On Sun, 30 Jan 2005 10:32:48 -0500, Janice Berry Paganini <[log in to unmask]>
wrote:

>Apologies if this has already been mentioned. I don't remember seeing this
>come up.
>http://www.newscientist.com/article.ns?id=dn6921
>
>Janice Berry
>Westerville, OH
>

I read the article.  Sounds like a far stretch of the imagination to me.

Here are my objections--

"A taste for meat prompted early humans to wean their children at a young
age. The idea explains why we now wean our infants years earlier than other
great apes."

-- Chimpanzees kill monkeys and eat them when they get the chance.  In some
human societies, weaning is at four or later with tandem nursing not
uncommon.


"In non-industrialised societies, women breastfeed their children for an
average of two and a half years, while chimpanzees feed theirs for five.
Anthropologist Gail Kennedy of the University of California, Los Angeles,
US, suggests that humans made the transition to early weaning 2.6 million
years ago.

-- How was the average weaning age for non-industrial societies arrived
at?  Did they factor out influence from industrialized countries?  Those
influences would not have been present in pre-historic times.
Acceptable weaning age depends greatly on local custom.  We don't know what
the custom was among early humans.


"That was when a branch of hominids began to eat animal carcasses - a risky
activity that would have brought them into contact with other predators and
significantly raised mortality rates for the hunters."

-- Among social animals, it is common for one or two females to care for
the young while others hunt and bring back food (e.g. lions, wild dogs,
meercats).  Humans do this today.  It is also common for female animals to
nurse the babies of other females in the group when they are away (lions).
Some human mothers do this today; there is no reason to believe it was not
done in the past.

"This would have created a selection pressure to wean infants earlier and
earlier, since those no longer dependent on breast milk would have been
more likely to survive their mother's death, says Kennedy."

-- Pressure from whom?  Partial breastfeeding is not equivalent to
exclusing breastfeeding.  For a child who is eating other foods, losing his
mother's breast milk would not make as much nutritional impact and it would
for an infant.
A human baby/child dependent on breast milk whose mother died would likely
have been nursed by a female relative, just as they are in some societies
today.
Babies who are weaned later have higher survival rate and therefore greater
chance of passing on their genes, selecting for later weaning ages.
It would take a very high maternal mortality rate without adoptive nursing
to select for infants who could survive without breast milk.


"What is more, the nutritional benefit of eating meat at a younger age
would have helped children's brains to grow and develop more quickly. Human
brains grow three times quicker than those of chimpanzees."

- Eating meat does not mean a child could not continue to breastfeed.
Breast milk has optimal nutrition for brain development.  When meat is not
a guaranteed source of food (and hunters might often come back empty-
handed), breast milk would assure needed nutrition for the younger members
of the group.


"But Barry Bogin of the University of Michigan at Dearborn, US, has a
different rationale for early weaning. He believes it allowed hominid
mothers to have more offspring. "By weaning at 30 months, we have a great
reproductive jump over our closest cousins; we can crank out two babies in
the time it takes a chimpanzee to have one," he says."

-- Higher birth rates does not necessarily mean higher survival rates.
Lactation amenorrhea is a survival factor for infants in primitive
societies.


Journal reference: Journal of Human Evolution (DOI:
10.1016/j.jhevol.2004.09.005)


-- I dislike seeing hypotheses presented as fact without any way of proving
them.

-Claire Bloodgood, IBCLC

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