David; //What we need is a great big melting pot, fill it up to take the world and all it’s got.........pour out multi-coloured people. //
The problem with that idea is that you wouldn't have only multi- coloured people, you would spread out the human genome so much, and have an 'average' human being, no chess grandmasters, at least to compare with those of now, and no record-breaking athletes.
A human would be like a camel; a racehorse designed by a committee.