Readers ask about cat contraception, big G and more

Feline fecundity

One shot of an experimental gene therapy kept female cats kitten-free for at least two years, Erin Garcia de Jesús reported in “Gene therapy prevents cat pregnancy” (SN: 7/15/23 & 7/29/23, p. 10).

Reader Christie Borem asked why the researchers focused on female cats.

It only takes one “pesky” male cat to impregnate multiple females, says reproductive biologist David Pépin of Massachusetts General Hospital and Harvard Medical School. If male contraceptives alone were used, nearly every male cat would need to receive treatment to prevent pregnancies in females. But each female cat that receives contraception is one less female giving birth to litters, regardless of the male population, Pépin says. What’s more, surgical sterilization is a more invasive procedure for female cats than it is for males, which makes females an ideal target for quick and easy birth control, he says.

With that said, contraception for both male and female cats would be helpful for controlling populations of feral cats, Pépin says. Researchers are developing new birth control methods for male cats, but none have proved permanent.

Spinning out

The North Pole drifted about 1.6 meters toward the east coast of Greenland between 1993 and 2010. About 78 centimeters, or about 4.4 cm per year, of that shift was due to irrigation alone, Sid Perkins reported in “Irrigation nudges the North Pole” (SN: 7/15/23 & 7/29/23, p. 12).

Reader Hugh Black wondered if factors such as population growth and climate change also contribute to polar drift.

Any relatively permanent redistribution of mass would contribute to drift, but water probably has the biggest influence, says Clark Wilson, a geophysicist at the University of Texas at Austin.

Glacier and ice sheet melting, which has accelerated over the last several decades, contributed about 4.1 cm/yr to the North Pole’s drift during the study period, Wilson and colleagues estimated. The team hasn’t looked at the effect of population growth, but Wilson speculates that its contribution to polar drift would likely be smaller than that of water impounded in reservoirs behind dams, which the team estimated to be about 1.5 cm/yr during the study period.

What’s the big G?

Physicists have spent centuries trying to pin down the value of Newton’s gravitational constant, or “big G,” James R. Riordon reported in “What is big G?” (SN: 7/15/23 & 7/29/23, p. 28).

Labs around the world attempting to measure G, which reflects the strength of gravity between things with mass, have turned up values that disagree. Reader Richard Bisk wondered whether dark matter could be influencing the measurements.

“Scientists have been trying to detect dark matter on Earth for decades without much success. We are still in the dark,” says physicist Stephan Schlamminger of the National Institute of Standards and Technology in G­aithersburg, Md. Some efforts to detect dark matter have used torsion balances, a tool that experimentalists measuring G also use. Since dark matter has yet to be detected with those efforts, it’s relatively safe to assume that the mysterious stuff does not influence measurements of G in a significant way, Schlamminger says. Still, dismissing the idea completely “would be foolish because detecting dark matter with a G experiment could easily lead to a [Nobel Prize],” he says.