human evolution website drawings Click to enlarge image
Illustration of a human skull. Image: Helen Beare
© Australian Museum

Human diversity

The hominin group contains both living and extinct human species as well as all human ancestors and relatives since the appearance of the first hominin 5–7 million years ago. Early hominins later evolved into diverse forms including early humans who appeared more than two million years ago. Two or more human species have often co-existed in the past but only one species has survived into the present day and that is our own species, Homo sapiens.

Human features – are we unique or are we immature apes?

Humans possess the same general features of mammals, primates and apes but we also differ in many ways. Some of these differences are physical while others are behavioural.

Physical features that are commonly used to separate humans from our closest ape relatives include:

  • rounded braincase with thin skull bones
  • high, vertical forehead
  • vertical face
  • small brow ridges
  • short jaws
  • centrally located foramen magnum (the hole in the base of the skull through which the spinal cord runs)
  • skull balanced on a vertical backbone
  • reduced hairiness

The physical features listed above are, however, also found in baby chimpanzees and other immature apes, which suggests that human evolution has involved the retention of juvenile features within adults. This evolutionary process is called neoteny.

Although many features of the human skull are reflected in the skulls of immature apes, many other features are unique to humans. These include:

  • extremely large brains relative to our body size
  • body structure that enables sustained movement on two legs (bipedalism)
  • short, blunt canine teeth
  • eruption of the canine teeth before the premolar teeth
  • projecting chin
  • speech
  • extremely sparse cover of body hair but a dense hair cover on the head
  • permanent enlargement of female breasts when mature
  • relatively short, straight finger and toe bones
  • long thumb that enables a precision grip
  • average life span that is longer than that of other apes
  • a lenghty period of development after weaning and a prolonged adolescence
  • complex tools are made and used
  • art, music, writing and other symbols
  • burial of the dead
  • transmission of cultural ideas, meanings and behaviours from one generation to the next
  • worldwide distribution