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Subject: 1.77-Million-Year-Old Fossil Challenges Human Big Brain Theory
Date: Sun, 1 Dec 2024 23:06:18 -0700
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https://scitechdaily.com/1-77-million-year-old-fossil-challenges-human-big-brain-theory/

Recent research challenges the theory that
long childhood in humans is due to large
brain sizes. Instead, analysis of early
Homo fossil teeth suggests that prolonged
development was necessary for enhanced
cultural learning and knowledge sharing,
which later contributed to larger brains
and extended lifespans.

Compared to the great apes, humans have
an exceptionally long childhood. During
this period, parents and other adults
contribute to their physical and cognitive
development, ensuring they acquire all the
cognitive skills necessary for thriving in
the complex social environments of human
groups.

The prevailing theory has been that the
extended growth period of modern humans
evolved as a consequence of the increase
in brain volume, which requires substantial
energy resources to grow. However, a new
study on the dental growth of an exceptional
fossil suggests the ‘big brain – long
childhood’ hypothesis may need to be revised.

The study, conducted by scientists from the
University of Zurich (Switzerland), the
European Synchrotron Radiation Facility
(ESRF, Grenoble, France), and the Georgian
National Museum (Georgia) and published in
Nature, used synchrotron imaging to study
the dental development of a near-adult
fossil of early Homo from the Dmanisi site
in Georgia, dated to around 1.77 million
years ago.

“Childhood and cognition do not fossilize,
so we have to rely on indirect information.
Teeth are ideal because they fossilize well
and produce daily rings, in the same way
that trees produce annual rings, which
record their development,” explains
Christoph Zollikofer from the University of
Zurich and the first author of the
publication.

“Dental development is strongly correlated
with the development of the rest of the
body, including brain development. Access
to the details of a fossil hominid’s dental
growth therefore provides a great deal of
information about its general growth,” adds
Paul Tafforeau, scientist at the ESRF and
co-author of the study.
....
“The results showed that this individual
died between 11 and 12 years of age, when
his wisdom teeth had already erupted, as
is the case in great apes at this age,”
explains Vincent Beyrand, co-author of the
study. However, the team found that this
fossil had a surprisingly similar tooth
maturation pattern to humans, with the
back teeth lagging behind the front teeth
for the first five years of their
development.
....
This is where the ‘big brain – long
childhood’ hypothesis is tested. Early
Homo individuals did not have much
bigger brains than great apes or
australopithecines, but they possibly
lived longer. In fact, one of the
skulls discovered at Dmanisi was that
of a very old individual with no teeth
left during its last few years of life.
“The fact that such an old individual
was able to survive without any teeth
for several years indicates that the
rest of the group took good care of
him,” comments David Lordkipadnize of
the National Museum of Georgia and
co-author of the study. The older
individuals have the greatest experience,
so their role in the community likely was
to pass on their knowledge to the younger
individuals. This three-generation
structure is a fundamental aspect of the
transmission of culture in humans.

It is well known that young children can
memorize an enormous amount of information
thanks to the plasticity of their immature
brains. However, the more information they
have to memorize, the longer it takes.

This is where the new hypothesis comes in.
Children’s growth would have slowed down at
the same time as cultural transmission
increased, making the amount of information
communicated from old to young increasingly
important. This transmission would have
enabled them to make better use of available
resources while developing more complex
behaviors and would thus have given them an
evolutionary advantage in favor of a longer
childhood (and probably a longer lifespan).

Once this mechanism was in place, natural
selection would have acted on cultural
transmission and not just on biological
traits. Then, as the amount of information
to be transmitted increased, evolution
would have favored an increase in brain
size and a delay in adulthood, allowing us
both to learn more in childhood and to have
the time to grow a larger brain despite
limited food resources.
....


https://www.nature.com/articles/s41586-024-08205-2
Dental evidence for extended growth in
early Homo from Dmanisi


Abstract
Human life history is characterized by an
extended period of immaturity during which
there is a disjunction between cerebral and
somatic growth rates. This mode of ontogeny
is thought to be essential for the
acquisition of advanced cognitive
capabilities in a socially complex
environment while the brain is still
growing. Key information about when and how
this pattern evolved can be gleaned from the
teeth of fossil hominins because dental
development informs about the pace of life
history. Here we show that the first
evolutionary steps towards an extended growth
phase occurred in the genus Homo at least
1.77 million years ago, before any substantial
increase in brain size. We used synchrotron
phase-contrast tomography to track the
microstructural development of the dentition
of a subadult early Homo individual from
Dmanisi, Georgia. The individual died at the
age of 11.4 ± 0.6 years, shortly before
reaching dental maturity. Tooth growth rates
were high, similar to rates in living great
apes. However, the Dmanisi individual showed
a human-like delayed formation of the
posterior relative to the anterior dentition,
and a late growth spurt of the dentition as a
whole. The unique combination of
great-ape-like and human-like features of
dental ontogeny suggests that early Homo had
evolved an extended growth phase before a
general slow-down in life history, possibly
related to biocultural reproduction rather
than brain growth.