There's a strange quirk of genetics that makes more sense the more you think about it. It goes something like this: the farther a population strays from where it started, the less diverse its genes. In other words, if a certain type of crane originally evolved in Mongolia, then millions of years later, its descendants that settled in Portugal will have a lot more genes in common with each other than the ones back in the motherland will. That's because the Mongolian cranes have the same diverse pool of genes that they've been working with this entire time, while the Portuguese cranes have only the genes of their ancestors that made the journey.
But what does this have to do with language? According to Dr. Atkinson and his team, the same principle applies to phonemes, the building blocks of language. A phoneme is basically the sound of a vowel, a consonant, or another sound (the word "bowl" has three—"b-", "oh", and "-l"). It turns out that languages that originate farther from Africa have consistently fewer phonemes. English has approximately 45 phonemes, while Hawaiian has only 13. The click-using languages of Africa, by contrast, can have well over 100. To many, this is evidence enough that humanity's ultimate mother tongue arose in the same continent where we first evolved.