Are Humans the Only Species to Drive Others to Extinction? And More Questions From Our Readers
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Are humans the only species to drive another to extinction? Tom Ruppel | Dixon, California
Human activities are the most prominent cause of species extinction today, but not the only one. A recent study estimated that over half of contemporary extinctions in land vertebrates were caused, at least in part, by invasive species. The domestic cat is among the worst offenders; its cuteness belies how devastatingly effective it is at hunting birds and small mammals. The cat’s influence has been most severe on islands where native species evolved without predators and therefore have no defenses. One can assign humans some of the blame for introducing predators. However, the fossil record shows that species have been going extinct for far longer than humans have been around. Some extinctions were caused by changes in the physical environment, such as the asteroid impact that killed off the dinosaurs (except for birds). However, many other species have gone extinct when nothing dramatic seemed to be happening. Some of these surely were related to the effects of predators, parasites and competitors—though the fossil record generally doesn’t give us enough information to identify the cause of a species’ demise. —Gene Hunt, curator of paleobiology, National Museum of Natural History
Why did Grover Cleveland lose his first re-election bid but win again four years later? Sue Conviser | New York City
Cleveland actually won the popular vote three times in a row, something very few presidents in American history have done. But he lost the Electoral College in 1888 because of the big states of Pennsylvania and New York. The electorate at the time was pretty grumpy, and there were huge swings between the two parties from one election to the next. One factor was that American industry was growing. People were moving more than they ever had before, immigrating from other countries and relocating from farms to big cities. In 1888, Cleveland’s Republican opponent, Benjamin Harrison, thought higher tariffs would protect American industry, while Democrats supported free trade. Cleveland lost New York by just 14,000 votes. (He would have fared worse overall if the Democratic Party hadn’t been intimidating Black voters in the South.) Harrison burned out his mandate quickly, leaving people dissatisfied; when Cleveland ran again in 1892, the nation gave him another chance. —Jon Grinspan, curator of political and military history, National Museum of American History
Which time zone do astronauts use on the International Space Station? Bruce W. Dietch | Bradenton, Florida
Astronauts on the ISS orbit the Earth 16 times each day, which could really confuse their bodies’ rhythms. As you can imagine, they also have very busy agendas. For both of these reasons, having a set schedule is important to the work they do. The Apollo and space shuttle missions used two different time systems: local time in Houston, where mission control still resides, and Mission Elapsed Time, the time since liftoff of the spacecraft. But before the first ISS occupants arrived at the station in November 2000, the 15 member countries agreed that they would use Coordinated Universal Time—which is the same as Greenwich Mean Time. —Jennifer Levasseur, museum curator, National Air and Space Museum
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This article is a selection from the March 2025 issue of Smithsonian magazine