Table 1.

Results of reanalysis of a limited data set consisting solely of field reports where no human intervention was indicated

Independent variable	Dependent variable: reported frequency, corrected for research effort
	Innovation	Social learning	Tool use
Executive brain	<0.005	<0.0001	<0.001
ratio	>0.1	<0.01	>0.1
Innovation	—	<0.0001 (<0.0001)	<0.0001 (<0.0001)
frequency		<0.0001 (<0.0001)	<0.0001 (<0.0001)
Tool use	—	<0.0001 (<0.0001)	—
frequency		<0.0001 (<0.0001)

Figures indicate P values. Bracketed figures in italics indicate the probability level after executive brain ratio was partialled out by using multiple regression. The top row of figures in each cell indicates across-species results, the bottom row, independent contrast results. The limited data set took only examples from the field, and excluded questionable examples, experimental manipulations, and cases where human intervention was stated or implied. All findings were unaffected by this procedure, apart from the relationships between executive brain ratio and both innovation and tool use frequencies. The tool use result probably reflects the loss of power associated with the relatively small number of species that have been observed using tools in the wild compared with tool use in captivity (45). The fact that the vast majority of the results are robust to the extremely conservative nature of the reanalysis gives us reasonable confidence that the results are not artifacts caused by the inclusion of captive studies.