Who Lies Sleeping?

Marine mammals have a most valuable reflex action when they go into a dive. Since they cannot breathe while underwater, they have to conserve oxygen. Their heart beat therefore automatically slows down. This is the diving reflex. Animals that are best adapted to the water, like the cetaceans, show it strongest, and, as far as anyone can tell, the reflex is not present in terrestrial species—though any poor creature thrown into deep water is likely to miss a heartbeat or two, so experimental results are not always conclusive. But, although man is terrestrial, he has a noticeably effective diving reflex. The heartbeat of a diving human slows down to half its normal rate of 72 beats per minute. This is an odd adaptation for a land animal!

Since the diving reflex is a mechanism for coping with a deficiency of oxygen, it has another aspect. It preferentially supplies oxygen to the brain which is soon damaged by lack of it. To do so more robust parts of the body are deprived of oxygen. This explains how people can sometimes be resuscitated after apparently drowning, especially in cold water, without suffering brain damage. Not all adaptations to diving have proved beneficial to mankind. Asthma is unknown in apes but in humans it mimics the constriction of the bronchial tubes in a diving seal. Diving is, of course, a stress. Asthma looks like a partial adaptation to diving that now manifests itself not under the stress of diving but under the different kinds of stress to which modern humans are subjected.

Human noses are also partially adapted to an aquatic life. They have become narrow, are supported at the tip by a bridge of cartilage, and have nostril flaps with muscles allowing them to be flared. A seal’s nostrils have similar muscles that are relaxed when the seal is submerged keeping its nostrils closed. On surfacing the muscles flex and the nostrils open to let the seal breathe. Plainly human forebears had begun to evolve the same means of preventing water from entering their breathing tubes.

Besides their developing ability to close their breathing tubes externally via the nostrils, humans can also block their nasal passages from their throat at will. This aspect of the aquatic adaptation has become an essential feature of speaking. It allows a subtle control of the expulsion of air over the larynx without which speech would be impossible. Thus the control of breathing required by a diving animal has helped humans to develop the power of speech by controlling the passage of breath through the larynx.

Rudimentary webbing can be seen between most people’s fingers and especially between the thumb and forefinger, but in about seven per cent of people it is pronounced enough to be regarded as ugly. Why should a line of mammals that have spent 60 or 70 million years in trees show even the slightest trace of webbing, an aquatic adaptation? There is no reason. Webbed hands are useful only for swimming.

Water compulsively attracts human babies. If babies younger than ten months old are put on a gentle slope leading into water they show every sign of being fascinated by this beautiful wet stuff. They explore the new medium, venture into it, show no signs of fear or panic, gaze about in wonderment with their heads underwater, are naturally buoyant, naturally hold their breath for long periods, naturally adopt a swimming position and quickly learn how to swim. After ten months these instincts are lost, the breath control goes because the child has not had cause to develop it. Older children and adults have to be taught how to swim.

Babies have been happily born underwater with apparent benefit to mother and child. Furthermore all terrestrial female mammals, even those that do not eat meat, eat their placenta after childbirth. Human mothers do not, and don’t seem inclined to, even if primitive or starving. Aquatic mammals also do not eat their placenta. They have lost the instinct simply because, after the aquatic birth, the afterbirth floats away to be lost while the mother is ministering to the needs of her new born child.

The coordination of group hunting as the drive behind the evolution of speech does not hold water. Mammals like wolves, hyenas and lions hunt cooperatively but have not evolved speech. Watch humans hunting. Far from shouting to each other they communicate by visual signals so as not to forewarn the game—or, in warfare, the enemy. Other than man the creatures that have developed vocal communication furthest are the whales and dolphins. The reason is that visual communication is hampered by the water.

Dolphins have a wide range of sounds, many being whistles. If two dolphins start whistling at the same time, one will stop until its companion finishes, then it will resume. It seems as though they are taking it in turns to listen to each other and to speak—they seem to be conversing. But is there any proof? In behavior experiments, dolphins are not allowed to see each other but are allowed to hear. Yet if one is shown a lever to press to get a reward the other one knows too. They seem to be telling each other which levers to press to be rewarded. Richard Mark Martin concludes, “tasks… were accomplished by the dolphins with so much assurance that it was obvious they did indeed have a language…”

Humpback whales, which can articulate about 20 different sounds, are so sophisticated in language that they “speak” in rhyme. Two US researchers, Linda Guinee and Katherine Payne, came to this conclusion after listening to countless hours of taped humpback whale sounds. A third of the whales’ song consisted of rhyming sections. Consecutive passages tend to end in similar sounds even though the rest of the song is quite different. Whales in one part of the ocean use the same rhymes but the rhymes change with time, showing that they are not instinctive like birdsong. Humans find rhymes so compelling that they cannot get certain rhymes and jingles out of their heads. Advertisers play strongly on this. Possibly the rhymes help the whales to remember the songs which act as social cement within the groups. For whales, the rhymes are most common in the more complicated songs—the ones most difficult to remember.

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