Readers weigh in on mathematical animals and more

Critter calculations

Savvy for judging quantities is turning up across the animal kingdom — even among spiders and other invertebrates, Susan Milius reported in “Animal math” (SN: 12/10/16, p. 22).

Some astute readers pointed out that designing experiments to test animals’ quantitative skills takes great ingenuity, but sometimes human bias may skew the results.

“Articles on animal cognition often presuppose that animals are non-intelligent. Thus, when researchers find that a dog can distinguish between a small and large number of items, it’s hailed as significant,” Matthew Fisher wrote. “If we think of cognition as existing along an evolutionary continuum, then results such as these are not surprising. The same evolutionary forces shape human cognition as in any other animal,” he wrote. “We need to move away from the unscientific, C­artesian notion that animals are unthinking automata.”

Irene Pepperberg, who studies the language and number-related abilities of African gray parrots and other birds at Harvard University, objected to Milius’ suggestion that no one seriously argues that nonhuman animals possess symbolic numerical systems. “Several respected scientists, myself included, argue exactly that,” Pepperberg wrote.

“I certainly didn’t intend to dismiss this work,” Milius says. “I was trying to conjure up the simplistic Dr. Dolittle case of nonhuman animals having a whole symbolic system parallel to humans’ — woof for 1, double-woof for 2, for example — that scientists have only to decode.”

Raise a glass

Science writer Dava Sobel’s book The Glass Universe tells the story of women “computers” at Harvard Observatory. Beginning in the late 1800s, these women charted the heavens using glass photographic plates, Macon Morehouse, Science News’ Deputy Managing Editor, News, wrote in her review “Astronomy’s unsung heroines get their due” (SN: 12/10/16, p. 28).

Online reader Jan Steinman asked how black and white lines on the plates provide hints to a star’s elemental makeup.

Prisms inside telescopes split light from a star into a spectrum, which appears as a black streak on a plate. Within this streak are patterns of spectral lines — the result of a star’s elements or molecules emitting and absorbing photons of light at distinct wavelengths. “It’s kind of like taking a black-and-white picture of a rainbow,” says astronomy writer Christopher Crockett. “The color information is still there, just spread out across the image.” Spectral lines can also tell astronomers about a star’s temperature and velocity, for example, and are used to study other celestial bodies including galaxies, asteroids and comets.

Belly of the beast

Plant-eating mammals have bigger torsos relative to body size than carnivores, but the same might not have held true for dinosaurs, Emily DeMarco reported in “Boning up on belly size” (SN: 12/10/16, p. 32).

Online reader Stanton de Riel wondered if dinosaurs, like their modern avian descendants, had gizzards that may have helped with digestion.

“Yes, there were some dinosaurs that used a gizzard with grinding stones,” says Marcus Clauss, a physiologist at the University of Zurich. Some dinosaurs even evolved grinding teeth along with gizzards — a “seeming aberration” because there is no known advantage to having both, Clauss says. It’s possible the creatures ate particularly tough plant food. None of those dinosaurs were included in the recent analysis.

Correction

“Mount St. Helens is a cold-hearted volcano” (SN: 12/10/16, p. 4) states that the volcano’s magma source originates from the Juan de Fuca plate melting as it descends beneath the North American plate. This is incorrect. As the Juan de Fuca plate descends, it releases fluids that rise and trigger melting in the rock above.