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Brain size and the human cranial base: a prenatal perspective
1Evolutionary Anatomy Unit, Department of Anatomy and Developmental Biology, University College London, London WC1E 6JJ, UK. ucgansj@ucl.ac.uk
American Journal of Physical Anthropology
|July 19, 2002
Summary
This study investigated human fetal development, finding no evidence that brain size increases cause changes in cranial base flexion or petrous bone orientation during prenatal development. These findings challenge evolutionary hypotheses about skull form origins.
Area of Science:
- Human evolutionary biology
- Developmental biology
- Paleoanthropology
Background:
- The cranial base is crucial for understanding human skull evolution.
- Modern humans exhibit distinct petrous bone orientation and basicranial flexion compared to other primates.
- Previous hypotheses suggest these differences stem from increased brain size relative to cranial base length.
Purpose of the Study:
- To test evolutionary hypotheses regarding cranial base development in a prenatal context.
- To investigate the relationship between brain size and cranial base morphology during human fetal development.
Main Methods:
- Utilized high-resolution magnetic resonance imaging (hrMRI) on 46 human fetuses (10-29 weeks gestation).
- Measured basicranial flexion, petrous reorientation, cranial base lengths, and endocranial volumes.
- Performed bivariate comparisons with gestational age and statistical analyses.
Main Results:
- Observed temporal trends including coronal rotation of petrous bones and basicranial flattening.
- Found significant increases in relative endocranial sizes throughout gestation.
- Statistical analyses did not support the hypothesis that increased endocranial size drives basicranial flexion or petrous reorientation.
Conclusions:
- The study's findings do not corroborate the hypothesis that prenatal increases in relative endocranial size cause basicranial flexion and petrous reorientation.
- Evolutionary propositions linking brain size increases to these specific cranial base changes are not supported in the investigated prenatal period.