Paul Vasey (1995).
441
Jean-Baptiste Leca et al. (2014).
442
Jake Brooker et al. (2021).
443
Frank Beach (1949).
444
Clellan Ford and Frank Beach (1951); Neel Burton (2015).
445
Bruce Bagemihl (1999); Alan Dixon (2010).
446
Linda Wolfe (1979); Gail Vines (1999).
447
Bruce Bagemihl (1999), p. 117.
448
Frans de Waal (1987) (1997).
449
Takayoshi Kano (1992).
450