- What is this?
- What are the colours?
European - blue
African/African American - red
East Asian - yellow
Latino - green
South Asian - brown
- What do these dimensions mean?
- OK, so these are like genetic differences. What are they related to in the real world?
Long answer: for example, they are related to whether the individuals use chopsticks. Obviously, this is not because there is a genetic propensity to use chopsticks. These genetic differences come from groups' ancestry. But ancestry also affects other things, such as culture. So, it is more or less impossible to tell what these broad-sweep genetic differences actually cause.
That doesn't mean that some of the underlying differences don't have real world effects. We just can't tell what they are. To do that, you have to look at individual SNPs, or individual genes, and hold these principal components constant or control for them in some way.
The correlations can be quite amazing. The best known example is this picture of the first two principal components of a European population. It fits rather accurately on to a map of Europe, with people mostly shown quite close to their country of origin.
- Why are the East Asians so separate?
- What does this picture tell us?
- Who made it?