Parallel Adaptations to High Temperatures in the Archaean Eon
Bibliographic record
Abstract
LUCA blows hot and cold There is a fascination about the quest to learn more about 'LUCA', the hypothetical last universal common ancestor from which all current living organisms are descended. Fossil evidence from the time, 3.5 to 3.8 billion years ago, is sparse and so LUCA hunters rely on indirect evidence for information on LUCA's biology and environment. Reconstructions of ancestral protein sequences based on genetic evidence from extant genomes pointed to a hot environment, and a thermophilic LUCA. But ribosomal RNA sequences were thought consistent with a cooler environment. A new 'molecular thermometer' method may have resolved this apparent discrepancy. The analysis of rRNA and protein sequences from hundreds of modern species using the latest mathematical models of molecular evolution suggests that there were two phases of environmental temperature change. What was to become LUCA was first mesophilic, living in waters at about 60°C, then adapted to higher temperatures, above 70°C, to produce a thermophilic common ancestor. As the oceans then cooled the Bacteria and Archaea–Eukaryota diversified.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".