Why are humans the only animals that faint from fear?

According to current knowledge, no other animal on Earth faints from fear like humans. Like many animals, humans' blood pressure will spike, pushing blood to the brain and increasing alertness when they feel they are in danger or experience an emotional surge.

But in humans, when the threat passes, the body sometimes overcompensates, causing blood pressure to drop too low and reducing blood supply to the brain. This is the reason why the person can lose consciousness for a moment, or in other words, faint.

Collapse also occurs in some other animals but is mainly due to unrelated muscle problems, humans are the only creatures that lose consciousness.

The cause is a unique combination of two human characteristics: upright posture and large brain. When people stand for a long time with the brain above the heart, blood must fight gravity to go to the brain. Besides, when standing still for too long, human legs with many blood vessels will capture a large amount of blood, making it even more difficult to provide enough blood to the brain.

Some other animals also have brains above the heart but do not require as much blood as the human brain. The human brain requires a lot of blood, accounting for up to 20% of the body's blood flow, while in our closest relatives it is less than 7% and in animals with smaller brains it is less than 1%.

Therefore, while for other animals, even if blood pressure drops sharply, the brain still receives enough blood to help them continue to run and jump, for humans, even a slight decrease in blood pressure can disrupt blood flow to the brain.

Falling puts the head and heart at the same height, helping blood quickly flow to the brain, but can sometimes cause serious injuries.