Evolution And History

Food Production and Population Size 243

Biocultural Connection

Breastfeeding, Fertility, and Beliefs

Cross-cultural studies indicate that

farming populations tend to have higher

rates of fertility than hunter-gatherers.

These differences in fertility were cal-

culated in terms of the average number

of children born per woman and through

the average number of years between

pregnancies or birth spacing. Hunter-

gatherer mothers have their children

about four to five years apart while some

contemporary farming populations not

practicing any form of birth control have

another baby every year and a half.

For many years this difference

was interpreted as a consequence of

nutritional stress among the hunter-

gatherers. This theory was based in

part on the observation that humans

and many other mammals require a

certain percentage of body fat in order

to reproduce successfully. The theory

was also grounded in the mistaken

cultural belief that the hunter-gatherer

lifestyle, supposedly inferior to that of

“civilized” people, could not provide

adequate nutrition for closer birth

spacing.

Detailed studies by anthropologists

Melvin Konner and Carol Worthman,

among the !Kung or Ju/’hoansi people

(also, “Bushmen”) of the Kalahari Des-

ert in southern Africa, disproved this

theory, revealing instead a remarkable

interplay between cultural and biological

processes in human infant feeding.

Konner and Worthman combined

detailed observations of Ju/’hoansi in-

fant feeding practices with studies of

hormonal levels in nursing Ju/’hoansi

mothers. Ju/’hoansi mothers do not

believe that babies should be fed on

a schedule, as recommended by some

North American child-care experts, nor

do they believe that crying is “good”

for babies. Instead, they respond rap-

idly to their infants and breastfeed

them whenever the infant shows any

signs of fussing during both the day

and night. The resulting pattern is

breastfeeding in short, very frequent

bouts.

As Konner and Worthman document,a

this pattern of breastfeeding stimulates

the body to suppress ovulation, or the

release of a new egg into the womb for

fertilization. They documented that hor-

monal signals from nipple stimulation

through breastfeeding controls the pro-

cess of ovulation. Thus the average num-

ber of years between children among the

Ju/’hoansi is not a consequence of nutri-

tional stress. Instead, Ju/’hoansi infant

feeding practices and beliefs directly

affect the biology of fertility.

BIOCULTURAL QUESTION

From both evolutionary and child de-

velopment perspectives, what might be

the advantages of breastfeeding babies

for the first few years of life? What cul-

tural processes work against this in your

culture?

a Konner, M., & Worthman, C. (1980).

Nursing frequency, gonadal function,

and birth spacing among !Kung hunter-

gatherers. Science 207, 788–791.

The higher fertility of the Amish, a religious farming culture in North America, compared to that of the

Ju/’hoansi hunter-gatherers from the Kalahari Desert, was originally attributed to differences in nutrition.

It is now known to be related to differences in childrearing beliefs and practices.

© Dennis MacDonald/PhotoEdit © Irven DeVore/Anthro-Photo

Indian

Ocean

Atlantic

Ocean

ZIMBABWE

ZAMBIA

SOUTH SWAZILAND

AFRICA

NAMIBIA

LESOTHO

BOTSWANA

Ju/’hoansi

KALAHARI

DESERT

ANGOLA

TANZANIA

MOZAMBIQUE

MALAWI

DEMOCRATIC

REPUBLIC

OF CONGO