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While the Banzers may think of the work Matthew's grandmother and great-aunts do as mere baby-sitting, anthropologists know it is part of a far more primal practice called alloparenting. In all manner of animals, including bees, elephants, lions, lemurs, bats and birds, creatures with no parental investment in offspring routinely expend enormous amounts of energy caring for their relatives' young. Alloparents are not unconditional caretakers; they won't devote scarce resources to other offspring at the expense of their own. But when conditions allow an alloparenting deal to be made, it's a good bargain all around, with adults protecting their genetic legacy and the infant getting a team of surrogate moms in return. "Babies can learn to be quite satisfied with any of a select group of caretakers," says Hrdy, whose book Mother Nature is the most notable and artful of a flock of new studies re-examining motherhood.
Of course, even with a parade of alloparents, offspring will have little chance of reaching maturity if there isn't sufficient food to keep them nourished. In the game of survival, there is nothing more critical than keeping babies' bellies full, and mothers go to great lengths to get the job done. After one type of Australian spider lays her eggs, she lives barely long enough to see her young mature. Then she positions herself among them and slowly liquefies, transforming herself into an edible goo that gives her babies a nutritional kick start in life. The very idea of mammalian metabolism is a subtler case of maternal self-sacrifice. An organism taking in precious calories and then giving them away in the form of milk directly defies the me-first rule of all animal survival, yet mammal mothers do it willingly.
Often animals don't have to go to such nurturing extremes. For all creatures, one key to successful parenting is not merely reproducing but also knowing when not to reproduce--timing births so that the supply of food and other resources stay ahead of the babies to tend.
Heather Knotts, 35, of Chicago, a career mom, walks just this kind of parenting tightrope. Holding down a demanding job in an advertising agency, she works even harder at home, rearing a daughter, 5, and a son, 2. If Knotts and her husband had their way, she would set aside being adwoman and work full time as a mom. That was what they had planned. "After our first child was born, we knew I'd have to keep working," she says, "but we thought it would be for only a couple of years."
Three years after the Knottses had their first child, however, the second came along, and the idea of halving the household income while doubling the number of children it had to support was out of the question. The best Knotts could do was cut her workweek from five days to four, taking herself out of the running for promotions she had coveted but still not getting the round-the-clock time she wants with her kids.
As procreative strategies go, this seems an odd one. If you want to devote yourself exclusively to parenting, it's better to take your reproductive chips off the table after having one child so you can maximize the resources you have to do the job. If you want a multichild family, you'd better make sure that the family bank account is full to bursting.