Murder was a calculated family affair among Iceland’s early Viking settlers. And the bigger the family, the more bloodthirsty.

Data from three family histories spanning six generations support the idea that disparities in family size have long influenced who killed whom in small-scale societies. These epic written stories, or sagas, record everything from births and marriages to deals and feuds.

Iceland’s Viking killers had on average nearly three times as many biological relatives and in-laws as their victims did, says a team led by evolutionary psychologist Robin Dunbar of the University of Oxford. Prolific killers responsible for five or more murders had the greatest advantage in kin numbers, the scientists report online September 20 in Evolution and Human Behavior.
Particularly successful killers chose their victims carefully, knowing that their large families would deter revenge attacks by smaller families of the slain, the researchers contend. Those killings were motivated by land grabs, they suspect. One-time killers tended to have only slightly bigger families than those of their victims; insults or goading possibly prompted those murders.
Strikingly, around 18 percent of all men mentioned in the sagas were murdered. Similarly high homicide rates, mainly due to cycles of revenge killing between feuding families, have been reported for some modern hunter-gatherer and village-based societies ( SN Online: 9/27/12 ). Lethal raids by competing groups may go back 10,000 years or more ( SN: 2/20/16, p. 9
Murder rates rise in the absence of central authorities that enforce social order, Dunbar proposes. “The real issue is not that there were so many murders among Icelandic Vikings, but that murders were carefully calculated based on knowing whether one had a sufficient family advantage to take the risk.”

That idea relates to mathematical formulas of fighting strength developed during World War I by British engineer Frederick Lanchester. One of Lanchester’s laws calculates that the fighting advantage of a larger group over a smaller group grows disproportionately as the disparity in the size of war parties increases. That rule also holds for family-size differences in small-scale societies, such as Icelandic Vikings, Dunbar’s group concludes.

Tests of the possibility that greater kin numbers encourage lethal attacks in preindustrial groups, such as the Vikings, are rare, says Oxford evolutionary biologist and political scientist Dominic Johnson, who did not participate in the new study. Johnson has reviewed evidence suggesting that humans, chimps and social hunters such as wolves have evolved ways to monitor group sizes and launch attacks when they can gang up on a few opponents.

Dunbar and his colleagues studied three Icelandic family sagas covering events from around 900 to 1100. Iceland’s first settlers arrived from Scandinavia and northern Europe in the late 800s (SN: 5/14/16, p. 13).

The sagas contained information about events, including feuds and murders, involving 1,020 individuals. For everyone mentioned, the researchers identified a network of biological and in-law relationships.

Under Norse law, a murder entitled a victim’s relatives to compensation, either via a revenge murder or blood money. Icelandic sagas describe the importance of avenging murdered relatives to save face and prevent further attacks, regardless of family size.

In the three sagas, a total of 66 individuals caused 153 deaths; two or more attackers sometimes participated in the same killing. No killers were biologically related to their victims (such as cousins or closer), but one victim was a sister-in-law of her killer.

About two-thirds or more of killers had more biological kin on both sides of their families, and more in-laws, than their victims did.

Six men accounted for about 45 percent of all murders, each killing between five and 19 people. Another 23 individuals killed two to four people. The rest killed once. Frequent killers had many more social relationships, through biological descent and marriage, than their victims did, suggesting that they targeted members of families in vulnerable situations, the researchers say.

Picture a learning curve. Most of us imagine a smooth upward slope that rises with steady mastery. It is the ultimate image of progress.
But that image, as behavioral sciences writer Bruce Bower reports in “Kids learning curve not so smooth” (SN: 11/26/16, p. 6), may well be an illusion of statistics, created when people look at averages of a group instead of how individuals actually learn. That’s what scientists at the University of Cambridge found when quizzing preschoolers’ developing ability to understand that other people can have false beliefs, an important milestone in the development of a theory of mind.
For many learners, the study suggests, mastery comes in fits and starts, a graphical zigzagging that denotes steps forward and back. Insight into a problem can be quick for some, but many people follow a more meandering path to knowledge and understanding.

I recognize the truth of this in my own life, be it learning about a new subject or (especially) a new skill. I see it in my 5-year-old daughter as she learns to read. If you are not struck by a single dramatic aha! you can still make it work by moving forward, then back, aiming for progress and mastery.

Scientific advances also do not always follow a smooth upward curve. As staff writer Meghan Rosen writes in “Dinosaurs may have used color as camouflage” (SN: 11/26/16, p. 24), paleontologists did have a fairly sudden insight into how to get clues about the colors that decorated dinosaur skin: Look for pigment-containing structures called melanosomes. But identifying these microscopic structures in well-preserved fossils of soft tissue, while distinguishing them from bacteria that might have feasted on the fresh dead dino skin, has been a bit of a zigzag. There’s an ongoing back-and-forth critique between those scientists who claim they’ve discovered melanosomes and those who question such claims. It may be a long time before we know whether we will be able to truly repaint dinosaurs’ colors accurately, or use that information to better understand their lifestyles or habitats (as many scientists working in the field hope). But current investigations are already taking us closer to that goal, even if via a meandering path.

The danger of looking at the average, as evidenced in Bower’s news story, is also at play in Amy McDermott’s story “Lichens are an early warning system for forest health” (SN: 11/26/16, p. 20). Lichens are very sensitive to air pollution, a quality exploited for decades to monitor the air quality of forests and alert forest managers to looming issues. But if you were to look at overall lichen abundance you might not see any problem. Air pollution tends to encourage some species while discouraging others — a subtlety that a lichen average growth rate might miss. With on-the-scene reporting in the Pacific Northwest, McDermott details the history of lichen use in environmental quality studies and the new effort to use lichens as an indicator of climate change in forests.

Looking at averages can tell you part of a story, but it rarely tells you the whole story. What you may miss is the rich variety found in the real world — be it in students or lichens or even scientific perspectives.

That past-its-prime bag of spinach buried in the back of your fridge should probably hit the compost heap instead of your dinner plate. The watery gunk that accumulates at the bottom of bagged salad mix is the perfect breeding ground for Salmonella bacteria that could make people sick, researchers report November 18 in Applied and Environmental Microbiology.

The culprit? The juice that oozes out of cut or damaged leaves. After five days in the fridge, small amounts of plant juice sped up Salmonella growth. The bacteria grew avidly on the bag and stuck persistently to the salad leaves, so much so that washing didn’t remove the microbes.

Salmonella’s success inside bagged salads means it’s important for producers to avoid bacterial contamination from the get-go — and for consumers to eat those greens before they get soggy. Popeye would approve.

Drug use continued to threaten the health and safety of the American public in 2016, while a hidden menace in drinking water remained a major worry for the people of Flint, Mich.

Teen vaping
Vaping has surpassed cigarette smoking among U.S. high school students, according to a report released in 2016 from the National Youth Tobacco Survey. Estimates suggest that some 2.39 million U.S. high school kids vaped in 2015, compared with an estimated 1.37 million who smoked cigarettes (SN: 5/28/16, p. 4). The popularity of e-cigarettes has increased recently despite a lack of evidence showing that they are safer than conventional tobacco products, according to the U.S. Food and Drug Administration, which in May extended its regulatory authority to e-cigarettes. Studies reported in 2016 show a host of potential health risks, including effects on the brain, immune system and fertility (SN: 3/5/16, p. 16).
Opioid epidemic
Against a backdrop of rising prescription opioid addiction, deaths related to opioid use have become an issue of national importance. A surge in fentanyl-spiked drugs emerged as a primary concern in 2016 (SN: 9/3/16, p. 14). U.S. deaths from synthetic opioids rose from 3,105 in 2013 to 5,544 in 2014, a change that could not be explained by fentanyl prescription rates, according to a report released in August by the Centers for Disease Control and Prevention. Drug enforcement seizures involving fentanyl more than doubled from 2014 to 2015.

Fallout in Flint
After lead in the drinking water in Flint, Mich., launched a public health crisis (SN: 3/19/16, p. 8), a federal state of emergency remained in effect into August. The most recent tests conducted by the U.S. Environmental Protection Agency show that levels of lead, which is toxic to the brain, are below those considered dangerous and that filtered tap water is safe to drink. Many residents are still relying on bottled water, however. There’s also growing concern that lead contamination and testing is not being taken seriously elsewhere in the United States.

The moon is made of moons, new simulations suggest. Instead of a single colossal collision forming Earth’s cosmic companion, researchers propose that a series of medium to large impacts created mini moons that eventually coalesced to form one giant moon.

This mini-moon amalgamation explains why the moon has an Earthlike chemical makeup, the researchers propose January 9 in Nature Geoscience.

“I think this is a real contender in with the other moon-forming scenarios,” says Robin Canup, a planetary scientist at the Southwest Research Institute in Boulder, Colo., who was not involved in the new work. “This out-of-the-box idea isn’t any less probable — and it might be more probable — than the other existing scenarios.”
A collision between Earth and a Mars-sized object called Theia around 4.5 billion years ago is the current leading candidate for how the moon formed. This impact would have been a glancing blow rather than a dead-on collision, with most of the resulting building materials for the moon coming from Theia. But the moon and Earth are compositional dead ringers for one another, casting doubts on a mostly extraterrestrial origin of lunar material and thus the single impact explanation.
Planetary scientist Raluca Rufu of the Weizmann Institute of Science in Rehovot, Israel, and colleagues dusted off a decades-old, largely disregarded hypothesis that the moon instead formed from multiple impacts. In this scenario, the early Earth was hit by a series of objects a hundredth to a tenth of Earth’s mass. Each impact could have created a disk of debris around Earth that assembled into a moonlet, the researchers’ simulations show. Over tens of millions of years, about 20 moonlets could have ultimately combined to form the moon.
Multiple impacts help explain why Earth and the moon are chemically similar. For example, each impact may have hit Earth at a different angle, excavating more earthly material into space than a singular impact would.

The single impact hypothesis has about a 1 to 2 percent chance of yielding the right lunar mix based on the makeup of potential impactors in the solar system. In the researchers’ simulations, the multiple impact scenario is correct tens of percent of the time. Further investigation of the interiors and composition of the Earth and moon, the researchers say, should reveal whether this explanation is correct.

Ancient North Americans hunted with spear points crafted to absorb shock.

Clovis people, who crossed a land bridge from Asia to North America around 13,500 years ago, fashioned stone weapons that slightly crumpled at the base rather than breaking at the tip when thrust into prey, say civil engineer Kaitlyn Thomas of Southern Methodist University in Dallas and colleagues. The Clovis crumple rested on a toolmaking technique called fluting, in which a thin groove was chipped off both sides of a stone point’s base, the researchers report in the May Journal of Archaeological Science.
Computer models and pressure testing of replicas of fluted and unfluted Clovis points support the idea that fluted bases worked like shock absorbers, preventing tip breakage, the scientists conclude. Slight compression and folding of stone at the base of fluted points after an impact did not cause enough damage to prevent the points from being reused, they say.

“Fluted Clovis points have a shock-absorbing property that increases their durability, which fit a population that needed reliable weapons on a new, unknown continent,” says archaeologist and study coauthor Metin Eren of Kent State University in Ohio. While Clovis people weren’t the first New World settlers (SN: 6/11/16, p. 8), they roamed throughout much of North America. Individuals traveled great distances to find food and move among seasonal camps, Eren says.

Computer models run by Thomas, Eren and colleagues indicated that unlike unfluted points, fluted points increasingly divert pressure away from the tip and toward the base as physical stress on the weapon grows. Computerized, 3-D versions of fluted Clovis points exposed to high-impact pressure crumpled at the base, leaving the tip intact. Unfluted replicas, however, frequently broke at the tip.
Comparable results emerged when the researchers tested 60 fluted and unfluted stone replicas of Clovis points in a viselike machine that applied precise pressures. Each replica was the same size and represented the average outline shape of 241 previously excavated Clovis points. Standardized replicas enabled researchers to focus solely on whether fluting affected how Clovis points react to physical stress.
Fluted Clovis points may have been attached to handles or long shafts in ways that also enhanced the resilience of a weapon’s business end, Eren says. But no such handles, or even materials used to bind Clovis points to handles, have been discovered.

The fluted points would have taken patience and experience to produce, says Eren, himself a crafter of the stone tools. Previous finds suggest that as many as one out of five Clovis points broke as fluted sections were prepared. If all goes well for an experienced toolmaker, it takes 40 to 50 minutes to produce a fluted Clovis point, he estimates.

Fluting techniques became increasingly elaborate until the practice was abandoned around 9,500 years ago. At that time, familiarity with North America’s landscapes and stone sources triggered a shift to making unfluted spear points designed to kill more effectively, but not necessarily to last, Eren suspects. Some of those stone points may have been intended to shatter on impact, creating shrapnel-like wounds, he says.

Searching for signs of crumpling and crushing on the bottoms of early and later fluted Clovis points could help researchers see if the tools always worked as shock absorbers, says archaeologist Ashley Smallwood of the University of West Georgia in Carrollton.

Researchers have previously proposed that fluting represented a stylistic twist with no practical impact, or that it was a way for toolmakers to advertise their skills and suitability as mates, or was part of prehunt rituals. The new results provide an intriguing practical explanation for the technique’s popularity that deserves further study, says archaeologist Daniel Amick of Loyola University Chicago. Aside from their durability, fluted points may have held symbolic meaning for Clovis people, he adds. For instance, if ancient Americans didn’t fully grasp how fluting strengthens stone points, they could have incorporated the technique into supernatural explanations for the success of hunts, Amick suggests.

Most of a volcano’s magma probably isn’t the oozing, red-hot molten goo often imagined.

Analyses of zircon crystals, spewed from a volcanic eruption in New Zealand, show that the crystals spent the vast majority of their time underground in solid, not liquid, magma, researchers report in the June 16 Science. The results suggest the magma melted shortly before the volcano erupted.

This finding helps confirm geologists’ emerging picture of magma reservoirs as mostly solid masses, says geologist John Pallister of the U.S. Geological Survey in Vancouver, Wash., who was not involved in the study. And it could help scientists more accurately forecast when volcanoes are poised to erupt.
Studying magma reservoirs directly is difficult because they’re buried kilometers underground. Heat and pressure would destroy any instruments sent down there. So Kari Cooper, a geochemist at the University of California, Davis, and her colleagues probed magma by scrutinizing seven zircon crystals from New Zealand’s Taupo Volcanic Zone. These crystals formed between a few thousand and a few hundred thousand years ago, when molten magma from deeper in Earth’s crust crept up to the Taupo reservoir, cooled and crystallized into zircon and other minerals. Some of these other minerals eventually melted back into liquid magma and carried the zircon up and out during an eruption 700 years ago.
By examining the distribution of lithium in the zircon crystals, the researchers discerned how long the zircon had existed at temperatures hot enough to melt its mineral neighbors — that is, how long the magma had stayed molten. Lithium, which the crystals would have picked up from surrounding magma, spreads through zircon faster when it’s hotter, Cooper explains.

The diffusion of lithium indicated that the crystals spent, at most, about 1,200 years exposed to a temperature range of 650° to 750° Celsius. At those temperatures, solid magma melts into a state that’s a little like a snow cone — mostly crystalline, with a bit of liquid seeping through. And for just 40 years, the crystals were exposed to temperatures above 750° — hot enough for magma to completely melt. Since the magma spent the overwhelming majority of its lifetime in the reservoir as a mostly solid mass, scientists surmise it melted briefly only before eruption.

“The other cool thing that we found is that most of the crystals are more than 50,000 years old,” Cooper says. In the last 50,000 years, this volcanic system underwent many eruptions before belching up the studied zircon crystals 700 years ago. The relatively short time these crystals experienced high heat suggests that they weren’t affected much by the magma in those previous eruptions. “Everything has to be much more compartmentalized down there than we originally thought,” Cooper says.

The study’s findings raise questions about how mostly solid magma melts and mobilizes before an eruption, says George Bergantz, an earth scientist at the University of Washington in Seattle who was not involved in the research. Cooper suspects that molten material from even deeper underground seeps up and melts solid magma. But, she says, “it’s still very much an open question.”