Comparing endocranial ontogenetic trajectories in extant great and lesser apes
Bibliographic record
Abstract
Differences in adult morphology arise as a result of modifications to ancestral developmental patterns. Studies of evolutionary changes to brain development in primates can provide important clues about the evolution of human cognition, but are hindered by the lack of preserved neural tissue in the fossil record. As brain structure is mirrored in the endocranium, we have used endocasts (virtual casts of the endocranial cavity) to capture brain shape in a geometric morphometrics analysis. Here, we compare the postnatal developmental changes of the endocasts of modern humans (n=93), chimpanzees (n=61), gorillas (n=64), orangutans (n=72) and hylobatids (n=21) to assess evolutionary changes in the tempo and mode of brain development. We tested whether ontogenetic trajectories based on Procrustes shape coordinates and centroid sizes overlapped in shape‐space and form‐space and differed in their direction. In the subspace of the first three principal components, explaining >;71% of the variance in shape‐space, our results show a conserved pattern of endocranial shape development in hominids. Hominids and hylobatids have similar ontogenetic trajectories in shape‐space, yet have distinct shapes at all stages of development. These findings indicate that differences in ontogenetic shape changes are observable from the first stage of postnatal development, suggesting that divergences from an ancestral pattern of primate development occur at an earlier prenatal stage. This research was supported by the Max Planck Society and by the Natural Sciences and Engineering Research Council of Canada (NS).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".