Another suckling difficulty is the so-called ‘fighting at the breast’ response of certain infants. This often gives the mother the impression that the baby does not want to suck, but in reality it means that, despite desperate attempts to do so, it is failing because it is being suffocated. A slightly maladjusted posture of the baby’s head at the breast will block the nose and, with the mouth full, there is no way for it to breathe. It is fighting, not to avoid sucking, but for air. There are, of course, many such problems that face the new mother, but I have selected these two because they seem to add supporting evidence for the idea of the female breast as predominantly a sexual signalling device, rather than an expanded milk machine. It is the solid, rounded shape that causes both these problems. One has only to look at the design of the teats on babies’ bottles to see the kind of shape that works best. It is much longer and does not swell out into the great rounded hemisphere that causes so much difficulty for the baby’s mouth and nose. It is much closer in design to the feeding apparatus of the female chimpanzee. She develops slightly swollen breasts, but even in full lactation she is flat-chested when compared with the average female of our own species. Her nipples, on the other hand, are much more elongated and protrusive and the infant has little or no difficulty in initiating the sucking activity. Because our females have rather a heavy suckling burden and because the breasts are so obviously a part of the feeding apparatus, we have automatically assumed that their protruding, rounded shape must also be part and parcel of the same parental activity. But it now looks as though this assumption has been wrong and that, for our species, breast design is primarily sexual rather than maternal in function.
Leaving the question of feeding, it is worth looking at one or two aspects of the way a mother behaves towards her baby at other times. The usual fondling, cuddling and cleaning require little comment, but the position in which she holds the baby against her body when resting is rather revealing. Careful American studies have disclosed the fact that 80 per cent of mothers cradle their infants in their left arms, holding them against the left side of their bodies. If asked to explain the significance of this preference most people reply that it is obviously the result of the predominance of right-handedness in the population. By holding the babies on their left arms, the mothers keep their dominant arm free for manipulations. But a detailed analysis shows that this is not the case. True, there is a slight difference between right-handed and left handed females, but not enough to provide an adequate explanation. It emerges that 83 per cent of right-handed mothers hold the baby on the left side, but then so do 78 per cent of left-handed mothers. In other words, only 22 per cent of the left-handed mothers have their dominant hands free for action. Clearly there must be some other, less obvious explanation.
The only other clue comes from the fact that the heart is on the left side of the mother’s body. Could it be that the sound of her heart beat is the vital factor? And in what way? Thinking along these lines it was argued that perhaps during its existence inside the body of the mother, the growing embryo becomes fixated (‘imprinted’) on the sound of the heart beat. If this is so, then the re-discovery of this familiar sound after birth might have a calming effect on the infant, especially as it has just been thrust into a strange and frighteningly new world outside. If this is so then the mother, either instinctively or by an unconscious series of trials and errors, would soon arrive at the discovery that her baby is more at peace if held on the left, against her heart, than on the right.
This may sound far-fetched, but tests have now been carried out which reveal that it is nevertheless the true explanation. Groups of new-born babies in a hospital nursery were exposed for a considerable time to the recorded sound of a heart beat at a standard rate of 72 beats per minute. There were nine babies in each group and it was found that one or more of them was crying for 60 per cent of the time when the sound was not switched on, but that this figure fell to only 88 per cent when the heart beat recording was thumping away. The heart beat groups also showed a greater weight gain than the others, although the amount of food taken was the same in both cases. Clearly the beatless groups were burning up a lot more energy as a result of the vigorous actions of their crying.
Another test was done with slightly older infants at bedtime. In some groups the room was silent, in others recorded lullabies were played. In others a ticking metronome was operating at the heart beat speed of 72 beats per minute. In still others the heartbeat recording itself was played. It was then checked to see which groups fell asleep more quickly. The heart beat group dropped off in half the time it took for any of the other groups. This not only clinches the idea that the sound of the heart beating is a powerfully calming stimulus, but it also shows that the response is a highly specific one. The metronome imitation will not do—at least, not for young infants.
So it seems fairly certain that this is the explanation of the mother’s left-side approach to baby-holding. It is interesting that when Madonna-and-child paintings (dating back over several hundred years) were analysed for this feature, 373 of them showed the baby on the left breast. Here again the figure was at the 80 per cent level. This contrasts with observations of females carrying parcels, where it was found that 50 per cent carried them on the left and 50 per cent on the right. What other possible results could this heart beat imprinting have? It may, for example, explain why we insist on locating feelings of love in the heart rather than the head. As the song says: ‘You gotta have heart 1’ It may also explain why mothers rock their babies to lull them to sleep. The rocking motion is carried on at about the same speed as the heart beat, and once again it probably ‘reminds’ the infants of the rhythmic sensations they became so familiar with inside the womb, as the great heart of the mother pumped and thumped away above them.
Nor does it stop there. Right into adult life the phenomenon seems to stay with us. We rock with anguish. We rock back and forth on our feet when we are in a state of conflict. The next time you see a lecturer or an after-dinner speaker swaying rhythmically from side to side, check his speed for heart beat time. His discomfort at having to face an audience leads him to perform the most comforting movements his body can offer in the somewhat limited circumstances; and so he switches on the old familiar beat of the womb.
Wherever you find insecurity, you are liable to find the comforting heart beat rhythm in one kind of disguise or another. It is no accident that most folk music and dancing has a syncopated rhythm. Here again the sounds and movements take the performers back to the safe world of the womb. It is no accident that teenage music has been called ‘rock music’. More recently it has adopted an even more revealing name—it is now called ‘beat music’. And what are they singing about? ‘My heart is broken’, ‘You gave your heart to another’, or ‘My heart belongs to you’.
Fascinating as this subject is, we must not stray too far from the original question of parental behaviour. Up to this point we have been looking at the mother’s behaviour towards the child. We have followed her through the dramatic moments of birth, watched her feeding the child, holding it and comforting it. Now we must turn to the baby itself and study it as it grows. The average weight of a baby at birth is just over seven pounds, which is slightly more than one-twentieth the weight of the average parent. Growth is very rapid during the first two years of life and remains reasonably fast throughout the following four years. At the age of six, however, it slows down considerably. This phase of gradual growth continues until eleven in boys and until ten in girls. Then, at puberty, it puts on another spurt. Rapid growth is seen again from eleven until seventeen in boys and from ten until fifteen in girls. Because of their slightly earlier puberty, girls tend to outstrip boys between the eleventh and fourteenth years, but then the boys pass them again and stay in front from that point on. Body growth tends to end for girls at around nineteen, and for boys much later, at about twenty-five. The first teeth usually appear around the sixth or seventh month, and the full set of milk teeth is usually complete by the end of the second year or the middle of the third. The permanent teeth erupt in the sixth year, but the final molars—the wisdom teeth—do not usually appear until about the nineteenth.
Newborn infants send a great deal of time sleeping. It is usually claimed that they only awaken for about two hours a day during the first few weeks, but this is not the case. They are sleepy, but not that sleepy. Careful studies have revealed that the average time spent sleeping during the first three days of life is 16 hours out of every 24. Individuals varied a great deal, however, the sleepiest averaging 23 hours out of 24, and the most wide-awake a mere 10.
During childhood the sleeping-to-waking ratio gradually shrinks until, by the time the adult stage has been reached, the original sixteen-hour average has been reduced to half. Some adults vary considerably from this typical eight-hour average however. Two out of every hundred require only five hours and another two need as much as ten hours. Adult females, incidentally, have an average sleep-period that is slightly longer than that of adult males.
The sixteen-hour quota of daily sleep at birth does not occur in one long nocturnal session, it is broken up into a number of short periods scattered throughout the twenty-four hours. Even from birth, however, there is a slight tendency to sleep more at night than in the day. Gradually, as the weeks pass, one of the nocturnal sleep periods becomes longer until it dominates the scene. The infant is now taking a number of brief ‘naps’ during the day and a single long sleep at night. This change brings the daily sleep average down to about fourteen hours at the age of six months. In the months that follow, the short daily naps become reduced to two-one in the morning and one in the afternoon. During the second year the morning nap usually vanishes, bringing the average sleep figure down to thirteen hours a day. In the fifth year the afternoon nap disappears as well, reducing the figure still further to about twelve hours a day. From this point until puberty there is a further drop of three hours in the daily sleep requirement, so that, by the age of thirteen, children are retiring for only nine hours each night. From this point on, during adolescence, they do not show any difference from the fully adult pattern and take no more than eight hours on the average. The final sleeping rhythm, therefore, matches sexual maturity rather than final physical maturity.
It is interesting that amongst children of pre-school age, the more intelligent ones tend to sleep less than the dull ones. After the age of seven this relationship is reversed, the more intelligent schoolchildren sleeping more than the dull ones. By this stage it would seem that, instead of learning more by being more wide awake for longer, they are being forced to learn so much that the more responsive ones are worn out by the end of the day. Amongst adults, by contrast, there appears to be no relationship between brilliance and the average amount of sleep.
The time taken to fall asleep in healthy males and females of all ages averages about twenty minutes. Waking should occur spontaneously. The need for an artificial awakening device indicates that there has been insufficient sleep, and the individual will suffer for it with reduced alertness during the waking period that follows.
During its waking periods the newborn infant moves comparatively little. Unlike other primate species its musculature is poorly developed. A young monkey can cling tightly to its mother from the moment of birth onwards. It may even clasp on to her fur with its hands while it is still in the, process of being born. In our own species, by contrast, the newborn is helpless and can only make trivial movements of its arms and legs. Not until it is one month old can it, without assistance, raise its chin up off the ground when lying on its front. At two months it can raise its chest off the ground. At three months it can reach towards suspended objects. At four months it can sit up, with support from the mother. At five months it can sit up on the mother’s lap and can grasp objects in the hand. At six months it can sit up in a high chair and successfully grasp dangling objects. At seven months it can sit up alone without assistance. At eight months it can stand up with support from the mother. At nine months it can stand up by holding on to furniture. At ten months, it can creep along the ground on its hands and knees. At eleven months it can walk when led by the parent’s hand. At twelve months it can pull itself up into a standing position with the help of solid objects. At thirteen months it can climb up a set of stairs. At fourteen months it can stand up b itself and without supporting objects to help it. At fifteen months comes the great moment when, at last, it can walk alone by itself, unaided. (These are all, of course, average figures, but they act as a good rough guide to the postural and locomotory rates of development in our species.)
At about the point where the child has started to walk unaided, it also begins to utter its first words a few simple ones at first, but soon the vocabulary blossoms out at a startling rate. By the age of two the average child can speak nearly goo words. By three it has tripled this figure. By four it can manage nearly 1,600 and by five it has achieved 2,100. This astonishing rate of learning in the field of vocal imitation is unique to our species and must be considered as one of our greatest achievements. It is related, as we saw in Chapter One, to the pressing need for more precise and helpful communication in connection with cooperative hunting activities. There is nothing like it, nothing even remotely approaching it, in other closely related living primates. Chimpanzees are, like us, brilliant at rapid manipulative imitation, but they cannot manage vocal imitations. One serious and painstaking attempt was made to train a young chimpanzee to speak, but with remarkably limited success. The animal was reared in a house under conditions identical with those for an infant of our own species. By combining food rewards with manipulations of its lips, prolonged attempts were made to persuade it to utter simple words. By the age of two-and-a-half the animal could say ‘mama’, ‘papa’ and ‘cup’. Eventually it managed to say them in the correct contexts, whispering ‘cup’ when it wanted a drink of water. The arduous training continued, but by the age of six (when our own species would be well over the 2,000 word mark) its total vocabulary extended to no more than seven words.