Book 33, Question 105
What is an opposable thumb?
An opposable thumb is one that can swing across your hand and touch your other fingertips.
This lets you pinch, twist, and hold things tightly. Many primates have opposable thumbs. Try picking up a pencil without using your thumb, and you will see how helpful it is. Thumbs give primates fine control to peel fruit, hold tools, and groom.