Free The Dangerous Passion: Why Jealousy Is as Necessary as Love and Sex by David M. Buss

devote their lives to studying the
mysteries of the human mind focus on a single topic or phenomenon. Among the
ranks of psychologists we find expert specialists in areas such as aggression,
cooperation, attitudes, status, love, language, the ear, the eye, panic
disorder, attention deficit disorder, and narcissistic personality disorder.
The human mind, however, does not exist in isolated bundles. It contains a
complex web of interconnected mechanisms. Furthermore, human minds cannot be
understood individually or in isolation. Our minds are designed to deal with
the minds of other humans.
    One of the most important tools for understanding jealousy is
the theory of co-evolution—the reciprocal changes that occur sequentially in
interacting species or between the sexes within one species. Predators and prey
provide the clearest illustration of the theory of co-evolution. Rabbits are
natural prey for foxes, but the two species coexist in a special way. The rabbits
captured and eaten by foxes tend to be those who are slower, more preoccupied,
less observant, and less attentive to the hostile forces around them. The
quicker, more attentive rabbits survive and leave more descendants. Each
generation of rabbits, therefore, is slightly more adept at evading foxes than
the previous generation.
    Now consider things from the foxes’ perspective. In each
generation, foxes who are more agile and fleet of foot are more successful at
catching rabbits. The uncoordinated and sluggish foxes fail to feed and leave
fewer descendants. So each generation of foxes is in some slight way better
equipped to catch rabbits. Each increment in the speed and agility of rabbits,
in essence, imposes selection pressure on foxes, just as each increment in the
speed and agility of foxes imposes selection pressure on rabbits. The changes
over time in rabbits and foxes, like all predators and prey, are best described
as a co-evolutionary spiral that continues indefinitely, or until natural
physical limits are reached.
    The same logic applies to parasites and their hosts. Humans play
host to thousands of parasites that cannot exist without us. Parasites, as a
general rule, feed on the host organism, and can destroy it over time. Hosts
have evolved defense mechanisms to combat parasites, such as immune systems.
The parasites that survive, however, are those that are most skilled at evading
the host’s defense mechanisms. Parasites and hosts thus co-evolve in a
never-ending spiral, with each change in hosts imposing selection pressure on
parasites, and each change in parasites imposing selection pressure on the
hosts.
    The logic of reciprocal changes in interacting species applies
with equal force to interacting sexes within a species. Consider as an example the
co-evolutionary spiral that occurs between men and women over the linked issues
of commitment and sex. As I documented in
The Evolution of Desire,
women have evolved a preference for partners who show reliable indications of
the ability and willingness to channel resources to them and their children.
Over human evolutionary history, women who succeeded in attracting committed
men survived and reproduced more successfully than women who failed to attract
such men.
    Women’s preferences, in turn, can exert co-evolutionary
selection pressure on men. Men who display reliable cues to commitment are
preferentially chosen by women; men unable to display these cues get banished
from mating. Decisions to mate, however, are always made in a shroud of
uncertainty, which opens the door to deception. Some men may develop a strategy
of providing false cues to commitment, luring the woman into a sexual
encounter, and then abandoning her. Men’s deceptive strategy is one co-evolved
outcome of women’s initial preference for commitment.
    As a strategy of deception spreads, however, it produces
selection pressure on women to screen out the deceivers. Women might begin to
insist on a longer period of courtship, for