Dawkins (2012)

Dawkins (2017)

de Waal (1999)

Dehaene et al (2017)

Descartes (1637)

Ekman (1993)

Fanselow, Pennington (2017)

Fanselow, Pennington (2018)

Gibson et al (2015)

Griffin (1976)

Griffin (2015)

Hess (1962)

Heyes (1995)

Heyes (2008)

Heyes (2015)

Heyes (2016)

Heyes (2017)

Huxley (1954)

Izard (1990)

Keller (1973)