Why Do So Few Mammals Go Through Menopause? And More Questions From Our Readers

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Smithsonian magazine

April/May 2026

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Why do so few mammals go through menopause?

Menopause happens when the older females of a species remain physically capable of contributing to their group’s survival, even as their ovarian follicles become depleted. This is a rare occurrence among wild animals because natural selection favors continued reproduction—more offspring means more descendants in the gene pool. According to the dominant theory, menopause is believed to evolve only in species where the payoff from helping existing children and grandchildren exceeds the benefits of producing more offspring. These are species that have long life spans, extended periods of offspring dependency and stable multigenerational social groups where post-reproductive females can meaningfully increase their descendants’ survival. Menopause has been found in one population of chimpanzees and in one individual captive orangutan. Generally, though, only humans and certain toothed whales, particularly killer whales and short-finned pilot whales, meet the stringent requirements and have menopause throughout the species.—Janine Brown, research physiologist, National Zoo and Conservation Biology Institute

Before personal timekeeping was common, how did early Americans arrange meetings and keep appointments?

Although relatively few people in early America owned clocks and watches, they were able to rely on other sources to track time. Most of the population lived in rural areas, and the sun—not mechanical timepieces—ruled the day. Almanacs gave information about lunar and solar cycles, so people could keep track of planting seasons and market dates. In the military, soldiers got their signals through the sound of a bugle or a drum. In a city like Boston, people who lived within earshot of the Old North Church, for example, could mark the time by mechanical clocks that rang on the hour. Sundials were also surprisingly accurate; when people did begin owning clocks and watches, they used sundials to set them to the minute. In general, early Americans—­even businessmen in towns—didn’t schedule appointments to the minute or rush to beat the clock. They maintained a different pace of life.—Carlene Stephens, retired curator of work & industry, National Museum of American History

Are there any planets in space that don’t orbit around a star?

As planetary systems form, it’s theoretically possible that some planets whose orbits haven’t fully stabilized could be kicked out of their star systems through close gravitational encounters with other planets or stars. In stellar nurseries, where many new solar systems are forming, the James Webb Space Telescope has detected hundreds of isolated objects smaller than Jupiter. These might be planets, based on their small mass. However, they might be miniature brown dwarfs (failed stars that are too small to fuse hydrogen the way our sun does). Demonstrating that ejected “free-floating planets” exist and do not have host stars is part of the mission of the upcoming Nancy Grace Roman Space Telescope.—Jennifer C. Yee, observational astronomer, Center for Astrophysics, Harvard & Smithsonian