News and notes about science
Even hermit crabs have wealth inequality
Hermit crabs face a uniquely competitive real estate market. They need bigger and bigger shells throughout their lives, but can’t grow these homes themselves. So they rely on castoff snail shells and are constantly on the lookout for better properties entering the market.
A study that will be published in January in the journal Physica A found that the distribution of these shells in one hermit crab population was surprisingly similar to the distribution of wealth in human societies.
That may make hermit crabs one of the first animals known to experience wealth inequality.
Ivan Chase, an emeritus professor at Stony Brook University in New York and the study’s lead author, researches social systems in animals and described a phenomenon called the vacancy chain in hermit crabs in the 1980s.
When a snail dies on the beach, a crab that comes across the empty shell will inspect it closely, turning the shell over in its claws. If the crab decides this home is better than its current shell, it trades up. Another, usually smaller crab may soon find that crab’s castoff and move in. Each vacancy lets about three crabs upgrade their shells, Chase said.
The team used a number called the Gini coefficient to measure overall inequality among the crabs. It found a value similar to that in small human populations, though not as great as in today’s large countries. The top 1 percent of hermit crabs owned only about 3 percent of the total shell weight, Chase and his coauthors noted: “There are no Warren Buffetts or Jeff Bezoses.” There is also no transfer of shells between crabs and their offspring.
“Vacancy chains are just another way of transferring property,” he said. Elizabeth Preston
NASA’s Osiris-Rex selects target asteroid landing site
A landing pad fit for a visitor from NASA has been found on an ancient relic of our solar system.
NASA’s Osiris-Rex spacecraft left Earth in 2016, its sights set on an asteroid named Bennu that is as wide as the Empire State Building is tall. The robotic probe’s mission is to collect a sample from the surface of this space rock and bring it home to our planet, helping scientists understand more about the nascent days of our solar system.
But first the spacecraft’s controllers on Earth had to find a place for Osiris-Rex to land. On Thursday they announced their target site. Named Nightingale, the area is near Bennu’s north pole and lies inside a small crater within a larger crater.
“We made our final decision based on which site has the greatest amount of fine-grained material and how easily the spacecraft can access that material while keeping the spacecraft safe,” said Dante Lauretta, the mission’s principal investigator and a planetary scientist at the University of Arizona in Tucson.
Lauretta also said the site’s scientific value was high because of the northern latitude. Colder temperatures there mean more of the material the spacecraft collects could be preserved from when the asteroid first formed.
Osiris-Rex will only land on the surface of Bennu for a split second next year, deploying an arm , called Tagsam, to quickly snatch a sample before heading back to a safe distance.
“This is going to be very very challenging; we are pushing the spacecraft to do things it was not designed to do,” said Lori Glaze, the director of NASA’s planetary science division.
To that end, she said the mission’s managers are improving Osiris-Rex’s software so it can better navigate the terrain it will encounter. Shannon Stirone
Head cones in ancient Egyptian graves cap archaeological debate
Painted throughout ancient Egyptian hieroglyphics are scenes of people at boisterous banquets. On top of the dark, braided heads of some revelers sit peculiar white cones. Archaeologists have long puzzled over the purpose of the mysterious headgear and whether they were real items worn by people, or just iconographic ornaments, like halos crowning saints in Christian artwork.
Now, a team of archaeologists has uncovered — for the first time — two of the “head cones” in the ancient Egyptian city of Amarna, nearly 200 miles south of Cairo. The cones were made of wax and dated from 1347 to 1332 B.C. when Egypt was ruled by the pharaoh Akhenaten. The finding, which was published in the journal Antiquity, provides the first evidence the cones were actual objects and indicates they served some funerary function.
Corina Rogge, a conservation scientist from the Museum of Fine Arts, Houston, and an author on the study, said it was very satisfying “to finally be able to say that the head cones
are real.”
Some archaeologists have argued that the main role of the cones, which have been featured on tomb walls from the Eighteenth Dynasty around 1550 B.C. through the time of Cleopatra, was to act as perfumed unguents. Under the intense Egyptian heat, the scented wax cone would melt into the wearer’s hair or wig, providing a sweet aroma to the wearer. So far, the team’s findings do not confirm that interpretation, and alas, hieroglyphics are not scratch-and-sniff. Nicholas St. Fleur
What a 5,700-year-old wad of chewed gum reveals about ancient people and their bacteria
When hunter-gatherers living in what is now southern Denmark broke down pieces of birch bark into sticky, black tar about 5,700 years ago, they almost certainly didn’t realize that they were leaving future scientists their entire DNA.
Ancient people used the gooey birch pitch to fix arrowheads onto arrows and to repair a variety of stone tools. When it started to solidify, they rolled the pitch in their mouths and chewed on it, like some sort of primitive bubble gum. Chewing on birch pitch would have made it pliable again for using on tools.
It might have also relieved toothaches because of the antiseptic oils in the gum. It’s possible that children also used it recreationally, much like modern humans do today. When they spat the gum out, the same antiseptic properties helped preserve the DNA in their saliva.
The ancient DNA, described in a paper published in Nature Communications, is especially valuable because few human bones from the Mesolithic and Neolithic stone ages have been found in Scandinavia. DNA from the chewed-up gum provides clues about the people who settled in the area, the kind of food they ate and even the type of bacteria they carried on their teeth.
“This is a snapshot of a real person in real time,” said Natalija Kashuba, an archaeologist at Uppsala University in Sweden, who also studies birch pitch samples but was not involved in the latest research. “It’s as close as we’ll ever come to standing face to face with an individual from the Stone Age of Scandinavia.” Knvul Sheikh
Boulders don’t just roll — they bounce
There’s a place in Chile’s Atacama Desert where trails of depressions punctuate the fine chusca dust. But what might seem like the footsteps left by a giant creature are, in fact, exquisitely preserved evidence of boulders that tumbled down a nearby cliff face before bouncing to their final resting place.
The site, the Chuculay Boulder Field, is home to thousands of granite goliaths, some as big as houses. And because the desert’s hyperarid conditions preserve the boulders’ steps, it’s “an ideal place to study rockfall theory and physics,” said Paul Morgan, a geologist at Cornell University.
Morgan and his collaborators analyzed the trajectories of some of these boulders and presented their research at the American Geophysical Union conference in San Francisco. Their findings of how far boulders tumble are useful for designing structures that could protect people and property in rockfall-prone areas.
To map the boulders and the scarp in three dimensions, the research team scanned them with quadcopter drones equipped with cameras. They also scrambled up the scarp one day to get their own view.
“It was on the edge of safe,” Morgan said.
When the researchers analyzed the locations of the impact craters, they were surprised. They had expected that the distances between successive depressions would decrease as the bouncing rocks lost energy.
“But sometimes there was a short bounce followed by a long bounce,” said Morgan.
One explanation is that natural variations in the properties of the desert floor — its slope and composition, for instance — affected how the rocks bounced. Another possibility is that some of the boulders broke apart, and that the craters left behind recorded the bounces of different fragments. Katherine Kornei