Judy, the work you referred to was Erik Erikson's Childhood and Society, in
which he compared the childrearing practices of various Native American
nations.  One distinct difference was in the weaning practices.  Some weaned
at the time of the first teeth, as early as six months.  Others nursed three
or four years, one mother coming to school to nurse her six-year-old who had
a cold.  Erickson found a correlation between the culture's desired
expectation  of its adults and infant feeding practices.  It's interesting
reading.

Pat Gima, IBCLC
Milwaukee