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What Are the Functions of a Primate's Thumb?

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There are numerous primate species in the world, and they all have thumbs. But the actions and movements these thumbs allow varies as greatly as the species themselves. From grasping, climbing, hanging, peeling, throwing, fishing and even creating tools, having a thumb opens a whole new world of dexterity.

Thumbs Are Handy

Humans rely on their thumbs to pick things up, write things down, button clothing, tie shoes and much more. Nonhuman primates use their thumbs for a range of purposes as well, and different primate species have different kinds of thumbs with varying degrees of dexterity and motion. Some primates have the kinds of thumbs that let them create and use tools. While all primates have thumbs, not all primates are able to actually use them.

Opposable Thumbs - Efficient Object & Tool Usage

Humans have what are known as opposable thumbs. This means the thumbs can move and rotate independently of the other four fingers. Some primate species share this feature with humans, assisting them in grasping, manipulating and handling objects more efficiently. Opposable thumbs also assist in the creation and usage of tools, and the development of fine motor skills. Primates with opposable thumbs include great apes -- chimpanzees, bonobos, orangutans and gorillas -- and Old World monkeys like baboons and Colobus monkeys.

Non-Opposable Thumbs - Grasping, Hanging

Naturally, primates who don't have opposable thumbs have non-opposable thumbs. Like opposable thumbs, non-opposible thumbs are used to grasp objects and peel fruit. Primates also use them to hang onto tree branches by hooking their thumbs on them. Non-opposible thumbs, while quite handy so to speak, don't have the efficiency of opposible thumbs when it comes to developing tools, pinching objects between the index finger and thumb, and even using silverware like apes can, if given the chance.

Throwing, Clubbing, Fishing

Richard W. Young's 2003 "Journal of Anatomy" article, "Evolution of the Human Hand: The Role of Throwing and Clubbing," notes humans and some apes -- with their opposible thumbs -- can throw and swing objects like clubs. In doing so, they use different thumb grips, including the "precision grip" and "power grip." Apes who can grasp long sticks can also use them to fish out ants or other insects from areas too deep to reach by hand.