Contrary to popular belief, humans are not the only creatures with opposable thumbs. Rather, it is as if we are in an exclusive club with the few other animals that have this rare trait. Driving, eating, gaming, and much more – you use your thumbs every day, but you may be wondering: what exactly is an opposable thumb? How does it differ from other digits? And what makes it so special?
1. Humans
Little son helping his father with building work. Humans not only have opposable thumbs, but we can use our thumbs and hands in ways that animals cannot.
As humans, we rely heavily on our opposable thumbs for many activities of daily life. Try this – take a few minutes and try to do simple tasks without using your thumb. Fold it across your hand to keep it out of the way. Is it difficult to brush your teeth? Hold a fork? Open a door? Use a video game controller?
Humans not only have opposable thumbs, but we can use our thumbs and hands in ways that animals cannot. Bring your thumb across your palm to touch the base of your ring finger and pinky finger. Then, use the tip of each of these fingers to touch the base of your thumb. Animals with opposable thumbs can’t do this. Humans have increased dexterity that allows us to manipulate tools easily.
We may not be the only mammals with opposable thumbs, but we have a host of other characteristics that make us unique in the natural world. For example, we have unusually large brains for our size, and we can think in abstract terms like time and spirituality. We have a descended voice box and a bone below our tongue that is not attached to any other bones – together. These allow us to articulate words. We walk on two legs as a matter of course. And we make up for our lack of hair by wearing clothes. Humans are pretty strange animals!
2. Apes
A baby orangutan hangs in a tree in Borneo. Orangutans use their thumbs to climb trees, grasp branches, and hold tools.
The great apes, including the gorilla, chimpanzee, bonobo, orangutan, and lesser apes called gibbons, all have opposable thumbs. In fact, they take opposable digits a step further – the big toe of the foot is opposable as well!
Humans and apes share 97 percent similarities in DNA. We each have the genetic information that codes for a hand with four fingers and an opposable thumb. But how do the apes use their opposable thumbs?
They use their thumbs to climb trees, grasp branches, and hold tools – for example, using a small stick to gather ants or termites from a nest. Some apes may build shelters of leaves to get out of the rain. They groom one another, pinching pesky insects between the thumb and forefinger. They also use their thumbs in gathering food, such as picking fruit or peeling a banana – a task that would be nearly impossible without an opposable thumb.
3. Old World Monkeys
The Celebes crested macaque on the branch of the tree. They use their opposable thumbs for grasping tree branches.
Old World monkeys are those species native to Asia and Africa, as opposed to the New World monkeys of the Americas. There are twenty-three Old World monkey species, and most, including grivets, baboons, and macaques, use their opposable thumbs for grasping tree branches and other objects.
Not all Old World monkeys have opposable thumbs, though. In fact, the colobus monkey has no thumbs at all!
4. Lemurs
The ring-tailed lemur (Lemur catta) sitting in a tree. Like other primates, they use their thumbs for grasping branches and manipulating food.
Lemurs are primates found only on the island of Madagascar and a few other islands off the coast of Africa. The smallest of the 100 or so lemur species is only 3 inches in length, while others are several feet tall. Some researchers refer to the lemurs’ thumbs as “pseudo-opposable thumbs,” meaning that they are almost opposable but not quite. Like other primates, they use their thumbs for grasping branches and manipulating food. Other primates in the lemur family – pottos and lorises – also have pseudo-opposable thumbs.
5. Chameleons
A beautiful chameleon on a branch. The toes on their feet are arranged so that it makes it easier to grasp branches.
Chameleons use the special thumblike arrangement of the toes on their feet to grasp twigs and branches as they climb. Three toes make up the “medial bundle,” extending from the middle section of the foot. Two toes make up the “lateral bundle,” extending to the side. On the rear feet, this arrangement is reversed, with two toes in the medial position and three extending to the side.
6. Koalas
Koala, Phascolarctos cinereus, a mother with young standing on a branch. Koalas have an opposable toe on each foot.
The koala, the famed marsupial of Australia, is unlike any other animal in that it actually has two opposable thumbs. These thumbs are set at an angle to the three fingers. The koala uses these two sections of its hand – the thumbs and fingers – to securely grasp and climb tree branches.
Koalas also have an opposable toe on each foot. That earns them the world record of having six opposable digits!
7. Giant Pandas
A panda eats a large bamboo stalk. Giant pandas have a false thumb made up of an enlarged carpal bone.
Giant pandas (Ailuropoda melanoleuca) have an opposable thumb that has been called a false thumb. Rather than consisting of the distal and proximal phalange bones, the panda’s false thumb is an enlarged carpal bone – one of the many bones that together form the wrist. The false thumb functions as an opposable thumb opposite the five fingers, though, allowing the panda to grasp bamboo shoots and bring them efficiently to its mouth.
A fun fact about this feature is that it is commonly found in carnivores – whose dietary habits this giant furball tends to dabble in, if only on rare occasions.
What other bamboo-munching creature shares this rather interesting anatomical feature? The adorable red panda (Ailurus fulgens) – has no zoological relation to this large ursine. (Red pandas are actually considered cousins to weasels and raccoons.)
8. Possums and Opossums
The common brushtail possum is native to Australia, and the second largest of the possums. Spotted at Botanical Garden, Sydney, Australia.
Virginia opossums have a number of unique features. They are the only marsupial in North America, carrying young in a pouch like a kangaroo. They have grasping prehensile tails and opposable thumbs (actually, it is the fifth toe) on their hind feet. Together, the tails and thumbs aid them in climbing trees to hunt or escape danger. Interestingly, the opossum’s opposable thumb lacks a nail or claw.
The marsupial possums of Australia also have opposable thumbs. All but two possum species have a first and second toe on the forepaw that are opposable to the other three toes. The clawless first toe of the hindfoot is opposable as well.
9. Waxy Monkey Leaf Frogs
Waxy monkey leaf frog (Phyllomedusa sauvagii) in natural rainforest environment on a branch. They use their opposable thumbs to grasp tree branches as they move through the canopy.
Arboreal or tree-dwelling frogs of the family Phyllomedusa are one of only two non-mammals to make our list. These arboreal amphibians, which have a penchant for laying their eggs in a leafy parcel, can be found in Argentina and Panama.
Similar to monkeys and other animals, the frogs use their opposable thumbs to grasp tree branches as they move through the canopy. This is where they get their common names, waxy monkey leaf or tree frogs.
They also keep their skin moist with regular applications of a natural emollient secreted by their limbs which they pass over their backs to prevent dryness while branch-hopping.
10. New World Monkeys
White-faced Capuchin – Cebus capucinus, beautiful brown white faces primate from Costa Rica forest.
A few New World monkeys – those living in the Americas – have opposable thumbs. These include the saki, ukari, tamarin, woolly monkey, night monkey, owl monkey, capuchin, and squirrel monkeys. Like lemurs and lorises, some of these monkeys are classified as having pseudo-opposable thumbs.
Since New World monkeys evolved in South America, later migrating into Central America as well, they didn’t face competition from other monkeys. Consequently, a few of these small primates developed opposable thumbs and other distinct features, such as prehensile tails, which can grip things. Their noses are broader and flatter than Old World monkeys too.
