“This capacity to maintain a long series of exhalations is unique to humans, thanks to bipedal locomotion. In quadrupedal animals like monkeys and apes, the shoulder locks the chest wall whenever the weight is on one arm during movement, and this means they can only take one breath per walking cycle. In humans, the arms are freed from weight-bearing, and so we are able to disconnect the breathing and walking cycles. This becomes important later for the evolution of speech, because this too depends on being able to sustain long, uninterrupted exhalations. Otherwise, we would end up with one-word sentences!”