Re: Interesting Gutsick Gibbon article

On 12/7/2024 4:02 AM, jillery wrote:

<https://youtu.be/GosX5-kuWUs>
 For those who don't know, Gutsick Gibbon is the Youtube handle for a
PhD student in Biological Anthropology.  This particular video
discusses this recent paper:
 <https://www.nature.com/articles/s41586-024-08205-2>
 It got my attention for two reasons.  First, it describes a
non-destructive method for analyzing the growth patterns of fossil
teeth, using propagation phase-contrast synchrotron microtomography.
 Second, the authors used that method to compare the tooth ontogeny of
several fossil hominids and modern apes.  Using these patterns as
proxy for overall physical development, the authors concluded that
early hominids' growth patterns were more similar to modern
chimpanzees, and different fossil hominids' growth patterns evolved to
become more similar to modern humans over time.
 Finally, the authors raise the question of whether the inferred
life-history characteristics of early Homo reflect an evolutionary
change in reproduction strategies, before substantial brain expansion
and reorganization, and before a general slow-down in life history.
 Paraphrasing Gutsick Gibbon, it was early tool use three million years
ago, which altered the selective pressures for large teeth and jaws,
which in turn allowed developmental changes for extended childhood,
which preceded the large increase in brain size.
 Discuss or ignore, as you will.
 

This is the paper that I posted before, and asked what could be determined from a sample size of one?  This paper had enough samples from chimps and humans to have error bar estimates on their develompental trajectories, but they only had 4 orangutan measurments and one of them fell squarely (right on the line) on the human trajectory.  The error bars clearly separated the trajectories of chimp and human tooth development, but they didn't have enough orangutan samples and only had the one ancient homo sample.  From their own orangutan sample, what could they infer from a single early Homo sample?
Human babies are born with larger brains to body weight than the apes and at a less physically developed state.  They are pretty helpless, and cultural changes would have had to occur in order to care for this type of infant.  Both human and ape brains have to grow with the growing infant, but the ape brains do not grow as much, and are more developed when the infant is born.  Human infant brains may be larger, but they are less developed, and the physical abilities of the infants body are also retarded compared to apes.  Before the current way that we grow larger brains evolved there must have been a stage where our brains evolved to be able to more effectively assimilate (learn) existing culture of the group, and develop cultural novelties in order to adapt to the biological changes that would be needed to go to the next level of brain development.
One way to develop better brains is to allow them to grow longer after birth.  You would just be adding to how developed the brain already is in apes at birth.  This would likely lengthen child development, but would also allow more time for the infants to learn the culture of the group as their brains developed.  The paper notes that Homo brains 1.7 million years ago were not that much larger than ape brains. Australopithecines had larger brains by body weight than chimps, and the Taung child is thought to be a little over 3 years of age when it died and it already had a brain about the size of adult chimp.  The brain might have needed to grow a bit more to have an Australopithecine adult brain size.
Ron Okimoto