Sex ratio and maternal age in a natural fertility, subsistence population: Daughters, sons, daughters
Bibliographic record
Abstract
OBJECTIVE: To evaluate putative links between birth sex ratios (BSR = male:female births) and maternal age in a traditional, agricultural, natural fertility population. Metabolic energy, social support, and the costs and benefits associated with producing sons versus daughters can affect BSR. These variables fluctuate with maternal age. Most studies evaluating links between maternal age and BSR have been based on industrialized populations, which differ importantly from traditional indigenous communities in terms of the aforementioned socio-ecological variables. MATERIALS AND METHODS: We analyze data from 108 mothers and their 603 children living in an agricultural, pronatalist, Kakchiquel Mayan community. RESULTS: A logistic regression model, including linear and quadratic maternal age terms and women-specific random effects, shows a nonmonotonic (p = .028) relationship between log BSR and maternal age. For maternal age ≤ 22, the upper bound of the 95% confidence interval (CI) for BSR is <1, suggesting a bias toward girls. The probability of birthing a son increased early during the average mother's reproductive career, peaked at age 31.3 (approximately 95% CI = 27.1, 35.5), and decreased as she approached her perimenopausal period (p = .014). DISCUSSION: No changes in mating system, population sex ratio, mortality patterns, natural disasters, social risk, or toxic exposures were observed and thus are unlikely to explain our results. At this point, age-related changes in metabolic energy, social support, and costs and benefits associated with offspring sex cannot be excluded as possible explanations. BSR can affect growth, morbidity, and mortality. Thus, our results are relevant to numerous fields, including anthropology, ecology, demography, and public health.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".