As far as birth-spacing goes, nomadic situations make frequent birthing maladaptive. Every time a !Kung woman moves, she must carry all of her children who are less than four years old. Over a four-year period, she will carry a child nearly five thousand miles. If she has a child as early as two years after the previous one, it will be a tremendous burden. Prolonged lactation is a major factor in maintaining birth spacing, and hg behaviors pertaining to child-rearing reinforce this natural contraceptive mechanism. In some groups, lactation can last as long as four years, especially because hgs don't have soft foods available for infants like agropastoralists do (i.e. grain and milk). The availability of such foods leads to earlier weaning and resumed ovulation (Lee 1972; Lee 1980). Indeed, once sedentism occurs, and social dynamics become more complex, a woman can shorten the interval between births and still give each child adequate care as she is now required to carry her children much less often. Sedentism therefore acts as a mechanism generating population growth, and forcing early weaning.
The impact this has on child rearing is easy to imagine -- the pain of earlier weaning and sibling rivalry is quite traumatic. The wide birth spacing of the nomadic !Kung means each child gets its mother's (and family's) attention for forty-four months, thirty-six of which includes breast feeding. A child weaned at twelve months instead of thirty-six is going to have quite a severe trauma of separation. "This pattern of much earlier weaning among agricultural peoples is a crucial distinction between them and HGs. This wide birth spacing typical of HGs enables 'the raising of what might be called fewer children of higher quality.' Prolonged lactation and holding and the absence of sibling rivalry mean better care and greater psychological stability; and one sees this stability among !Kung adults," writes Berman.
It is lactational amenorrhea (lack of menstruation during breast-feeding) that contributes to keeping birth spacing wide for hgs. As stated above, for some groups, like the !Kung, the period between births can be up to four years in length. One study showed that bottle-feeding women began to menstruate eight weeks after delivery, whereas breast-feeding women menstruated after thirty-three weeks. No woman in the sample ovulated if she were breast-feeding more than five times per day or for a total of more than sixty minutes per day (Short 1984, Thapa et al. 1988). This is typical among hgs. For the Hadza, Marlowe (2010) calculated the median age of weaning to be 2.5 years (1-3 years, n=33). A few children nurse until they are three years old, but most nurse at lower frequency by age two. A small number of children have been known to protest loudly as late as the age of three when their mothers refuse to nurse them (Marlowe 2010). Clearly, the Hadza have a much lower age of weaning than the !Kung do, and we mustn't let the higher figures create a bias in that direction. The !Kung are leaner than most hgs, and this lack of body fat contributes to prolonged lactational amenorrhea, which puts them at the low fertility end of the spectrum (Cashdan 2009). However, the Hadza are pretty low on the fertility scale compared to most civilized nations. According to the CDC, an average of 75% of infants have already been fully weaned by twelve months of age in the United States. The same study showed that over twenty percent of the population has never breastfed at all. So the Hadza, then, despite their relatively high fertility for hgs, are still representative of a very different set of rearing practices than their civilized counterparts.
"The power of all of this in biological and demographic terms is important to keep in mind because it strongly suggests that the Neolithic configuration of sedentism, population pressure, food accumulation, frequent birthing, and early weaning -- factors that I personally believe enhance human insecurity and are behind the drive for dominance and hierarchy -- is very recent in human history and quite unnatural," Berman explains.
That takes us to one of the subjects we all have in common: death. Hgs have very simple beliefs regarding death, beliefs that are quite unnerving to many civilized people. For hgs, the focus is on this life; the "sacred" is merely what is present around them. They do not believe in prophets or guru figures; "worship" is nothing more than participation in the here and now. Hgs tend to think of death as no big deal. The Hadza don't mark their grave sites; many of them say that when one dies, one simply rots, and that's it. Similarly, the Baka don't believe in an afterlife, ghosts or spirits. They say: "When you're dead, you're dead, and that's the end of you." Until recently, they left their dead in the forest to be eaten by animals. As for the Mbuti, when missionaries or agricultural neighbors approach them about the afterlife, they say: "How do you know? Have you died and been there?" None of these groups has a chief or shaman to administer any death ritual. One can see that death was not scary, and not something to neurotically dwell on, for most hgs. They simply regarded it as another part of life, and focused on living.
This section has been something of an exploration of the drivers of hg psychology. While there is not as much hard evidence to go on as one would like, I believe we have pieced together an appreciably valid and instructive approach toward understanding the subject a little better than we did before. I think a little insight has been gained into the nature of the contrast between hg and civilized cultures, and hopefully this can be a constructive beginning in understanding who we are -- and who we were.
We are now at a close. I hope this journey has been as informative and stimulating for you as it has been for me. Thanks for reading.