Who Needs Emotions? The Brain Meets the Robot

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specificity and flexibility within these networks, appears to be conserved
in evolution. This is exemplified by examining the role of dopamine in
reward and plasticity, serotonin in aggression and depression, and opioid
peptides in pain and pleasure. Moreover, across the course of thousands
of years, humans, through interactions with plant alkyloids, have discovered
how to facilitate or blunt emotions with psychoactive drugs.
Thus, while neurochemical systems mediating emotion generally serve
a highly functional and adaptive role in behavior, they can be altered
in maladaptive ways in the case of addiction.
In attempting to understand the elements out of which mental
phenomena are compounded, it is of the greatest importance to
remember that from the protozoa to man there is nowhere a
very wide gap either in structure or in behavior.
—Bertrand Russell (The Analysis of Mind, 1921)
Emotions are necessary for the survival of the individual and the
species. Therefore, a simple answer to the title of this book is that all organisms
on earth need emotional systems, in their broadest biological definition.
Emotional systems enable animals to more effectively explore and
interact with their environment, eat, drink, mate, engage in self-protective
and defensive behaviors, and communicate. Thus, a robot designed to survive
in the world as successfully as its living counterparts undoubtedly would
require an equivalent system, one that instills urgency to its actions and
decisions—in short, one that motivates and directs. Along with exquisitely
designed perceptual, cognitive, and motor networks, evolution has enabled
built-in affective mechanisms that in essence constitute a powerful, readily
available energizer that ensures efficiency and maximizes survival. The
basic premise of this chapter is that emotions are derived from complex,
neurochemically coded systems, structured by evolution, that are present
in one form or another from single-celled bacteria to primates. Of course,
human subjective awareness of a negative emotion such as dejection or humiliation
and a crayfish displaying a submissive posture following a struggle
with a conspecific are vastly different events; yet one is struck by shared
features that characterize neurochemical coding and behavioral mechanisms
throughout the evolutionary development of affective systems. Within the
rich array of diverse molecules, proteins, neurotransmitters, receptors, and
neurohormones in living organisms—some of which have become specialized
for emotion—there is a striking phylogenetic conservation of chemical
signaling molecules, many of which have played apparently related roles