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Birth spacing patterns in humans and apes
1Orangutan Research and Conservation Project, Department of Archaeology, Simon Fraser University.
American Journal of Physical Anthropology
|October 1, 1990
Summary
This study introduces a survival analysis to accurately estimate primate birth intervals, accounting for censored data and offspring mortality. Orangutans have the longest median birth interval, followed by chimpanzees, gorillas, and humans.
Area of Science:
- Primate Ecology and Behavior
- Human Evolutionary Biology
- Demography and Biostatistics
Background:
- Comparative studies of primate birth intervals face analytical challenges including right-censored data, small sample sizes, non-normal distributions, and confounding effects of early offspring mortality.
- Life history differences, such as menopause, further complicate the interpretation of birth interval dynamics across species.
Purpose of the Study:
- To apply a robust survival analysis method to minimize common problems in estimating birth intervals in wild primates and humans.
- To compare birth interval lengths across different primate species and a human population using consistent analytical techniques.
Main Methods:
- A survival analysis model was employed to address issues of data censoring, sample size, and offspring mortality.
- The analysis utilized published data for wild chimpanzees (Gombe) and gorillas (Virunga), alongside new data for wild orangutans (Tanjung Puting) and the Gainj people of Papua New Guinea.
Main Results:
- Estimated median birth intervals, excluding cases of early offspring death, were calculated for four populations.
- Orangutans exhibited the longest median birth interval (92.6 ± 2.4 months), followed by chimpanzees (66.6 ± 1.3 months), gorillas (45.5 ± 1.2 months), and the Gainj humans (43.3 ± 1.0 months).
Conclusions:
- The applied survival analysis provides a more reliable method for comparing birth intervals across species with varying life histories and data limitations.
- Significant differences in median birth intervals exist among orangutans, chimpanzees, gorillas, and humans, highlighting species-specific reproductive strategies.