Bock, W. J. (1959). Preadaptation and multiple evolutionary pathways. Evolution, 13(2), 194-211.
Brunsdon, C., & Chen, H. (2014). GISTools: Some further GIS capabilities for R. R package version 0.7-4. https://CRAN.R-project.org/package=GISTools.
Butcher, G. S., & Rohwer, S. (1989). The evolution of conspicuous and distinctive coloration for communication in birds. In Current ornithology  (pp. 51-108). Springer, Boston, MA.
Butler, M.A. and King, A.A. (2004). Phylogenetic comparative analysis: a modeling approach for adaptive evolution. The American Naturalist164 (6), pp.683-695.
Cheney, D. L., & Seyfarth, R. M. (2005). Constraints and preadaptations in the earliest stages of language evolution. The Linguistic Review22 (2-4), 135-159.