One day last November, my dog, Forrest, sat on the cold marble steps of the Smithsonian's natural-history museum in Washington, D.C., ready to meet Celine Halioua, a woman who may one day add a tail-wagging year or so to his life, and also the lives of millions of other dogs. In 2019, Halioua founded a company called Loyal, and in February 2025, a pill that she developed for dogs was deemed likely to be effective by the FDA. If the company ticks a few remaining boxes, the drug could soon be on sale, kick-starting a new era of longevity medicine that could eventually also lengthen humans' lives. More than 10,000 years ago, dogs made a farseeing bet on humans. They padded carefully up to our campfires, ate scraps, and kept watch, hitching their fates to a species that would soon bestride the planet. They have since become the fourth-most-populous large land mammal, trailing only sheep, cows, and goats, which all lead less pampered lives. Now we're trying to keep our best animal...
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