There are many different species alive on Earth but they all have some physical features in common. The study of the physical features and structure of an organism is called morphology.
Humans share many characteristics with our close relatives, other mammals. Some of these are obvious. We all have four limbs, two eyes, two ears, lungs and a skeleton.
But we also have features in common with more distantly-related species, including worms, and even single-celled organisms like amoeba.
This is evidence that all organisms on Earth, whether living or extinct, are related, and that we all evolved from a common ancestor.
Explore some examples of shared characteristics below.
The middle ear of mammals began as a jawbone, when animals felt the ground for vibrations instead of listening for sounds. Find out more.
Find out how the diaphragm lets horses and greyounds run so fast, and why mammals are more flexible than other animals.
Are mammals the only animals that have milk teeth and adult teeth? What happens when the adult teeth wear out?
Find out about the whale's moustache and ask whether humans really have less body hair than other mammals.
Find out how mammals keep cool and why they are the only organisms that sweat.
Find out why the panda's extra thumb isn't really a thumb at all, and why you have the same number of fingers as some dinosaurs.
From gills to lungs, find out how mammals, amphibians, reptiles and fishes breathe, and meet a relative of the lobe-finned fish that humans descended from.
What do you have in common with the aceol, a type of flatworm? Find out about humans' shared ancestry with organisms that evolved hundreds of millions of years ago.
What does the human body have in common with a single-celled organism? Find out about the features we share with early life forms that evolved billions of years ago.
Find out what humans have in common with the earliest single-celled organisms that emerged in the oceans billions of years ago, and with every other organism on the tree of life.
Compare the skulls of different hominid species to see how the human brain has evolved.