It is a classically accepted view that
reduction of tooth size in hominins is linked with having a larger
brain. The reasoning is that larger brains allowed hominins to start
making stone tools and that the use of these tools reduced the need to
have such large chewing teeth.
But recent studies by other authors found
that hominins had larger brains before chewing teeth became smaller,
and they made and used stone tools when brains were still quite small,
which challenges this relationship.
‘Our brains and teeth did not evolve in lock step and were likely influenced by different ecological and behavioral factors.’
A new study from the George Washington University's Center for the
Advanced Study of Human Paleobiology (CASHP) found that whereas brain
size evolved at different rates for different species, especially during
the evolution of Homo, the genus that includes humans, chewing teeth
tended to evolve at more similar rates.
The finding suggests that our
brains and teeth did not evolve in lock step and were likely influenced
by different ecological and behavioral factors.
The new study evaluates this issue by measuring and comparing the
rates at which teeth and brains have evolved along the different
branches of the human evolutionary tree.
"The findings of the study indicate that simple causal relationships
between the evolution of brain size, tool use and tooth size are
unlikely to hold true when considering the complex scenarios of hominin
evolution and the extended time periods during which evolutionary change
has occurred," said Aida Gómez-Robles, lead author of the paper and a
postdoctoral scientist at GW's CASHP.
To conduct the research, Dr. Gómez-Robles and her colleagues
analyzed eight different hominin species. The researchers identified
fast-evolving species by comparing differences between groups with those
obtained when simulating evolution at a constant rate across all
lineages, and they found clear differences between tooth evolution and
If the classical view proposing co-evolution between
brains and teeth is correct, they expected to see a close correspondence
between species evolving at a fast rate for both traits. The
differences they observed indicate that diverse and unrelated factors
influenced the evolution of teeth and brains.
"Once something becomes conventional wisdom, in no time at all it
becomes dogma," said Bernard Wood, university professor of human origins
at GW and a co-author of the paper. "The co-evolution of brains and
teeth was on a fast-track to dogma status, but we caught it in the nick
The research is published in the Proceedings of the National Academy of Sciences