Natives living in typically 'harsh' conditions: do any have low infant/child mortality rates?
"Newborns are particularly susceptible to shortfalls in caloric intake. They are dependent on their mother’s milk for calories. I know the agricultural diet is nutritionally deficient, I’m not gonna argue that it is. The farmers’ diet has made us less robust and susceptible to dietary diseases. But it is rich in calories and the greater accessibility to calories that come with agriculture improves likelihood of young children reaching sexual maturity."
from this article http://anthropology.net/tag/infant-mortality-rates/
In the societies listed in that site, 1 out of 3 babies not making it to age 1 seems to be pretty consistent. Pretty bleak by today's standards.
According a graph on Don Matesz's site, the Yanomamo do a little better though.
I think the hard thing to figure out here is if hunter-gatherer's were always as food insecure as they are today. If hunting was generally good, and nutrition somewhat stable, I'd think the infant mortality rate would be much lower.
Wish I had an answer that painted a rosier picture.