Re: An alternative to ST and AAT

John Waters (jdwaters@dircon.co.uk)
24 Nov 1996 22:52:28 GMT

Rohinton Collins <rohinton@collins.prestel.co.uk> wrote in
article <01bbd8a2$818fb100$LocalHost@dan-pc>...
> John Waters <jdwaters@dircon.co.uk> wrote in article
> <01bbd6cb$5dfa23c0$1b2470c2@default>...
>
> The jaw would have little bearing on the size of the
pelvic outlet. In all
> hominoid species (including extinct taxa) the size of the
newborn's jaw is
> tiny in relation to the cranium, in comparison with that
of an adult skull.

JW: I don't disagree. But even allowing for the
foreshortening effect of infancy, isn't the case that
Chimpanzee newborns have slightly protrudent jaws as
compared with human babies. The effects may be small, but
they could mean the difference between a stillborn baby and
a successful birth.
>
> I'm not sure whether you understood me here John. To
quote my previous
> post:
>
> ## In apes, who have precocial young, brain growth
proceeds rapidly until
> birth,
> whereupon a slower phase ensues for about a year. In
humans, the prenatal
> phase of rapid brain growth continues until well after
birth, a pattern
> that is seen in all altricial species. This rapid
postnatal phase continues
> for a further 12 months. The effect is to give humans the
equivalent of a
> 21 month gestation period (9 months in-utero, 12 months
outside). This
> occurs because of the size limitation of the pelvic
outlet. One important
> consequence of this is that human infants are far more
helpless and for a
> much longer time than the young of the great apes. ##
>
> Clear now?

JW: I don't want to labour the point, but are you saying
that ape babies are precocial at birth? I'm not talking
about physiology here, rather behaviour.
>
> > In your last but one sentance, you use the phrase _
> > presumably with the
> > concomitant impact on social organisation._ Would you
care
> > to expand on that please?
>
> No problem John. A newborn ape can look after itself to a
certain extent
> shortly after birth. Of course it needs its mother for
food, warmth and
> protection, but it can move around by itself and begin to
feed itself
> within weeks (? any refs) of birth. This determines the
kind of social
> organisations we see in extant apes. Human newborns are
totally helpless,
> they rely on their parents for everything, including
getting from one place
> to another (at least until they can crawl) for many
months, and it is years
> before they can feed themselves. Such intensive care for
a newborn human
> requires a very different social organisation. So a
hominid species whose
> newborns were altricial as opposed to precocial (as seen
in its ancestral
> species), would be expected to adopt a different social
organisation than
> its ancestral species.

JW: This is very interesting, Roh. It seems to me to imply
that the development of altricial young would involve more
than maternal adaptations to the needs of those infants.
You use the term *social*. Would you care to speculate on
the sort of changes this might have involved?
>
> Since ape newborns are precocious, and human newborns
altricial, the latter
> being due to postnatal brain growth continuing at the
prenatal rate,
> reaching the ape newborn stage at about 1 year, I would
expect intermediate
> species (assuming the LCA to have an ape brain growth
pattern -
> parsimonious) to have a varying length in the postnatal,
fast-growth phase,
> ranging from a few weeks to 1 year (the present human
condition). This
> would be reflected in the way in which the young are
reared, and whether a
> long-term intensive care strategy would be required, as
is for human young.
> Hominids certainly did not make nests in trees.

JW: So do you think they built underground burrows, like
badgers or foxes? And would they leave their young alone in
a burrow while the mother went foraging? Or do you think
they carried their young with them wherever they went? Ape
nursing females are pretty possessive about their very
young infants. It is difficult to imagine a hominid female
being less possessive.

Another seemingly irrelevant question, Roh. Do you think
the hominid mothers put their altricial infants on the
ground every so often? They surely must have done. And if
so, do you think they laid them face downwards? Or on their
sides? Or on their backs?

If early australopithecine
> species had precocious young, because of their bipedal
adaptations they
> would not be able to grip branches (or their mum) with
their feet, a
> pre-requisite for arboreal-nesting primate.

JW: That is an interesting point, Roh. Are you suggesting
they would sleep on the ground? Barbary Apes sleep in rocky
crevices, which presumably affords some protection against
nocturnal predation. Do you think the hominids would have
moved to a higher altitude as a result of bipedalism? I
gather most of the fossils are found on elevated sites.

This would also be dependent
> upon life history patterns - were they nomadic or did
they have home bases?
> If the latter is true, how long did they stay in one
place? Long enough for
> a newborn to grow beyond its 'helpless' stage?

JW: IMO, I doubt if the helpless stage was more than a few
hours when the change of infantile development first took
place. If each extension of helplessness was only a few
hours, the nursing female could surely adapt to such a
small increase. No female could possibly know how long the
helplessness stage would last, so it would be difficult to
justify the building of a burrow etc.
>
> It is an irrelevant assumption. Anyway, punctuated
equilibrium is more
> important given a reasonably sized gene pool. The fossil
record may show
> some increase in adult brain size during the lifetime of
a species, but we
> only see a marked and definite increase after a
speciation event.

JW: I take it you are talking about all species of animals
here. In the case of hominids, the lack of a complete
fossil record could disguise a Darwinian continuum. I am
not saying that punctuated equilibrium is not appropriate
here, but I cannot help feeling that an enormous and sudden
increase in altriciality would cause grave problems for the
nursing female.
>
> > Your exposition implies a relationship between
alfricial
> > development and brain size, as far as the hominids are
> > concerned. Is this a fair interpretation?
>
> Yes. There is a physical limit - the size of the pelvic
outlet - which
> restricts the size of a newborn hominid's brain.
Obviously the
> biomechanical cost of further enlarging the pelvic outlet
(in any altricial
> hominid species) evolutionarily outweighed (and
outweighs) the cost of
> having 'helpless' young.

JW: This is my view also. Any increase in brain size would
lead to an increase in the period of helplessness after
birth. However, the increase in brain size afforded a
sufficiently increased evolutionary advantage to more than
compensate for the disadvantage of increased infantile
helplessness. It is fair to say that not everybody agrees
with this.
>
> > Jane Goodalls studies in Gombe show that the daily
travel
> > range is relatively small, particularly for females.
> > However, in more arid regions such as Senegal, the
daily
> > range ** can ** be much greater.
>
> This doesn't help your argument John. All this tells us
is that chimpanzees
> are elastic - as you would expect from a higher primate -
when it comes to
> foraging patterns and new environments.

JW: Actually, I am not concerned with the distance
travelled. As you imply, this need be no greater in a large
habitat than a small one. My interest is in the elevation
climbed by a hominid species.

Oh and be careful, that 'can' makes
> you sound like a statistician ;-) (If you aren't aware,
statisticians are
> famous for making data 'fit' their arguments, even if
just by the
> application of one three letter word - 'can')

JW: Yes indeed. How does the phrase go? Lies, damned lies
and ...
>
> When did we stop talking about newborns and babies and
start talking about
> older infants? How is this relevant to our arguments? To
whom are you
> referring when you talk about '... to carry infants on
their hips'?
> Australopithecines? Apes? Modern humans? How is this
relevant to our
> arguments?

JW: I don't know. I was not talking about Apes. Were you?
The Australopithicenes are interesting, because of the
bipedal aspect. Some people have argued that it would be
impossible for an australopithicene to carry a three year
old infant. Apes can carry such infants on their back. You
have talked of hominids carrying such infants on their
backs, piggyback fashion.

But would they really do this? After all, if you trip,
there is not likely to be enough time to prevent a nasty
fall. Traversing rough country and carrying a tired infant,
it might have been safer for an australopithicine like Lucy
to have carried the infant on one hip, holding a staff with
the other hand.

I find the whole business immensely intriguing. As you may
know, old style rucksacks were carried mainly on the
shoulders; whereas the modern style of pack transfers the
weight to the hips. This implies either a good marketing
gimmick, or that it is more efficient to transfer the
weight to the hips. The whole business of hominid
bipedalism needs much more research, particularly in
respect of the mother/infant dyad.
>
> Given the above, it is reasonable to remark that
hominids, and modern
> humans in particular, have a RELATIVELY over-developed
brain in comparison
> to the apes, being contemporaneous taxa.

JW: Yes, this was the point of my remark. You could say
that it is overdeveloped if you consider that the habitat
of the hominids and apes for most of their history has been
virtually the same. Same trees, same plants, same fruit,
same nuts, same sort of climate, same predators etc., etc.
If brains are considered to be an adaptation to habitat
requirements, or niche requirements, why are human brains
so much larger than those of apes.

The standard argument is that it was an adaptation to the
manufacture and use of tools. And yet this raises chicken
and egg types of questions. There are other more obvious
differences which may have preceded tool development,
namely bipedalism and altricial infants. Could an
adaptation to these have led to a larger brain, which then
allowed the species to develop better tools?

A final statement for the record, Roh. Some people may
think you have been a bit stingy with your references.
However, I can assure everybody that this is a very ill
researched area. There are virtually no books, or papers on
the effects of altricial development in hominids. It is
pioneering stuff, and I certainly appreciate all the
problems which you are facing in researching the answers.

Thank you once again.

John.