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Title: Estimating sexual size dimorphism in fossil species from posterior probability densities
Authors: Sasaki, Tomohiko
Semaw, Sileshi
Rogers, Michael J.
Simpson, Scott W.
Beyene, Yonas
Asfaw, Berhane
White, Tim D.
Suwa, Gen
Keywords: Sexual dimorphism;Fossils;Bayesian estimate;Mixture analysis;Human evolution
Issue Date: Nov-2021
Publisher: National Academy of Sciences
Citation: PNAS, 2021, 118 (44), e2113943118
Abstract: Accurate characterization of sexual dimorphism is crucial in evolutionary biology because of its significance in understanding present and past adaptations involving reproductive and resource use strategies of species. However, inferring dimorphism in fossil assemblages is difficult, particularly with relatively low dimorphism. Commonly used methods of estimating dimorphism levels in fossils include the mean method, the binomial dimorphism index, and the coefficient of variation method. These methods have been reported to overestimate low levels of dimorphism, which is problematic when investigating issues such as canine size dimorphism in primates and its relation to reproductive strategies. Here, we introduce the posterior density peak (pdPeak) method that utilizes the Bayesian inference to provide posterior probability densities of dimorphism levels and within-sex variance. The highest posterior density point is termed the pdPeak. We investigated performance of the pdPeak method and made comparisons with the above-mentioned conventional methods via 1) computer-generated samples simulating a range of conditions and 2) application to canine crown-diameter datasets of extant known-sex anthropoids. Results showed that the pdPeak method is capable of unbiased estimates in a broader range of dimorphism levels than the other methods and uniquely provides reliable interval estimates. Although attention is required to its underestimation tendency when some of the distributional assumptions are violated, we demonstrate that the pdPeak method enables a more accurate dimorphism estimate at lower dimorphism levels than previously possible, which is important to illuminating human evolution.
ISSN: 0027-8424
DOI: 10.1073/pnas.2113943118
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Type: Article
Appears in Collections:Paleobiología

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