Who Needs Emotions? The Brain Meets the Robot

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benefits that also presented vulnerabilities. For example, genes related to the
DA system that may have enhanced novelty seeking may have provided
advantages in seeking and finding new habitats and resources. In ancestral
environments, such genetic quirks would be beneficial or at the very least
not deleterious; however, in modern environments, with availability of pure
drugs such as cocaine, disproportionate susceptibility among individuals may
occur. Gerald and Higley (2002) have proposed a fascinating model for genetic
susceptibility to alcohol dependence in relation to variations in serotonin
function. Their research shows that monkeys with lower levels of brain
5-HT tend to be less affiliative and social, to be more aggressive and impulsive,
and to have a higher mortality in the wild. These monkeys drink excessive
amounts of alcohol compared to monkeys with high 5-HT levels. Thus,
heritable traits that may have been advantageous in certain contexts could
contribute to susceptibility to alcoholism and excessive alcohol intake.
Ultimately, it is critical to address the remarkable similarities between
plant alkaloids and nervous system chemicals and receptors in animals. Figure
3.8 shows examples of cannabinoid and opiate receptors in the mammalian
brain. Sullivan and Hagen (2002) ponder this question and propose
that psychotropic substance seeking is an adaptation reflective of a coevolutionary
relationship between psychotropic plant substances and humans that
is millions of years old. Plants containing allelochemicals (toxic metabolites
used by plants to discourage herbivores and pathogens) were widespread in
the ancestral environment, and these alkaloids were often chemical analogues
of vertebrate and invertebrate neurotransmitters.
this “deep time” relationship is self-evident both in the extant
chemical–ecological adaptations that have evolved in mammals to
metabolize psychotropic plant substances and in the structure of
plant defensive chemicals that have evolved to mimic the structure,
and interfere with the function, of mammalian neurotransmitters.
(Sullivan & Hagen, 2002)
Taking an anthropological point of view, these authors suggest that extensive
evidence of substance use in antiquity may have been a mundane,
ubiquitous activity similar to how we use caffeine in the present. These authors
propose that there may have been selective and relatively specific benefits
of plant use, particularly before the advent of agriculture. The use of the
coca plant can be traced at least as far back as 7000 years ago, and Sullivan and
Hagen (2002) cite archeological evidence that the betel nut (containing
arecoline, a muscarinic agonist) was chewed 13,000 years ago in Timor and
10,700 years ago in Thailand. These authors suggest that in a foraging environment
humans may have exploited these neurotransmitter analogue chemicals
to enhance energy and fitness, particularly for nutritionally constrained