145 The Primate Hand

Key Idea: Primates have grasping hands, but the human hand is particularly developed with respect to dexterity and the manipulation of objects. Primates have a grasping hand. They are able to pick things up, hold, and manipulate them, although the degree to which a primate can do this depends on the species. Humans have a highly advanced ability to manipulate objects with their hands because the thumb is very long relative to the hand.

Index finger and little finger are able to pivot and move towards each other, allowing the fingers to form around small objects.

Large muscles, especially around the thumb, produce a powerful grip.

3D

Flexible joints in the hand allow it to flex, increasing dexterity.

Chimpanzees are very capable tool users, but their dexterity is limited by the length of their hand compared to the thumb and the rigid wrist bones that limit wrist rotation.

Grips of the human hand

LBS The fingers have end tactile pads that contain huge numbers of nerve endings, producing a highly sensitive surface.

Nails are found on at least some digits in all modern primates.

Highly mobile thumb, able to touch all other fingers on the hand.

New research suggests manipulating objects may not have been the only important factor in the evolution of the human hand. The human hand shape is one of the only configurations possible that maintains dexterity while allowing the hand to form a fist. Although a punch with a closed fist produces the same force as a slap with an open palm, a punch delivers the force to a smaller area, producing a much greater impact and potential for damage to an opponent.

Precision/ power grip Power grip Power grip

1. Name two possible selective pressures acting on the human hand:

2. Explain why being able to manipulate objects is an evolutionary advantage:

3. Identify two features that make the human hand so dexterous and compare them to a chimpanzee hand:

Precision grip