Elephants evolved to their current size over the course of tens of millions of years; this size adaptation is likely a survival mechanism because a full-sized, adult elephant faces very little threat from predators, though baby elephants are much more vulnerable to predation from big cats such as lions and wild dogs. There have been cases in which adult elephants have fallen victim to attack from big cats, but these cases are rare. The elephant is the largest known land animal, but scientists believe that this massive mammal evolved from a creature that is roughly the size of a small rodent.
An elephant's size in and of itself often functions as a defense mechanism. For example, adult Asian elephants have been observed forming a protective circle around younger elephants as a way of fending off predators. These large mammals may also walk in formations that put the largest family members at the extremities of the group as a means of protection. Elephants typically face their biggest threat from humans, which are able to use tools such as weapons to bring down large prey. It took elephants more than 20 million years to evolve to their current size. Size also plays a role in elephant social hierarchies, which could have an evolutionary impact as well.