Mammals are animals who feed their young with milk from mammary glands and mostly give birth to their young alive. Mammals are vertebrate, which means they have backbones. They also breathe air, and have hair or fur. All mammals have a brain region called the neocortex, which other animals do not have. Most of the animals people keep as pets, like dogs, cats, and hamsters, are mammals. Most farm animals, like cows, sheep, goats, and horses, are mammals. In fact, biologists classify humans as mammals. There are 5,400 species of mammals all over the world. They range in size from Bumblebee Bats that are about 1 inch (30cm) long to Blue Whales that are 108 feet (33 meters) long. (Blue Whales are the largest animals that have ever lived on earth.)

Genesis, the first book of the Bible, says that before the flood Noah took every “kind” of animal on the ark to preserve them from drowning. The Hebrew word (miyn) translated “kind” is not a scientific word, and it doesn't correspond to our scientific classification of animals today. First Corinthians 15:39 can help us better understand the biblical meaning of “kind.” It says that there are four “kinds” of flesh: the flesh of people, mammals, birds, and fish. The Greek word used there may be translated “animal” or “beast” but it referred to what we call mammals. We don't know how many species of mammals there were in Noah's day, but we can be sure that there are many more today. The diversity of mammals is truly amazing.

All mammals have at least some hair, although some have much more than others, and it may be almost any color except blue or green. (Some mammals have hair that appears to be blue, but is actually gray. Polar bear fur sometimes appears to be green, but the color comes from algae.) Almost all mammals give birth to their young alive, but the platypus and echidna lay eggs and are exceptions to that rule. Most mammals are known as placental mammals and they give birth to their young fully developed. A small group of mammals called marsupials give birth to undeveloped young who develop inside a pouch on the mother's abdomen. Kangaroos are an example of marsupials. Almost all mammals are endothermic (warm blooded) meaning that their bodies maintain a steady temperature in spite of the surrounding temperature. The naked mole rat is a rare exception. (It also doesn't have much hair which may be why it doesn't maintain a good body temperature.) Mammals are not the only warm-blooded animals. Birds are also endothermic. Warm blooded animals have to eat more food for their size than cold blooded (exothermic) animals do because food supplies the energy to produce the heat. They also need a constant supply of oxygen to allow the metabolism processes to produce the heat.

By clicking on the buttons you can find out more about some of the many mammals in the world today.