Why is there only one human species?

[dipsydoodle]

Not so very long ago, we shared this planet with several other species of human, all of them clever, resourceful and excellent hunters, so why did only Homo sapiens survive?

Huge debates rage about human origins, but the broad consensus among scientists is that all the different species of human that have ever existed were descended from ape-like creatures that walked upright in Africa more than six million years ago.

These creatures had many descendants, most of which became extinct, but the first creature we would recognize as human first appeared in Africa two million years ago.

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Yet Homo erectus was slightly bigger and more powerful than Homo sapiens, so why did we thrive when they did not? The most obvious answer is that we had bigger brains - but it turns out that what matters is not overall brain size but the areas where the brain is larger.

http://www.bbc.co.uk/news/science-environment-13874671

For anyone who can get it :

Planet of the Apemen is on BBC1 at 2000BST on Thursdays from 23 June or catch up afterwards via iPlayer at the above link.