Cavalli-Sforza et al. (1994), cited after
V. Ginsburgh, S. Weber, The Palgrave Handbook of Economics and Language, Springer (2016), p. 182.
doi.org
B. M. von Holdt et al., "Whole-genome sequence analysis shows that two endemic species of North American wolf are admixtures of the coyote and gray wolf", Science Advances 27 Jul 2016: Vol. 2, no. 7, e1501714, doi:10.1126/sciadv.1501714.