DOI: 10.5061/dryad.280gb5mx0
title: Data from: New estimates indicate that males are not larger than females in most mammal species

description: Sexual size dimorphism has motivated a large body of research on mammalian
 mating strategies and sexual selection. Despite some contrary evidence,
 the narrative that larger males are the norm in mammals – upheld since
 Darwin’s Descent of Man – still dominates today, supported by
 meta-analyses that use coarse measures of dimorphism and taxonomically
 biased sampling. With newly available datasets and primary sources
 reporting sex-segregated means and variances in adult body mass, we
 estimated statistically determined rates of sexual size dimorphism in
 mammals, sampling taxa by their species richness at the family level. Our
 analyses of wild, non-provisioned populations representing &gt;400
 species indicate that although males tend to be larger than females when
 dimorphism occurs, males are not larger in most mammal species, suggesting
 a need to revisit other assumptions in sexual selection research.
description: These data on sex-segregated body mass means and variances were
 collected from the literature, including existing published datasets and
 from primary sources. We sampled mammalian families according to their
 species richness (including the orders and families comprising at least 10
 species). We excluded data from sexually immature, captive-bred or
 food-provisioned, or pregnant individuals when these data were
 distinguished or when it was indicated that they were mixed into the data
 (see Methods section in manuscript for the few exceptions). Estimates from
 museum specimens were generally not used as we wished to make
 within-population comparisons between the sexes, and domesticated species
 were excluded apart from semi-domesticated free-ranging reindeer
 (<em>Rangifer tarandus</em>). Whenever sex-segregated means
 and variances for body length were presented alongside body mass data in a
 study included in the dataset, these data were also harvested. Prior to
 analyses, we filtered the full dataset (attached here) by sample size such
 that a minimum of 9 males and 9 females were required for inclusion, based
 on an analysis of the relationship between sample size and 95% confidence
 intervals for mean body mass (see R code), and removed rows for any
 duplicated species, keeping only the row with the highest combined (male +
 female) sample size for each unique species (subspecies were treated as
 different populations of the same species). Analyses were performed in
 RStudio (version 4.3.2) and the code used for analyses and data
 visualization are also appended here.
description: # New estimates indicate that males are not larger than females in most
 mammal species These files
 include the R code and raw data used for all analyses and data
 visualizations in the associated manuscript: Tombak KJ, Hex SBSW,
 Rubenstein DI. 2024. New estimates indicate that males are not larger than
 females in most mammal species. Nature Communications. ## Description of
 the data and file structure FILE LIST: SSD_Paper_Code.R: R code used for
 analyses and generating figures in the manuscript and supplementary
 materials. Tombak_etal_SSDinMammals_FullDataSet.csv: the full set of raw
 data used for analyses and data visualizations.
 Tombak_etal_SSDinMammals_FullDataSet.ods: the same as above, in ods
 format. Num_Spp_perFamily.csv: data on the number of species per family in
 each mammalian order with at least ten species, as well as the families of
 the order Pilosa sampled in our study. These data are from Burgin et al.
 2018 (full citation below). Num_Spp_perFamily.ods: the same as above, in
 ods format. Num_Spp_perOrder.csv: data on the number of species in each
 mammalian order with at least ten species. These data are from Burgin et
 al. 2018. Num_Spp_perOrder.ods: the same as above, in ods format.
 DATA-SPECIFIC INFORMATION FOR: Tombak_etal_SSDinMammals_FullDataSet.csv
 and Tombak_etal_SSDinMammals_FullDataSet.ods 1\. Number of variables: 18
 2\. Number of cases/rows: 666 3\. Variable List: Order: Mammalian order
 Family: Mammalian family Species: Common name of mammalian species
 Scientific_Name: Latin name of mammalian species massM: mean body mass, in
 grams, for adult males reported in the data source SDmassM: standard
 deviation of the body mass for adult males reported in the data source
 massF: mean body mass, in grams, for adult females reported in the data
 source SDmassF: standard deviation of the body mass for adult females
 reported in the data source lengthM: mean body length, in cm, for adult
 males if reported in the data source SDlengthM: standard deviation of the
 body length for adult males if reported in the data source lengthF: mean
 body length, in cm, for adult females if reported in the data source
 SDlengthF: standard deviation of the body length for adult females if
 reported in the data source n_M: sample size (number of individuals
 measured) corresponding to the mean body mass reported for adult males in
 the data source n_F: sample size (number of individuals measured)
 corresponding to the mean body mass reported for adult females in the data
 source n_Mlength: sample size (number of individuals measured)
 corresponding to the mean body length, if reported, for adult males in the
 data source n_Flength: sample size (number of individuals measured)
 corresponding to the mean body length, if reported, for adult females in
 the data source Comments: notes on the data, individuals sampled,
 exclusions/inclusions, or how the data reported from the original source
 were used to calculate the measures needed in our study Missing data code:
 NA Source: data source DATA-SPECIFIC INFORMATION FOR:
 Num_Spp_perFamily.csv and Num_Spp_perFamily.ods 1\. Number of variables: 4
 2\. Number of cases/rows: 81 3\. Variable List: Order: Mammalian order
 Family: Mammalian family Num_Spp: The number of extant species in the
 family (from Burgin et al. 2018) FivePercent_Spp: Five percent of the
 number of extant species in the family DATA-SPECIFIC INFORMATION FOR:
 Num_Spp_perOrder.csv and Num_Spp_perOrder.ods 1\. Number of variables: 3
 2\. Number of cases/rows: 17 3\. Variable List: Order: Mammalian order
 Num_Spp: Number of extant species in the order (from Burgin et al. 2018)
 FivePercent_Spp: Five percent of the number of extant species in the order
 ## Sharing/Access information Data was derived from the following sources:
 * Burgin, C. J., Colella, J. P., Kahn, P. L. & Upham, N. S. How many
 species of mammals are there? *J. Mammal.***99**, 1–14 (2018). * See list
 of sources from which the body mass and body length data for each
 mammalian species sampled were derived in
 Tombak_etal_SSDinMammals_FullDataSet.csv or
 Tombak_etal_SSDinMammals_FullDataSet.ods. ## Code/Software All analyses
 and data visualizations were generated in RStudio version 4.3.2. The R
 packages used were ggplot2, gridExtra, dplyr, tidyr, viridis, KneeArrower,
 and see. Microsoft Powerpoint was used for final compilation of some of
 the figures (described in the R code attached).