Why don't more animals have opposable thumbs?
From CrowdScience by BBC World Service
February 20, 2026 · 26 min
About this episode
The episode explores the evolution of opposable thumbs in humans and other species, featuring insights from experts and a demonstration of a robotic Third Thumb.
On a recent kayaking trip, CrowdScience listener Lanier sliced through his right thumb, putting it out of action for a while. This made life difficult, as he couldn’t button his shirt, tie his shoelaces or type efficiently on his smartphone. Missing the use of his thumb made him wonder: since opposable thumbs are so advantageous to those of us who have them, why didn’t they evolve in more species? Host Marnie Chesterton unpicks the evolution of our own unique thumbs with the help of paleoanthropologist Tracy Kivell, learning how our grip compares to that of other animals. We discover why mammals like horses and dogs have no use for thumbs, and why we humans don’t have opposable big toes. Meanwhile, at Taronga Zoo in Sydney, Australia, senior keepers Tarryn Williams Clow and Bec Russell-Cook introduce us to two different marsupials. Humphrey the koala has not one but two thumbs on each hand. Why did koalas develop this anatomical quirk when their closest living relative, the wombat, has spade-like digits? Dr Mark Eldridge from the Australian Museum shares his hypothesis. And what if we, too, had another thumb? Marnie tries on a robotic Third Thumb, built by designer Dani Clode…
People in this episode
Host: Marnie Chesterton
Guests: Tracy Kivell, Tarryn Williams Clow, Bec Russell-Cook, Mark Eldridge, Dani Clode
Topics covered
- evolution
- opposable thumbs
- animal anatomy
- marsupials
Keywords
- kayaking
- koalas
- wombats
- robotic thumb
- neuroscience
Mentioned in this episode
Products: Third Thumb
Places: Sydney, Australia
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