Re: LBI Broods and Social Sharing

Paul Crowley (
Sat, 12 Oct 96 20:29:50 GMT

In article <01bbb6d9$fb253a20$252570c2@default> "John Waters" writes:

> It is clear that the nursing hominid female would need an
> improved physiological condition to meet the gestation and post
> foetal demands of an LBI brood.

I don't get this. I thought the LBI (long birth interval) was the
norm, as seen in the apes with a 4-5 year gap between offspring.
Why would such an animal need "an improved physiological . ."
Maybe you meant "SBI" (short birth interval)?

> Fortunately, the hominid nursing
> female had evolved an increase in subcutaneous fat.

Why? This basic question that cries out for an answer first.
Other primates did not evolve this.

> This enabled it to meet the demands of a growing embryo and
> the previous born infant.

This is nonsense. Carrying extra fat does not enable this. It's
a costly and extraordinary exercise. The explanation is almost
certainly that the species was liable to regular, probably annual,
periods of famine. So it was dangerous for a thin female to
become pregnant -- she'd only lose the child when the hunger came
and would probably die herself from the drain on her own resources.
This mechanism enabled our female ancestors to survive hard times,
and progenerate in good ones. So we have to identify the
(tropical) niche where the contrast between the "on" season and
the "off" season were much more extreme than those that apply to
apes, or where there is some other frequent cause of famine.

> The increase in hominid female subcutaneous fat level was due to
> the extension in the period of helplessness of the hominid infant.

You have stated no connection between these two phenomena.
I doubt if one could be made.

> This increased period of helplessness required the
> hominid nursing female to carry her baby in her arms.

You have not given a reason why helplessness developed (other
than the "improved power/weight" thing which I regard as being
as meaningless as Tony Blair's effusions about home cooking, Mom,
and apple pie - more is eternally desirable). Helplessness is,
prima facie, a disastrous development. Any reason for it must
be compelling and show *immediate* and highly beneficial results.

> This encouraged and helped to maintain bipedalism as the main
> method of ground level locomotion in the hominid specie.

Try to conceive the consequences to a chimpanzee mother (or to
any primate mother) of switching her infant from the ventral
position to carrying it in her arms - all the time! She'd be
unable to run, climb, brachiate, defend herself or her child,
or walk more than a few paces; so no feeding, no avoidance of
bullying, no escaping of predators, no sleeping at night. Yet
this is what you are saying!

> However, when a baby is carried in its mother's arms, its skin
> comes into direct contact with the mother. This can result in a
> twenty percent reduction in the amount of infant skin exposed to
> the air.

As the alternative is the ventral position (often, in the early
weeks, with an additional support from the mother's hand) the
change would be in the opposite direction.

Enough for now.