Table 2.

The relationship between brain volume, socioecology, observational measures of cognition, and performance on the cognitive tasks

Data sourceExplanatory variableDependent measuretdfPr2λ
All speciesAbsolute brain volumeCylinder4.7930<0.010.430.00
Absolute brain volumeA-not-B1.03250.160.040.69
Absolute brain volumeA-not-B (no elephant)5.4424<0.010.550.00
Absolute brain volumeComposite5.6721<0.010.600.00
Residual brain volumeCylinder2.31300.010.150.98
Residual brain volumeA-not-B0.05250.96<0.010.72
Residual brain volumeA-not-B (no elephant)0.33240.37<0.010.58
Residual brain volumeComposite0.78210.220.030.67
NonprimatesAbsolute brain volumeCylinder3.3010<0.010.520.00
Absolute brain volumeA-not-B−0.5970.710.050.00
Absolute brain volumeComposite2.5460.020.520.00
Residual brain volumeCylinder1.12100.140.110.69
Residual brain volumeA-not-B−1.8370.950.320.00
Residual brain volumeComposite−0.5860.710.050.25
PrimatesAbsolute brain volumeCylinder5.0118<0.010.580.00
Absolute brain volumeA-not-B4.3916<0.010.550.00
Absolute brain volumeComposite5.2713<0.010.680.00
Residual brain volumeCylinder2.26180.020.220.93
Residual brain volumeA-not-B2.64160.010.300.00
Residual brain volumeComposite1.69130.060.180.60
PrimatesPopulation group sizeComposite−0.75130.770.040.83
Foraging group sizeComposite−0.33130.630.010.82
Percent fruit in dietComposite0.11130.46<0.010.85
Dietary breadthComposite4.9912<0.010.680.69
Social learningComposite2.6390.030.440.00
Extractive foragingComposite3.1090.010.520.00
Tool useComposite3.1290.010.520.00
Tactical deceptionComposite4.069<0.010.650.00
PCA 1Composite3.619<0.010.590.00
  • The sign of the t statistic indicates the direction of the relationship between variables. Data regarding social learning, innovation, extractive foraging, tool use, tactical deception (all of which covary), and primate gs scores were adjusted for research effort and obtained from Reader et al. (92) and Byrne and Corp (124). PCA 1 is equivalent to the gs score calculated by Reader et al. (92) restricted to species in this dataset. We used the arcsine square-root transformed mean proportion of correct responses for each species as the dependent measure in all analyses, as this best met the statistical assumptions of our tests. Socioecological data were log transformed (group size) or arcsine square root transformed (proportion fruit in diet) for analysis.