there are cultural factors, as well. For example, other work by Ekman
demonstrated culture-specific “display rules” that “specify who can
show which emotion to whom and when.” Ekman concludes his com-
mentary to a beautiful “definitive edition” of Darwin’s book on emo-
tions thus:
How much we are influenced by individual experience and how much
by our evolutionary history varies, depending upon what aspect of our
behavior we are considering. It is never a question only of nature or only
of nurture. We are biosocial creatures, our minds are embodied, reflect-
ing our lives and the lives of our ancestors. Darwin led the way not only
in the biological sciences but in the social sciences as well.Darwin’s discussion of human facial expressions drew upon the work
of French neurologist Guillaume Duchenne (1806-1875), who studied
the muscular control of facial expressions by selectively activating
specific muscles using direct electrical stimulation. The zygomati-
cus muscle lifts the corners of the mouth when we smile. Duchenne
contended that spontaneous smiles—ones associated with true enjoy-
ment—also involve activation of the orbicularis oculi muscles around
the eyes (Fig. 21.2). Ekman has called this latter kind of smile—often
evoked in contexts of pleasure, joy, or enthusiasm—the Duchenne
smile, honoring Duchenne’s pioneering work.
Facial expressions are one aspect of body signatures associated
with emotions, and facial expressions appear to function primarily
to communicate emotions to others. Other body signatures include
changes in heart rate, blood pressure, and skin temperature (auto-
nomic nervous system effects); changes in tone of voice and body
posture; and changes in release of hormones into the blood circulation
(neuroendocrine effects)— such as cortisol and adrenaline from the
adrenal glands and oxytocin from the hypothalamus (via the pitu-