 Perhaps the fiercest critic of the concept of instinct was the Berkeley-educated Chinese psychologist Zing-Yang Kuo (Guō Rènyuǎn) who was dedicated to a Watsonian vision of psychology as an experimental science grounded on behaviorist principles (Honeycutt 2011). Kuo pejoratively referred to instinct theory as “finished psychology” because it discouraged researchers from exploring the potential influences of learning early in an organism’s life. As he explained, “[t]he preconception of instinct has often betrayed the psychologist into overlooking the new environmental factors which are chiefly responsible for the supposedly unlearned acts” (Kuo 1921, 653). In his earlier writings, Kuo (1921) admitted that certain “hereditary action units” appear early in development and could be classified as instincts, provided that they are viewed merely as developmental resources and not as functional behaviors (Honeycutt 2011). However, this admission inspired critics, such as Geiger (1922), to object that Kuo was implicitly relying on the very concept of instinct which he purported to reject. This prompted Kuo (1924; 1929) to revise his position, ultimately questioning the very distinction between heredity vs acquired traits (Honeycutt 2011). His main argument assumed that in order to identify some behavior as hereditary (as opposed to acquired), it would be necessary to identify three things: (1) some fixed behavioral pattern, (2) the neuro-physiological mechanisms generating that pattern, and (3) a link to specific germ cells responsible for producing that mechanism. Kuo maintained that there simply were no fixed behaviors, let alone ones that could be associated with definite neuromuscular patterns (Honeycutt 2011). At the same time, available embryological evidence (e.g. Carmichael 1925) revealed that germ cells do not act independently of environmental influences during development. Thus, Kuo concluded that the very idea of a hereditary trait is, ‘‘beyond any experimental approach, and will always remain as an unverifiable abstraction which serves no scientific purpose whatever’’ (Kuo 1929, 195). A true scientist, Kuo argued, would not be satisfied with labelling behavior ‘instinctive’ but would demand a causal analysis of its origin in the embryo, asking ‘How are our Instincts Acquired?’ (Kuo 1922, 344)