Pair-Living Emerged Early in Placental Mammals
Bibliographic record
Abstract
It is widely assumed that the first placental mammals were solitary. Here, we tested this assumption and which ecological and life history factors are related to mammalian social organization. We compiled a comprehensive database by reviewing over 14,000 primary peer-reviewed publications on the social organization of the 5,390 extant placental mammal species. We found empirical data for 726 species across 1,473 populations: 353 populations were primarily solitary, 250 populations pair living, and 870 populations group living. Notably, 367 species (51%) and 583 populations (40%) exhibited intraspecific variation in social organization. Using a Bayesian phylogenetic framework that incorporates intraspecific variation, we show that the ancestral placental mammal was mainly but not exclusively solitary, displaying intraspecific variation. Pair living was estimated to account for approximately 26% of ancestral social organization. Phylogeny explained most of the variation between species, while life history and ecology were less important. Our analysis found that the ecology and life history of extant solitary and pair-living mammals is very similar and different from those of group-living mammals. Our results revise prevailing theories of mammalian social evolution, revealing that pair living emerged early, shifting the focus of studying mammalian social evolution from the origins of pair living to the origins of group living.
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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 | 0.004 |
| 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 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| 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".