What if you had no thumbs?

Wiggle your thumb. Now touch your thumb to each finger, one by one.

Your thumb helps you hold things. What if you had no thumbs at all?

Try this: touch the tip of your thumb to the tip of your pointer finger, then your middle finger, ring finger and little finger. Easy, right? Now pick up a pencil, a coin or a cup and notice what your thumb is doing.

Your thumb is part of almost everything your hands do. So what if you had no thumbs? We can't take away anyone's thumbs, but we can follow the clues: how thumbs grip, how they help with tools, and how other animals manage.

Human hands perform an enormous range of tasks, and the thumb takes part in most of them. Anatomists name its signature movement opposition.

This thought experiment removes the thumbs and asks what changes. It follows three threads: how the thumb moves and grips, what thumbs mean for using tools, and how two other mammals, chimpanzees and giant pandas, solve grasping problems with their own hands. Anatomy and animal behavior come from sources; the consequences for a thumbless person are reasoned ideas.

Your thumb sits apart from your fingers. It can swing across your hand.

That lets it meet each fingertip. It is like a helper that pinches and holds.

Your thumb isn't lined up with your fingers. It sits off to the side, joined to your wrist by a special joint shaped a bit like a horse saddle. That joint lets the thumb swing in many directions.

The OpenStax anatomy textbook names the move where the tip of your thumb touches the tip of a finger: opposition. Moving the thumb back beside your pointer finger is called reposition. Thanks to opposition, you can pinch a tiny bead, hold a pencil or grip a cup handle.

OpenStax defines opposition as the thumb movement that brings the tip of the thumb into contact with the tip of a finger, produced at the first carpometacarpal joint: a saddle joint between the trapezium carpal bone and the first metacarpal. Opposition combines flexion and abduction of the thumb at this joint; returning the thumb beside the index finger is reposition.

The thumb's other movements happen at the same joint. Abduction swings it forward to point straight out from the palm, at 90 degrees; flexion brings it across the palm or against the index finger.

Now pretend you have no thumbs. Try to pick up a crayon with just your fingers.

It is tricky! Buttons, spoons and zippers might be hard too.

Without thumbs, there would be nothing to press against your fingers. You could still scoop things up or hook them with your fingers, and you could hold things between two hands. But pinching a small object, writing with a pencil or turning a key might be much harder.

People are inventive, though. Without thumbs, we might design chunkier handles, use both hands for jobs that need one today, or invent new tools. These are our ideas about a thumbless world, not things anyone has tested.

Without opposition, the hand loses the ability to bring a digit pad-to-pad with the others, so pinch and precision grips between thumb and finger would be gone. Hook-like grasps with the fingers alone, and two-handed holds, would remain.

It is reasonable to expect that fine manipulation, writing, fastening and the operation of tools sized for opposable thumbs would become difficult, and that tools and habits would change in response. How far human tool use would have developed without thumbs is a much larger question that this lab cannot answer; it stays an idea.

Chimpanzees have thumbs like ours. They use them to hold branches and food.

Chimps even make tools! They poke sticks into termite nests to catch a snack.

We're not the only animals with opposable thumbs. The San Diego Zoo says chimpanzees have them too, and use them to grasp branches and grab a bite to eat.

Chimps are also famous tool users. They strip the leaves off a twig and dip it into an ant or termite nest to fish out the insects. When water is hard to find, they chew leaves into a soft sponge to soak up rainwater from holes in trees. Britannica adds that young chimps learn these skills from older ones.

Chimpanzees share opposable thumbs with us, which they use to grasp branches and food (San Diego Zoo Wildlife Alliance). They strip twigs to probe ant and termite nests and chew leaves into sponges to collect rainwater from tree holes.

Britannica notes that chimpanzees use tools for foraging, cracking nuts and hygiene, with younger individuals learning these behaviors from their elders, a form of culture. Chimps also walk on their knuckles, so their hands serve for travel as well as for handling things.

A giant panda has a bump on its paw that works like a thumb.

It is really a big wrist bone! The panda uses it to hold bamboo.

Giant pandas spend 10 to 16 hours a day finding and eating bamboo, the Smithsonian's National Zoo says, usually sitting upright like a person on the floor. To hold the stems, they use something special: a 'pseudo thumb.' Pseudo means pretend.

The Smithsonian's National Zoo explains that the panda's pseudo thumb is really a long, enlarged wrist bone covered with a fleshy pad. It isn't a true thumb, but it works with the paw to grasp bamboo. So when an animal really needs to grip, nature can find more than one way to make a 'thumb.'

The Smithsonian's National Zoo and Conservation Biology Institute describes how a giant panda usually eats sitting upright, leaving its front paws free to grasp bamboo with a 'pseudo thumb' formed by an elongated, enlarged wrist bone covered by a fleshy pad. Its powerful jaws and teeth then crush the fibrous stems.

The pseudo thumb is not a digit: it does not have the human thumb's saddle joint or opposition. It is a separate solution to the same problem of gripping, which is a reminder that a thumbless human might likewise find workarounds, though only an idea can say which.