Human variation is highly non-concordant: many of the genes do not cluster together and are not inherited together. Skin and hair color are mostly not correlated to height, weight, or athletic ability. Humans do not share the same patterns of variation through geography. Dark-skinned populations that are found in Africa, Australia, and South Asia are not closely related to each other. Individuals with the same morphology do not necessarily cluster with each other by lineage, and a given lineage does not include only individuals with the same trait complex. Due to practices of endogamy, allele frequencies cluster by geographic, national, ethnic, cultural and linguistic boundaries. Despite this, genetic boundaries around local populations do not biologically mark off any fully discrete groups of humans. Much of human variation is continuous, often with no clear points of demarcation.