Genomic data support the hominoid slowdown and an Early Oligocene estimate for the hominoid–cercopithecoid divergence
Bibliographic record
Abstract
Several lines of indirect evidence suggest that hominoids (apes and humans) and cercopithecoids (Old World monkeys) diverged around 23-25 Mya. Importantly, although this range of dates has been used as both an initial assumption and as a confirmation of results in many molecular-clock analyses, it has not been critically assessed on its own merits. In this article we test the robusticity of the 23- to 25-Mya estimate with approximately 150,000 base pairs of orthologous DNA sequence data from two cercopithecoids and two hominoids by using quartet analysis. This method is an improvement over other estimates of the hominoid-cercopithecoid divergence because it incorporates two calibration points, one each within cercopithecoids and hominoids, and tests for a statistically appropriate model of molecular evolution. Most comparisons reject rate constancy in favor of a model incorporating two rates of evolution, supporting the "hominoid slowdown" hypothesis. By using this model of molecular evolution, the hominoid-cercopithecoid divergence is estimated to range from 29.2 to 34.5 Mya, significantly older than most previous analyses. Hominoid-cercopithecoid divergence dates of 23-25 Mya fall outside of the confidence intervals estimated, suggesting that as much as one-third of ape evolution has not been paleontologically sampled. Identifying stem cercopithecoids or hominoids from this period will be difficult because derived features that define crown catarrhines need not be present in early members of these lineages. More sites that sample primate habitats from the Oligocene of Africa are needed to better understand early ape and Old World monkey evolution.
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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 | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".