You can make meaningful and consistent groupings in a continuum . For example you can make a distinction between poor and rich citizens, even tough the income d

You can make meaningful and consistent groupings in a continuum . For example you can make a distinction between poor and rich citizens, even tough the income distribution is a continuum. Same goes for the rainbow, the fact that it is continuous doesn't prevent people from being able to differentiate yellow and blue. But even so the human genome is not continuously distributed, even if the difference is linear with distance, simply due to the fact that humans are not continuously distributed geographically. You can't handwave oceans and mountains away. The main criticism of clustering is that the hierarchy of clusters that you obtain depend on the distribution of your samples, and that we currently do not have a good uniform sampling of human DNA. In short clustering can tell you reliably if someone is Irish or Italian, but may falsely identify the french as italian if there are not enough samples for french people.