The role of homoploid hybridization in evolution: A century of studies synthesizing genetics and ecology
Bibliographic record
Abstract
While homoploid hybridization was viewed as maladaptive by zoologists, the possibility that it might play a creative role in evolution was explored and debated by botanists during the evolutionary synthesis. Owing to his synthetic work on the ecological and genetic factors influencing the occurrence and effects of hybridization, G. Ledyard Stebbins' contributions to this debate were particularly influential. We revisit Stebbins' views on the frequency of hybridization, the evolution of hybrid sterility, and the evolutionary importance of transgressive segregation, introgression, and homoploid hybrid speciation in the context of contemporary evidence. Floristic surveys indicate that ∼10% of plant species hybridize, suggesting that natural hybridization is not as ubiquitous as Stebbins argued. There is stronger support for his contention that chromosomal sterility is of greater importance in plants than in animals and that selection drives the evolution of hybrid sterility. Stebbins' assertions concerning the frequent occurrence of transgressive segregation and introgressive hybridization have been confirmed by contemporary work, but few studies directly link these phenomena to adaptive evolution or speciation. Stebbins proposed a mechanism by which chromosomal rearrangements partially isolate hybrid lineages and parental species, which spurred the development of the recombinational model of homoploid speciation. While this model has been confirmed empirically, the establishment of reproductively independent hybrid lineages is typically associated with the development of both intrinsic and extrinsic reproductive barriers. We conclude by reflecting on outcomes of hybridization not considered by Stebbins and on possible future research that may extend our understanding of the evolutionary role of hybridization beyond Stebbins' legacy.
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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 | 0.006 | 0.009 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.005 | 0.006 |
| Science and technology studies | 0.003 | 0.027 |
| Scholarly communication | 0.008 | 0.018 |
| Open science | 0.002 | 0.006 |
| Research integrity | 0.004 | 0.009 |
| 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".