Re: Bipedalism and theorizing... was Re: Morgan and creationists

Paul Crowley (
Sun, 06 Oct 96 08:05:15 GMT

In article <01bbaf85$3724f260$> "John Waters" writes:

> Paul Crowley <> wrote in article
> >
> > I glad you appreciate the drastic nature of the behaviour
> > (although you've overstated it by putting in "new-born" and
> > apparently assuming that the infant was left alone).
> JW: I'm sorry Paul, I missed the earlier correspondance. Could
> you summarise it for me so that I may know the age of the infant and
> its guardians?

The change from the standard primate pattern of infant care to
something close to the modern Hss pattern would have happened early
in hominid evolution and could have taken about 100 Kyr to complete.
So I'm saying that since about 5mya hominid mothers have been putting
their infants down. This behaviour was a necessary precursor to
bipedalism as the proto-hominid female with a two- or three-year old
infant simply would not have been able to walk upright.

How exactly it happened is anyone's guess. Mine is that a small
population of quadrupedal apes adopted a lifestyle something like
that of the crab-eating macaque, but began living away from readily
climable trees, possibly on sandbanks or rock shelving, in an area
that was usually humid and overcast. Palm and date trees may have
provided shade. The carrying of infants in the ventral position
became impossible, probably because the females spent a certain
amount of time wading or swimming. So some sharing pattern of
infant care had to be adopted, with infants being put down for
periods when the mother needed to forage or travel in deeper water.
This behaviour required a fair degree of co-operation between
females. It also encouraged language. I feel that that type of
behaviour is still apparent from the way Hss women talk and work
together, as compared with that of Hss men

> > for a long time (several million years) hominid mothers have not
> > been carrying infants close to their bodies, as all their primate
> > ancestors did, and all their primate relatives still do.
> JW: I'm not sure I fully understand this sentence. Do mean that
> hominid mothers carried their infants with outstretched arms?

All other primate mothers carry their infants close to their
bodies _all_the_time_ -- until the infant begins to develop
independent mobility. Hss mothers don't do this. That's all
I'm saying here.

> > > JW: An extension of the period of helplessness would not
> > > come about simply through infantile inactivity.
> >
> > Why not? The more active infants would eliminate themselves and
> > leave no descendants. There's no mechanism more effective than
> > that.
> JW: The infantile helplessness of a human baby is not due to
> laziness. It is because the part of the baby's brain which controls its
> limbs is not developed at birth. Prolonged inactivity would simply lead to
> the degeneration of the nerves, leaving the infant totally
> incapacitated

My point is that *in_evolutionary_terms* infantile helplessness
does not come from lack of brain development. It's the other way
around: slowness in the development of limb muscle control comes
from the need for the infant to be immobile. Any mother will tell
you that a fully mobile six-month-old would be a nightmare. Fully
mobile two-year olds are bad enough. This is a unique situation in
the primate world. I'm saying that it's been exactly the same for
all hominids for the past 5 Myr or so. It goes with bipedalism.

The niche disallowed the standard primate method for infant care.
The next best solution involved having a largely immobile infant.
This necessitated fixed home bases and shared caring. We know we
acquired all these at some time. It's parsimonious to say it was
at the speciation of the hominid clade. It encouraged language,
the acquisition of personal property and tools and it facilitated
brain growth in infancy.