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The Grasping Hand

Part of Hall of Human Origins.

The grasping hands of primates are an adaptation to life in the trees. The common ancestors of all primates evolved an opposable thumb that helped them grasp branches.

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© AMNH Exhibitions

As the grasping hand evolved, claws disappeared. Today, most primates instead have flat fingernails and larger fingertip pads, which help them to hold on. The hands of many higher primates can grasp and manipulate even very small objects.

What makes human hands unique?

The human opposable thumb is longer, compared to finger length, than any other primate thumb. This long thumb and its ability to easily touch the other fingers allow humans to firmly grasp and manipulate objects of many different shapes. The human hand can grip with strength and with fine control, so it can throw a baseball or sign a name on the dotted line.

Where's the thumb?

When moving quickly through the trees, spider monkeys use their hands like hooks and swing from branch to branch. Spider monkeys have evolved an extremely small thumb bone--a full-sized thumb would hinder their swinging.

Like a Fifth Hand

The spider monkey's prehensile, or grasping, tail can support its entire body weight. Each monkey has a unique pattern of lines on its tail, like a fingerprint, which helps the tail to grip branches.

Slow Life

For most mammals, the bigger the species, the slower it grows and the longer it lives. Primates take this pattern to the extreme, with even longer lives and slower growth rates, both in the womb and after birth.

Slow growth may have evolved because it gives young primates more time to learn complex social behaviors. And it may foster the development of another classic primate feature--an unusually large brain.

One fast monkey

Although primates grow slowly, they aren't slow in every way. Patas monkeys can run at speeds up to 34 miles an hour! The fastest human sprinter reaches only 27 miles an hour.

The Great Brains

Among mammals the general rule is: the bigger the body, the bigger the brain. But the brains of most primates are a lot larger than one would expect based on their body size. The average talapoin monkey (Miopithecus talapoin) weighs only one-tenth as much as an African porcupine (Hystrix cristata). Yet their brains are almost exactly the same size.