This books tells the story of how human beings came to be human beings through acquiring language and explains the physical properties of the human brain, larynx, tongue, etc. which allow the necessary flexibility to create the range of sounds which constitute human speech. Professor Lieberman explains the different between male and female speech in human society as a differentiation between formant frequencies. Most little boys unconsciously learn to talk with their lips somewhat pursed, which gives them lower formant frequencies, even though their airways are no longer than those of little girls. He also has answers for the snarl of the dog and the diminution of speech capacity on top of Mount Everest. One factor that clearly sets human beings apart from other living animals is the effect of culture on the behaviour of individuals.
Culture evolves around a sense of what is desirable behaviour and what is undesirable.
One unfortunate consequence of this more subtle basis for human morality is its Manichaean cast - it can yield behaviour both for good and evil that transcends the capacity of any other animal. The cognitive basis of this higher human morality is simple. We can place ourselves in the position of the 'other' and through the medium of language convince others. History is cited to demonstrate the cognitive-linguistic basis of human morality. The Mongols were at one point in history adept at placing themselves in the position of the 'other' and doing whatever was needed to terrify their adversaries into surrender.