These Cro-Magnon people were identical to us: they had the same physique, the same brain, the same looks. And, unlike all previous hominids who roamed the earth, they could choke on food. That may seem a trifling point, but the slight evolutionary change that pushed man's larynx deeper into his throat, and thus made choking a possibility, also brought with it the possibility of sophisticated, well articulated speech. Other mammals have no contact between their air passages and oesophagi. They can breathe and swallow at the same time, and there is no possibility of food going down the wrong way. But with Homo sapiens food and drink must pass over the larynx on the way to the gullet and thus there is a constant risk that some will be inadvertently inhaled. In modern humans, the lowered larynx isn't in position from birth. It descends sometime between the ages of three and five months - curiously, the precise period when babies are likely to suffer from Sudden Infant Death Syndrome. At all events, the descended larynx explains why you can speak and your dog cannot.
( Bill Bryson )
[ The Mother Tongue: English and ]
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