The earliest languages may have been click languages such as those of the San (Bushmen) of southern Africa and the Hadzane of Tanzania. These languages use not only vowels and consonants but also clicking sounds. The Hadzane live about 1,200 miles (2,000 km) from the San, and their language is unrelated to San except for the use of clicks. The split between Hadzane and the San languages may have occurred as long as 50,000 years ago, perhaps the oldest divergence in the evolution of extant languages. Anthropologists suggest that the primordial human language used clicks because click sounds, unlike voice sounds, can be used during hunting without scaring the prey away as a verbal language would. Some speakers of these languages sometimes just use clicks, with no verbal components, as if the verbal component is a later addition.

Humans spread all over the world from their African homeland. Once a tribe had a language that was their identity, they were unlikely to change it. As tribes migrated, and displaced or conquered other tribes, they took their languages with them. Languages have changed tremendously, and people have evolved slightly, since that time. Most of the genetic patterns that have resulted from recent human evolution consist of minor genetic variation. Luigi Luca Cavalli-Sforza, a geneticist at Stanford University, has found a rough correlation between human genetic markers and languages. The major language groups correspond roughly to the major genetic groups.

Sometimes the correspondence between language and genetics is quite close. Both genetic markers and languages spread along with agriculture: Indo-European languages in Europe, Sino-Tibetan languages in China, and Niger-Congo languages in Africa. The linguistic association of Apaches and Navahos (Na-Dene) to the Athapascans of the Pacific Northwest is mirrored in the similarity of their mitochondrial DNA. The linguistic association between the Romany and Hindi languages cleared up the historical enigma of where the Gypsies came from, over a century before DNA tests could demonstrate the same thing. The Gypsies are apparently a tribe that left India and migrated into Europe about 2,000 years ago.

Sometimes the correspondences between languages and genes in human history are not as close or not necessarily reliable. Some of the language families that Cavalli-Sforza used in his analysis, such as Australian and (Native) American, are not linguistically related groups but geographical clumps. The American languages are of recent origin (probably the past 13,000 years) but constitute many linguistic families, while African languages are the oldest but constitute far fewer linguistic families.

Linguistic diversity has developed through the same two processes, vicariance and dispersal, that have stimulated the development of geographical patterns of species . . .

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