An analysis of languages from around the world suggests that, like our genes, human speech originated -- just once -- in sub-Saharan Africa. Atkinson studied the phonemes, or the perceptually distinct units of sound that differentiate words, used in 504 human languages today and found that the number of phonemes is highest in Africa and decreases with increasing distance from Africa.
The fewest phonemes are found in South America and on tropical islands in the Pacific Ocean. This pattern fits a "serial founder effect" model in which small populations on the edge of an expansion progressively lose diversity. Dr Atkinson notes that this pattern of phoneme usage around the world mirrors the pattern of human genetic diversity, which also declined as humans expanded their range from Africa to colonise other regions.