* Tails are useful for balance and movement: Monkeys use their tails for balance, especially when swinging through trees. They can also use them to help them grab branches or reach for food.
* Humans and apes evolved differently: Over millions of years, our ancestors, who were tree-dwelling apes, started spending more time on the ground. This led to a change in their movement patterns. They began walking upright, which meant their tails were no longer necessary for balance.
* Loss of the tail: Through evolution, the tail gradually became smaller and less functional until it was completely lost. This is a common pattern in evolution where features that are no longer useful can disappear.
Important Note: Not all monkeys have tails. There are a group of monkeys called "New World monkeys" who live in Central and South America, that have prehensile tails, which means they can use them like a fifth limb to grab things. But apes (like gorillas, chimpanzees, and orangutans) and humans do not have tails.
Let me know if you have any more questions!