Where Do We Get Seeds for Seedless Fruit? And More Questions From Our Readers

Where do we get the seeds for seedless fruit? Dan Holden | Essexville, Michigan

You don’t need seeds to grow seedless fruit. In one method, you take vegetative cuttings of the parent plant and root them out, essentially cloning it. Another is grafting, or taking a branch of the parent plant and joining it to a different plant. But most seedless bananas and watermelon are grown from triploid plants. Those are plants that have three sets of chromosomes (either through natural mutation or through breeding), and this keeps the plants from pairing chromosomes to reproduce. This makes them sterile, and the fruits they produce lack seeds. When a sterile plant develops fruit, it’s called parthenocarpy, which is Greek for “virgin fruit.” —Joe Brunetti, lead horticulturist, Smithsonian Environmental Research Center

How can we tell from fossil records whether a dinosaur was omnivorous? Phillip Flach | Belleville, Illinois

It’s hard to know for sure what any dinosaur species ate. Only a handful of dinosaurs have been found with direct evidence of their diet. In 2020, for instance, an armored Borealopelta was discovered with fern leaves and other plant matter still in its stomach. But a discovery like this is very rare. (And even then, it only reveals a single meal.) As paleontologists, we generally rely on physical features like tooth shape and jaw structure to infer what a dinosaur ate. These features can help us pinpoint whether a species was carnivorous or herbivorous—and most dinosaurs seem to have been primarily meat- or plant-eaters. But some species of dinosaur had beaks instead of teeth, which could have been used to eat meat, or plants, or both. (These include dinosaur families called ornithomimids, oviraptorids and caenagnathids.) Dinosaurs probably changed their diet as they evolved and perhaps ate different kinds of food at different times of the year, but it’s hard to know the specifics from the fossils we have. —Matthew Carrano, paleontologist, National Museum of Natural History

How did the moon end up spinning on its axis at exactly the same speed as it rotates around the Earth, so that we always just see one side of it? David Asplin | Spokane, Washington

The short answer is that gravity is responsible. The moon was born about 4.5 billion years ago out of the debris from a giant collision between the Earth and an object about the size of Mars. We know about this fantastic cataclysm from analyses of lunar rock samples. (Six of the Apollo missions, from 1969 to 1972, brought back a total of 842 pounds of rocks, dust and core samples from the moon.) The moon has been slowly drifting away from the Earth since its birth. The two bodies exert gravitational pulls on each other, as we know from our ocean tides, and that pull was even stronger when the moon and Earth were closer together. Over the long course of cosmic time the gravitational interaction between the Earth and the moon brought the moon into “synchronous rotation,” meaning that the moon’s rate of spin on its axis (its rotation) became the same as the rate it orbited the Earth. Gravity still keeps the moon locked in its synchronous rotation pattern. And the moon is still moving away from us—currently at a rate of about two inches per year. —Howard A. Smith, senior astrophysicist, Center for Astrophysics | Harvard & Smithsonian