If you walked from Kerry to Capetown or Vladivostock (with the odd boat ride on the way, you'd see people changing all the way, but in a gradual kind of way. (McGrath)

Just for the fun of it, let's apply this type of argumentation to colours. Well, if you gradually 'walk' (you could do it with your computer) the colour scale from barely visible deep purple to barely visible dark red you'll see easily that there are no clear boundaries but only a gradual kind of change. So the concept of distinct colours has outlived its usefullness and we should give up using words describing different colours.

However, as for scientific application, I concur with McGrath. Same as in science words like 'red' and 'blue' are hardly used anymore (except in communication with nonscientists) since the knowledge about the underlying wavelengths was available, the concept of 'races' with its very crude and often varying definitions isn't usefull any longer since we know about differences describable in genetic terms.

And, BTW, an unbiased observer walking actually from Kerry to Capetown couldn't miss the fact that the gradient of change was much steeper for a few hundred miles of her walk, e.g. from the North of Tchad to the south of Tchad. Most of the whole change on the way would come within quite a small area south of Sahara.

Wolfgang