The development of dolphin's brain
For the last 47 millions years dolphin's brain has developed a lot. This conclusion was made after the rests of dolphins were discovered in some parts of the world.
Dolphins have the same correlation of the mass of the brain and the mass of the body as people do. That is why scientists consider that if they find out all the stages of development of dolphin's brain they will find the answer how people became so smart.
According to investigations dolphins are descended from some kind of four-footed mammals. And the analysis of the blood made scientists suppose that dolphins and horses are interconnected with each other somehow. Some time ago they returned to the sea (maybe it was connected with some catastrophe) and then they lost hind limbs and flippers appeared. Their length was about 9 meters. But then something happened and it is the mystery till nowadays, what really happened that these big dolphins disappeared and the new group appeared that substituted them.
Some scientists claim that dolphins came from people. But this theory is not popular among scientists that say that this story is too unreal to be real.