by Ashley Montagu
Human kids and kangaroo kids have more in common than you might think. By studying marsupial mothering, researchers are gaining valuable new insights into the needs of vulnerable newborns.
A human body is not a finished product. The newborn elephant and the newborn fallow deer can run with the herd shortly after they are born. A six-week-old seal navigates the seas by itself. Human beings, however, can't even crawl until they are 8 to 10 months old; they can't walk or talk until they're about 14 months old. Why are human beings born more immature and why do they stay immature longer than any other animal?
Like the newborn marsupial that crawls over its mother's damp fur to her pouch, there to spend up to six months completing its development, the human newborn is only half-formed. It could be said that a child's birth is not an end of gestation but a bridge between growth within the womb and growth outside it. The elephant, deer, seal and human all have long gestation periods – ranging from an average period of 630 days for the elephant to about 266 days for humans. Yet only humans are born so immature, their growth divided into a period inside the womb (uterogestation) and a period outside the womb (exterogestation). It appears that if babies weren't born when they are, they couldn't be born at all.
At birth, the brain of the average seven-pound infant weighs roughly 380 grams. To be as talented and capable as a newborn elephant, deer or seal, the human infant would need the 825-gram brain of a one-year old. Clearly, infants can't wait until they've grown a brain that big before being born – their heads would be too large to fit through the mother's birth canal. They must be born with the biggest possible brain that still allows them to get out and then do the rest of their brain-growing after birth.
As Professor John Bostock of the University of Queensland, Australia, suggested, what I call the period of exterogestation is over when a child can crawl on all fours. Amazingly, the average time for this achievement is 266 days – exactly the same length as the average pregnancy.
Two-stage gestation might have been an adaptation to several important changes during the early evolution of the human species. The move from the forest to the open plains demanded an erect posture and a bigger brain. The pelvic outlet grew smaller while the brain grew larger.
If this two-stage theory of gestation is sound, then we are not adequately meeting the needs of infants. We fail to give attention to gestation outside the womb.
The human infant is almost as immature as the infant opossum or kangaroo, but whereas the marsupial infant enjoys the protection of its mother's pouch, the human infant has no such advantage.
The symbiotic relationship maintained by mother and fetus throughout pregnancy should not end at birth; indeed, it is naturally designed to become more intense during exterogestation. The mother who is equipped to give sustenance and shelter inside the womb is equipped to do so outside the womb, at least as efficiently as the marsupial mother.
The warmth with which the mother enfolds her child while breast-feeding is psychologically analogous to the pouch enclosing a suckling marsupial. However, little marsupials, with free access to their mother's breast, suckle when they wish; human infants are generally suckled when their mothers think they should be. Children are therefore in a much more dependent, indeed more hazardous, state than marsupials; they should be nursed on demand, rather than by the clock.
When the human mother breast-feeds her child, the pair make eye contact vital to the psychological development of the child. The mother lovingly coos, talks and sings to the child, cuddling, kissing and caressing it. As important as breast-feeding itself are its associated sensory stimuli – the sights, sounds, smells, taste and warm feelings that comprise the enfolding love that ought to be the birthright of every child.
Several studies show that early deprivation of maternal care leads, in many animals, to failure of both individual and social development. The human infant is in many ways more dependent on such sociopsychological care, not merely because it is born in such an immature state, but because becoming a competent human being is much more complicated than becoming a competent baboon.