Whales are mammals, just like humans, and their evolutionary ancestors walked on land as we do. Over 50 million years, the ancient creatures spent more and more time in the water, and eventually, stopped coming to land altogether. The transition from land to sea may seem strange, but the best guess is that the whale's ancestors simply went where food was plenty - the ocean. So they evolved in a way that let them live in the ocean, with wide tail flukes, extended flippers and, in some species, dorsal fins.

They also had to develop breathing techniques that allow staying underwater for long periods of time without coming up for air to swim, hunt, and communicate. To do this, they developed a highly specialized breathing system. A whale's lungs work like ours do, but they make the most of each breath. In one breath, a humans body can absorb about 15 percent of the oxygen inhaled. The whale, on the other hand, absorbs as much as 90 percent of the oxygen it breathes in.

Whales store this excess of oxygen in myoglobin, a special protein cell found in muscles. Whales have greater amounts of myoglobin than other animals, allowing them to store larger amounts of oxygen at a time.

Whales also make more efficient use of this oxygen. When they dive, their heart beats more slowly and select arteries are constricted. This slows the flow of blood to certain organs without decreasing blood pressure. This way each breath last longer.

The sperm whale's respiratory system is among the most efficient in the world -- it can hold its breath for 80 to 90 minutes at a stretch. The beaked whale can swim without a breath for as long as two hours.

A whale's "nostrils" are called blowholes and are on the top of its head. Some whales have one blowhole and others, like this blue whale, have two. Since they can only breathe at the surface, whales have had to develop conscious or voluntary breathing. That means they choose when to take a breath. This is important because whales can't breathe underwater. So they surface every few minutes to blow out a mixture of water and air and take in a breath of fresh air.