to illustrate the ecological position of humans in the food web, by policy makers to monitor the nutrition transition at global and national scales and to analyze the effects of development on dietary trends, and by resource managers to assess the impacts of human diets on resource use.”
In other words, monitoring the intricacies of our middling position on the food chain may yield scientific fodder to tackle problems like food security, obesity, malnutrition and environmental costs of the agricultural industry. A heavy caseload for a number that ranks us on the same trophic level as anchovies.