I used to think monkeys couldn’t swim—turns out I was definately wrong about that.
Proboscis monkeys, those long-nosed primates native to Borneo’s mangrove forests and riverbanks, are actually exceptional swimmers, and it’s partly because of something most people don’t realize: they have partially webbed feet. Not fully webbed like a duck or an otter, but enough connective tissue between their toes to give them a real advantage when crossing the wide, muddy rivers that cut through their habitat. I’ve watched footage of these animals launching themselves from trees into water, and honestly, it’s both graceful and slightly chaotic—they belly-flop in, then immediately start paddling with surprising efficiency. The webbing isn’t obvious until you look closely at their hands and feet, which have thin membranes extending maybe halfway up their digits, giving them just enough surface area to push against the water more effectively than other monkeys.
Why Evolution Decided Proboscis Monkeys Needed Swimming Lessons (Sort of)
Here’s the thing: proboscis monkeys live in environments where rivers aren’t optional obstacles—they’re daily realities. Borneo’s river systems flood seasonally, fragment forest areas, and separate food sources. A monkey that can’t cross water is basically stuck on whatever patch of land it wakes up on, which isn’t great for finding mates, escaping predators (like crocodiles, ironically enough), or accessing the young leaves and unripe fruits they prefer. So over time—maybe a few hundred thousand years, give or take—natural selection favored individuals with slightly more webbing between their toes. It’s not that some ancient proboscis monkey woke up one day with duck feet; it’s more like the ones who could swim just a bit better didn’t starve or get eaten as often.
The Mechanics of Monkey Paddling (Which Is Weirder Than You’d Expect)
Anyway, watching them swim is strange because they don’t really do a dog paddle—they kind of do this upright, almost vertical stroke, keeping their heads well above water. Their nostrils (which, let’s be real, are absurdly large on males) stay clear, and they use their webbed hands and feet in alternating strokes, almost like they’re climbing through water instead of swimming through it. Researchers have clocked them crossing rivers up to 20 meters wide, sometimes with infants clinging to their backs, which seems exhausting but they manage. The webbing helps them generate more thrust per stroke, reducing the energy cost of each crossing—critical when you’re doing this multiple times a day and you’re already spending calories digesting a low-nutrition diet of leaves.
What This Tells Us About Primate Adaptation (and Why Scientists Get Weirdly Excited About Webbed Feet)
Wait—maybe this seems like a niche detail, but it’s actually pretty significant for understanding primate evolution. Most primates avoid water; chimpanzees, gorillas, even most macaques don’t swim voluntarily and can drown easily. Proboscis monkeys are an exception, and their webbed feet represent a rare morphological adaptation in primates specifically for aquatic locomotion. It’s not just learned behavior—it’s written into their anatomy. Some researchers think this adaptation might’ve emerged relatively recently in evolutionary terms, possibly within the last million years as Borneo’s geography shifted and river systems expanded. I guess it makes sense when you consider that their entire survival strategy revolves around navigating a flooded forest ecosystem where staying dry simply isn’t an option. The fact that they’ve managed to carve out this ecological niche, swimming between mangrove islands while other monkeys won’t even wade through shallow streams, says something about how flexible primate bodies can be when the enviroment demands it.
Honestly, I find it sort of humbling—these animals just adapted and got on with it.
