Vertebrates also include reptiles, amphibians, and birds. All vertebrates have an inner supporting skeleton, usually of bones, including a main backbone. The bodies of all vertebrates are organized on a two-sided body plan. This means that our bodies can be divided down the middle and are more or less the same on both sides. Mammals have warm blood, and fur or hair, and breathe air.
Most mammals have four limbs and are born rather than hatched.
Infant mammals are fed on milk, supplied by a mother. One thing that is very interesting about humans is the way we look. We all have slight differences in body shape, eye colour and shape, skin colour, facial features, hair styles, and weight. But these small differences are insignificant compared with the overall similarities in body shape and design, such as two arms, two legs, and one head, that we all share. Humans are able to express themselves as well.