Turns out we may be unfairly stereotyping dogs.

Modern breeds are shaped around aesthetics: Chihuahuas’ batlike ears, poodles’ curly fur, dachshunds’ hot dog shape. But breeds are frequently associated with certain behaviors, too. For instance, the American Kennel Club describes border collies as “affectionate, smart, energetic” and beagles as “friendly, curious, merry.”

Now, genetic information from more than 2,000 dogs, paired with self-reported surveys from dog owners, indicates that a dog’s breed is a poor predictor of its behavior. On average, breed explains only 9 percent of the behavioral differences between individual dogs, researchers report April 28 in Science.
“Everybody was assuming that breed was predictive of behavior in dogs,” geneticist Elinor Karlsson of the University of Massachusetts Chan Medical School in Worcester said in an April 26 news briefing. But “that had never really been asked particularly well.”

Geneticists had asked the question before in different ways. One study in 2019 looked at whether genetics might explain collective variation between breeds and found that genes could explain some of the differences between, say, poodles and chihuahuas (SN: 10/1/19). But Karlsson and her colleagues wanted to learn how much breed can predict variation in individual dogs’ behavior.

To study variation at the individual level, the team needed genetic and behavior data from a lot of dogs. So they developed Darwin’s Ark, an open-source database where more than 18,000 pet owners responded to surveys about their dog’s traits and behavior. The survey asked over 100 questions about observable behaviors, which the researchers grouped into eight “behavioral factors,” including human sociability (how comfortable a dog is around humans) and biddability (how responsive it is to commands).

The researchers also collected genetic data from 2,155 purebred and mixed-breed dogs, including 1,715 dogs from Darwin’s Ark whose owners sent in dog saliva swabs. The inclusion of mixed-breed dogs, or mutts, shed light on how ancestry affects behavior while removing the purebred stereotypes that could affect the way the dog is treated — and thus behaves.

Studying mutts also makes it easier to decouple traits from one another, says Kathleen Morrill, a geneticist in Karlsson’s lab. “And that means on an individual basis, you’re going to have a better shot at mapping a gene that is actually tied to the question you’re asking.”

Then the team combined the genetic and survey data for the individual dogs to identify genes associated with particular traits. The new study revealed that the most heritable behavioral factor for dogs is human sociability, and that motor patterns — such as howling and retrieving — are generally more heritable than other behaviors.

That makes sense, Kathryn Lord, an evolutionary canine biologist in Karlsson’s lab, said during the briefing. Before modern breeding started within the last couple hundred years or so, dogs were selected for the functional roles they could provide, such as hunting or herding (SN: 4/26/17). Today, these selections still show up in breed groups. For instance, herding dogs on average tend to be more biddable and interested in toys. It also follows that, within breed groups, individual breeds are more likely to display certain motor patterns: Retrievers, unsurprisingly, are more likely to retrieve.

Still, even though breed was associated with certain behaviors, it was not a reliable predictor of individual behavior. While retrievers are less likely to howl, some owners reported that their retrievers howled often; greyhounds rarely bury toys, except some do.

The research solidifies what people have observed: Dog breeds differ on average in behavior, but there’s a lot of variation within breeds, says Adam Boyko, a canine geneticist at Cornell University who was not involved in the study.

Surprisingly, size had even less of an effect — as in, virtually none — on an individual’s behavior, despite the yappiness commonly associated with small dogs. Boyko points out that small dogs may often behave worse than large dogs, but rather than that being built into their genetics, “I think it’s that we typically tolerate poor behavior more in small dogs than we do in big dogs.”

As a dog trainer, Curtis Kelley of Pet Parent Allies in Philadelphia says that he meets a dog where it’s at. “Dogs are as individual as people are,” he says. Breed gives a loose guideline for what kind of behaviors to expect, “but it’s certainly not a hard-and-fast rule.”

If a person is looking to buy a dog, he says, they shouldn’t put too much stock in the dog’s breed. Even within a litter, dogs can show very different personalities. “A puppy will show you who they are at eight weeks old,” Kelley says. “It’s just our job to believe them.”

More of the ingredients for life have been found in meteorites.

Space rocks that fell to Earth within the last century contain the five bases that store information in DNA and RNA, scientists report April 26 in Nature Communications.

These “nucleobases” — adenine, guanine, cytosine, thymine and uracil — combine with sugars and phosphates to make up the genetic code of all life on Earth. Whether these basic ingredients for life first came from space or instead formed in a warm soup of earthly chemistry is still not known (SN: 9/24/20). But the discovery adds to evidence that suggests life’s precursors originally came from space, the researchers say.
Scientists have detected bits of adenine, guanine and other organic compounds in meteorites since the 1960s (SN: 8/10/11, SN: 12/4/20). Researchers have also seen hints of uracil, but cytosine and thymine remained elusive, until now.

“We’ve completed the set of all the bases found in DNA and RNA and life on Earth, and they’re present in meteorites,” says astrochemist Daniel Glavin of NASA’s Goddard Space Flight Center in Greenbelt, Md.

A few years ago, geochemist Yasuhiro Oba of Hokkaido University in Sapporo, Japan, and colleagues came up with a technique to gently extract and separate different chemical compounds in liquified meteorite dust and then analyze them.

“Our detection method has orders of magnitude higher sensitivity than that applied in previous studies,” Oba says. Three years ago, the researchers used this same technique to discover ribose, a sugar needed for life, in three meteorites (SN: 11/22/19).

In the new study, Oba and colleagues combined forces with astrochemists at NASA to analyze one of those three meteorite samples and three additional ones, looking for another type of crucial ingredient for life: nucleobases.

The researchers think their milder extraction technique, which uses cold water instead of the usual acid, keeps the compounds intact. “We’re finding this extraction approach is very amenable for these fragile nucleobases,” Glavin says. “It’s more like a cold brew, rather than making hot tea.”

With this technique, Glavin, Oba and their colleagues measured the abundances of the bases and other compounds related to life in four samples from meteorites that fell decades ago in Australia, Kentucky and British Columbia. In all four, the team detected and measured adenine, guanine, cytosine, uracil, thymine, several compounds related to those bases and a few amino acids.

Using the same technique, the team also measured chemical abundances within soil collected from the Australia site and then compared the measured meteorite values with that of the soil. For some detected compounds, the meteorite values were greater than the surrounding soil, which suggests that the compounds came to Earth in these rocks.

But for other detected compounds, including cytosine and uracil, the soil abundances are as much as 20 times as high as in the meteorites. That could point to earthly contamination, says cosmochemist Michael Callahan of Boise State University in Idaho.

“I think [the researchers] positively identified these compounds,” Callahan says. But “they didn’t present enough compelling data to convince me that they’re truly extraterrestrial.” Callahan previously worked at NASA and collaborated with Glavin and others to measure organic materials in meteorites.

But Glavin and his colleagues point to a few specific detected chemicals to support the hypothesis of an interplanetary origin. In the new analysis, the researchers measured more than a dozen other life-related compounds, including isomers of the nucleobases, Glavin says. Isomers have the same chemical formulas as their associated bases, but their ingredients are organized differently. The team found some of those isomers in the meteorites but not in the soil. “If there had been contamination from the soil, we should have seen those isomers in the soil as well. And we didn’t,” he says.

Going directly to the source of such meteorites — pristine asteroids — could clear up the matter. Oba and colleagues are already using their extraction technique on pieces from the surface of the asteroid Ryugu, which Japan’s Hayabusa2 mission brought to Earth in late 2020 (SN: 12/7/20). NASA’s OSIRIS-REx mission is expected to return in September 2023 with similar samples from the asteroid Bennu (SN: 1/15/19).

“We’re really excited about what stories those materials have to tell,” Glavin says.

Leonardo da Vinci was wrong about trees.

The multitalented, Renaissance genius wrote down his “rule of trees” over 500 years ago. It described the way he thought that trees branch. Though it was a brilliant insight that helped him to draw realistic landscapes, Leonardo’s rule breaks down for many types of trees. Now, a new branching rule — dubbed “Leonardo-like” — works for virtually any leafy tree, researchers report in a paper accepted April 13 in Physical Review E.

“The older Leonardo rule describes the thickness of the branches, while the length of the branch was not taken into account,” says physicist Sergey Grigoriev of the Petersburg Nuclear Physics Institute in Gatchina, Russia. “Therefore, the description using the older rule is not complete.”
Leonardo’s rule says that the thickness of a limb before it branches into smaller ones is the same as the combined thickness of the limbs sprouting from it (SN: 6/1/11). But according to Grigoriev and his colleagues, it’s the surface area that stays the same.

Using surface area as a guide, the new rule incorporates limb widths and lengths, and predicts that long branches end up being thinner than short ones. Unlike Leonardo’s guess, the updated rule works for slender birches as well as it does for sturdy oaks, the team reports.

The connection between the surface area of branches and overall tree structure shows that it’s the living, outer layers that guide tree structure, the researchers say. “The life of a tree flows according to the laws of conservation of area in two-dimensional space,” the authors write in their study, “as if the tree were a two-dimensional object.” In other words, it’s as if just two dimensions — the width of each limb and the distance between branchings on a limb — determine any tree’s structure. As a result, when trees are rendered in two dimensions in a painting or on a screen, the new rule describes them particularly well.
The new Leonardo-like rule is an improvement, says Katherine McCulloh, a botanist at the University of Wisconsin–Madison who was not involved with this study. But she has her doubts about the Russian group’s rationale for it. In most trees, she says, the living portion extends much deeper than the thin surface layer.

“It’s really species-dependent, and even age-dependent,” McCulloh says. “A giant, old oak tree might have a centimeter of living wood … [but] there are certainly tropical tree species that have very deep sapwood and may have living wood for most of their cross sections.”

Still, the fact that the Leonardo-like rule appears to hold for many trees intrigues McCulloh. “To me, it drives home the question of why are [trees] conserving this geometry for their external tissue, and how is that related to the microscopic level differences that we observe in wood,” she says. “It’s a really interesting question.”

To test their rule, Grigoriev and colleagues took photographs of trees from a variety of species and analyzed the branches to confirm that the real-world patterns matched the predictions. The photos offer “a direct measurement of the characteristics of a tree without touching it, which can be important when dealing with a living object,” Grigoriev says.

Though the team hasn’t studied evergreens yet, the rule holds for all of the deciduous trees that the researchers have looked at. “We have applied our methodology to maple, linden, apple,” Grigoriev says, in addition to oak, birch and chestnut. “They show the same general structure and obey the Leonardo-like rule.”

While it’s possible to confirm the rule by measuring branches by hand, it would require climbing into trees and checking all the limbs — a risky exercise for trees and scientists alike. “Note,” the researchers write, “that not a single tree was harmed during these experiments.”