Hominin Evolution Chapter 15 – Part 1

Classification of Humans

Humans are mammals Mammals are vertebrates (backboned animals) whose female members have mammary glands. They are characterised by having fur or hair, and also by having three characteristic bones in the middle ear. There are approximately 4,260 species of mammals.

Humans are Primates

What is a primate? Primates are characterised by having 5 digits on fore and hind limbs, and also opposable thumbs. Nails on the fingers and toes. Stereoscopic 3D colour vision. Relatively flexible skeletons. A large brain compared to skeleton size.

Humans are Hominoids

What is a hominoid? Any human-like species, including us. Bipedal (walks on two legs). Intelligent (large brain size, uses tools).

Humans are hominins At this level of classification, Humans are separated from all other great apes. This group is characterised by the ability to walk upright. The ability to walk upright is called Bipedalism.

Footprints Fossilised footprint evidence can provide evidence of how a species walked at a particular time. The footprints on the right were found in Tanzania in 1978 in a place called Laetoli. They are the footprints left behind by a species within the Australopithecus species 3.5 million years ago.

Evolution of the primates Over a long period of time, the genetic differences that accumulate within a subspecies may result in individuals that are significantly modified structurally, physiologically, or behaviourally. The differences among some subspecies may be so great that they reduce reproductive success when the subspecies mate. This is called Speciation. The species that gave rise to these new species is called a common ancestor.

When did the ‘human’ line diverge It is thought that the human line diverged from other apes about 4 million years ago. This calculation is based on evidence obtained using the “molecular clock”. It has also been confirmed by more recent comparative studies of DNA.

Hominin Evolution: Where Did It Begin? Hominin evolution began in Africa 5-7 million years ago. In Africa most of the fossils found have been of the Australopithecus genus. It is thought that individuals of the genus Homo were the ones who migrated outside of Africa, and hence gave rise to populations all over the world. Although evolutionary biologists have a good understanding on the theories of how humans evolved, there is still evidence which is being found and changing our interpretations. It is important to remember that evolutionary biology is not static and it relies heavily on the quality and quantity of fossils available to biologists.