Once upon a time, humans could not hold conversations or sing songs together. Now we chatter incessantly, not only with speech but also through text messages, tweets and status updates. How we transformed into the highly social species we are today remains the subject of many theories.

Two competing hypotheses center on whether our capacity for language is an innate skill that grew stronger through natural selection or whether we lacked any such ability and instead trained our brains to collect new information using objects and sounds in our environment. In his new book Harnessed, Mark Changizi stakes out the middle ground: cultural—not natural—selection explains our language ability.

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