Hold out your hand and look at your thumb. Touch the tip of each of your fingers with your thumb and think about all the ways you're able to grasp and manipulate objects using this amazing human "machine," the opposable thumb mechanism. (Opposable
means capable of being placed against or opposite something.)
Primates — chimpanzees, gorillas, orangutans, and humans, to name a few — share the common trait of hands designed with opposable thumbs. This adaptation is critical to the survival of monkeys and apes who gather and grasp their food as they make their way from tree to tree. Humans, who can move their thumbs a greater stretch across the hand than any other primate, rely on the ability to grasp to operate tools, such as eating utensils, pencils, screwdrivers, and sewing needles.
Now, think about your big toe. Can you move it all around to touch your other toes? No? What kind of primate are you, anyway? Unlike other primates, humans don't have an opposable toe structure, feet that function like hands for grasping. Opposable toes come in quite handy when monkeys or apes need to climb a tree or grasp a branch — either for leisurely dining or for quick escape from unwelcome visitors.
Primates aren't the only animals that depend on bendable digits. Opposums hang onto branches with the toes on their hind feet, and giant pandas use a part of their wrist bone like an opposable thumb to clutch tasty spears of bamboo — all in a day's work in a world of ever-evolving species!