Humans are not the only animals with opposable thumbs. Most (but not all) species of primates have thumbs, as well as certain species of frogs, rats, mice, lemurs, birds, pandas, and even dinosaurs. The opossum does, and also the chameleon.

But in humans, it made all the difference. “Increased manual dexterity in the form of efficient thumb opposition was among the early defining characteristics of our lineage, providing a formidable adaptive advantage to our ancestors,” says paleo anthropologist Katerina Harvati. The thumb has been described as “mankind’s greatest app.”

The development of the opposable thumb allowed humans to hold and manipulate very tiny things while also gripping large unwieldy things. In short, the thumb offers both the power grip, and the precision grip.

The first opposable thumbs appeared in Homo erectus (“upright man”) about 2 million years ago. Then came Homo habilis (“handy man”) who were the first to create tools. Finally, there was Homo sapiens (“wise man”).

The Boot Shop Outlet

Creating and using tools opened up new food sources. A rock could be thrown; a spear could be hurled; a club could kill a wounded animal; a flint knife could prepare the evening meal.

The Latin word “phalanx” means “armed men in battle array.” The bones in the fingers are named “phalanx” (meaning a single bone) or “phalanges”(for multiple bones) because when the fingers are together, the bones line up like soldiers ready to fight.   

The difference between the four fingers and the thumb is that the fingers have three bones, or phalanges, whereas the thumb only has two. Fingers have three joints; thumbs have only two.

The joint that joins the thumb to the hand is called a saddle joint, and allows the thumb to rotate in ways the fingers cannot move. The thumb is the only digit that can touch every other digit on the hand.

The thumb has nine muscles: four of them are located in the forearm, and five are located in the hand. None are in the thumb itself.

When someone loses their thumb, it can be skillfully surgically replaced either by the big toe, the second toe, or the index finger. The index finger is the digit that does the least amount of work. The thumb, by contrast, carries 40% of the workload. The thumb does as much work as the combined middle finger, ring ringer, and pinky finger.

When you see medical personnel taking a person’s pulse on the neck, they use the index and middle fingers together. The thumb is never used for this purpose because an artery running through the thumb has a strong pulse of its own, which would lead to false readings if people were counting their own pulse by mistake.

The word “finger” springs from the word meaning “five.” “Tum” was the word meaning “swollen” and may be the origin of the word thumb. No one is certain why the word thumb ends in a B, but linguists say it happened in the late 13th century, about the time that dumb, numb, and limb also acquired a silent B.

The thumb is used in American vernacular in a variety of phrases. We have the rule of thumb: we thumb a ride; we are under somebody’s thumb; we give thumbs up or thumbs down; thumb our noses; sketch out a thumbnail; thumb through a book; and we are all thumbs, or we have a green thumb.

Julius Caesar ordered the thumbs of captured prisoners to be cut off so they would never again be able to wield a sword.