Readers ask about the limits of de-extinction, crater shapes and more

Mirror, mirror

Clay models of dull and shiny beetles showed that Christmas beetles’ mirrorlike exterior may not serve as a form of camouflage against predators, Susan Milius reported in “Scientists scuff a theory about shiny disguises” (SN: 4/9/22, p. 4).

Perhaps the clay models were simply not able to reproduce all the potential ways that the beetles’ glittery bodies affect light and protect the insect, reader Ron Kern suggested.

It’s true that the clay models didn’t mimic all possible light effects generated by Christmas beetles, Milius says. But that wasn’t the aim of the experiment. Think of the study as a sort of dissection, examining just one possible light trick at a time, she says. The results suggest that shine by itself isn’t a deterrent against predators. Further testing could investigate whether other aspects of the beetle’s mirror surface might offer benefits to these showy insects, Milius says.

Crater shapes

The impact that forged Hiawatha crater in Greenland happened about 58 million years ago, Carolyn Gramling reported in “Greenland impact crater is surprisingly old” (SN: 4/9/22, p. 5).

Reader Barry Maletzky asked why most impact craters are circular given that space rocks can strike at different angles.

Most craters are circular because of an impactor’s explosive punch, says associate news editor Christopher Crockett. When space rocks crash into rocky planets and moons at high velocity, a tremendous amount of energy is transferred within a short period of time. At most angles of impact, such a process produces the typically round craters we see, scientists reported in 2013 in the Journal of Geophysical Research: Planets. “The effect is similar to planting explosives at the site and letting them blow,” Crockett says.

Although they’re rare, elliptical craters do occur in the solar system, and impact angle plays a role. The angle at which a crater becomes more likely to be elliptical than round depends on space rock size, impact velocity and type of material at the impact site, the study showed.

Resurrection roadblock

Scientists re-created the genome of the extinct Christmas Island rat by comparing it against the genome of a living relative. But some key DNA remains a mystery, Anna Gibbs reported in “Rat reveals limits of de-extinction” (SN: 4/9/22, p. 12).

Reader Tim Cliffe wondered if a complete genome could be reconstructed given enough DNA samples from different specimens of the extinct species.

The issue isn’t that DNA is missing, but that scientists can’t make sense of all the genetic sequences they have, says Tom Gilbert, an evolutionary biologist at the University of Copenhagen. Some genes in the Christmas Island rat’s genome have diverged so much that they aren’t remotely similar to the reference genome. If we can’t identify the gene, we are unable to re-create it in a reference genome for the purpose of de-extinction, Gilbert says.

Deciphering brain waves

Researchers are studying the emotions of horses, octopuses and other creatures to understand how animals experience the world, Alla Katsnelson reported in “What do animals feel?” (SN: 4/9/22, p. 16).

In one study, horses that spent more time alone had more gamma brain wave a­ctivity than horses that grazed freely with a herd, Katsnelson reported. In people, high levels of such brain wave activity have been linked to anxiety and stress. Reader Barbara Allan thought that it was the opposite: Low levels of gamma brain wave activity are linked to stress and anxiety in humans.

Scientists are still working out how brain waves in people relate to various mental states, Katsnelson says. Studying brain waves and interpreting those studies is complicated, and the findings in this field vary. In their report, the researchers who studied horses point to evidence linking anxiety and stress to more gamma waves in people, she says. But other groups have found conflicting results, complicating the picture.