Origin of human bipedalism: The knuckle-walking hypothesis revisited
Bibliographic record
Abstract
Some of the most long-standing questions in paleoanthropology concern how and why human bipedalism evolved. Over the last century, many hypotheses have been offered on the mode of locomotion from which bipedalism originated. Candidate ancestral adaptations include monkey-like arboreal or terrestrial quadrupedalism, gibbon- or orangutan-like (or other forms of) climbing and suspension, and knuckle-walking. This paper reviews the history of these hypotheses, outlines their predictions, and assesses them in light of current phylogenetic, comparative anatomical, and fossil evidence. The functional significance of characteristics of the shoulder and arm, elbow, wrist, and hand shared by African apes and humans, including their fossil relatives, most strongly supports the knuckle-walking hypothesis, which reconstructs the ancestor as being adapted to knuckle-walking and arboreal climbing. Future fossil discoveries, and a clear understanding of anthropoid locomotor anatomy, are required to ultimately test these hypotheses. If knuckle-walking was an important component of the behavioral repertoire of the prebipedal human ancestor, then we can reject scenarios on the origin of bipedalism that rely on a strictly arboreal ancestor. Moreover, paleoenvironmental data associated with the earliest hominins, and their close relatives, contradict hypotheses that place the agents of selection for bipedality in open savanna habitats. Existing hypotheses must explain why bipedalism would evolve from an ancestor that was already partly terrestrial. Many food acquisition and carrying hypotheses remain tenable in light of current evidence.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.008 |
| Scholarly communication | 0.002 | 0.004 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".