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>From: harnad@elbereth.rutgers.edu (Stevan Harnad)
Newsgroups: comp.ai.philosophy,sci.philosophy.tech,talk.philosophy.misc,sci.psychology
Subject: What is Mood For? PSYC Call for Commentators
Keywords: evolution, adaptation, behavior, information, consciousness
Message-ID: <Nov.25.14.26.46.1991.19228@elbereth.rutgers.edu>
Date: 25 Nov 91 19:26:51 GMT
Reply-To: harnad@elbereth.rutgers.edu (Stevan Harnad)
Followup-To: sci.psychology.digest
Organization: Rutgers Univ., New Brunswick, N.J.
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The following brief Target Article has just appeared in PSYCOLOQUY
2.9.3 (also sci.psychology.digest), a refereed electronic journal of
peer discussion in the cognitive and biobehavioral sciences. Brief
formal commentaries (~200 lines max.) on this article are now invited.
Please do NOT send the commentaries to this list but to
psyc@pucc.bitnet or psyc@pucc.princeton.edu if you want them to appear
in PSYCOLOQUY with the author's Response.

Commentaries should include your full name and affiliation, an
indexable title, and a formal reference list (where appropriate). All
contributions will be refereed.

PSYCOLOQUY   ISSN 1055-0143     Sun, 24 Nov 91       Volume 2 : Issue   9.2
      (1) 2.9.2 Target Article for Commentary: What is Mood for? / Nesse

----------------------------------------------------------------------

		WHAT IS MOOD FOR? 
 
		Randolph M. Nesse 
		The University of Michigan 
		Department of Psychiatry 
		C 440 Med-Inn Bldg. 
		Ann Arbor, MI 4809-0840 
		(313) 764-5348 
		Nesse@um.cc.umich.edu 
 
ABSTRACT:  What evolutionary advantages have shaped the human capacity
for mood? Answers are suggested if moods are seen as specialized states
that increase our ability to cope with certain situations. This target
article considers the hypothesis that high mood helps individuals take
full advantage of the opportunities in propitious situations, whereas
low mood motivates them to seek help, be socially submissive, conserve
resources, and consider alternative strategies in situations where
investments are not paying off.

RATIONALE FOR SOLICITING PEER COMMENTARY: The "skywriting" format
requires paring away all but the skeleton of the argument and
unfortunately allows few citations. Nonetheless, the format is
excellent for my goal of encouraging psychiatrists, psychologists, and
evolutionists to recognize that the question, "What is mood for?" is
legitimate, important, and answerable. I would especially appreciate
comments about (1) the basic approach of seeking evolutionary
explanations for emotions in the adaptive challenges of the situations
that shaped them, (2) alternative hypotheses about the functions of
mood, and (3) the plausibility of the "propitiousness hypothesis" and
(4) additional ways in which it can be tested.

KEYWORDS: Mood, evolution, natural selection, fitness, emotion, adaptation, 
function, depression, psychology, psychiatry. 
 
What function, if any, is served by the capacity for high and low
moods? The development of new psychotropic drugs makes this question
more important, and recent advances in evolutionary approaches to
behavior make it more tractable. I shall (1) briefly justify the
attempt to understand the evolutionary functions of mood, (2) review
major proposals about the functions of mood, and (3) attempt to show
how these proposals fit within a broader hypothesis.

The trait to be explained is high and low mood, that is, ordinary
happiness and sadness. These are addressed as a single trait because
their characteristics appear to be opposite sides of the same coin, and
because their brain regulation mechanisms are closely related, as
demonstrated in manic-depressive illness. Mania, depression, and grief
are not primary objects of explanation here because it is difficult to
tell whether they are sub-specialized adaptations, exaggerations of
normal responses, or pathological states unrelated to normal mood.

It is now recognized that biological traits require evolutionary
explanations of their origins and functions as well as proximate
explanations of their mechanisms and ontogeny (Mayr, 1983). Debates
continue, however, about how to decide whether or not a trait is an
adaptation, how to specify the functions of a trait, what kinds of
evidence are admissible, how evidence should be marshalled, and the
degree of optimality shaped by natural selection (Sober, 1984). These
debates are useful, but so far there is no sign of early consensus. In
the meantime, it is essential that we continue, as best we can, to
propose and test hypotheses about specific traits.

there are several good reasons to think that the capacity for mood was
shaped by natural selection and that it therefore requires an
evolutionary explanation. First, mood is a complex, universal trait and
thus unlikely to be a product of drift, simple mutation, or any process
other than natural selection. Second, the brain mechanisms that
regulate mood could have been shaped only for a trait that was itself
an adaptation. Third, mood responds in predictable ways to specific
situations. Finally, mood consists of stable constellations of
behavioral, physiological and cognitive states that have obvious major
impact on fitness. These arguments do not prove that mood has an
evolutionary explanation, but they justify the search, especially since
the best evidence that a trait is indeed an adaptation is the discovery
of its function.

Two main functions have been proposed for mood: communication and
motivation. Mood has been thought (1) to communicate either a need for
assistance or an individual's rank in a group, and (2) to motivate and
regulate the timing and locus of effort.

Of the two communicative functions of mood, eliciting aid is the more
straightforward. The infant's cry alerts the care-giver that something
is amiss. Later, the toddler's crying signal's separation and motivates
the parent and child to stay together, as described by Bowlby and
Harlow (Bowlby,1969). In adulthood, expressions of sadness solicit aid
from relatives and friends. Many authors have noted that low mood can
also be used deceptively to manipulate others. The solicitation of aid
cannot, however, explain all aspects of mood. In particular, it cannot
readily explain the benefits of happiness, or the physiological and
cognitive changes of high and low mood. Furthermore, if the only
function of mood is communication, it is difficult to explain the
intensity of moods that are experienced alone in the middle of the
night.

Mood also communicates social rank. High mood communicates dominance, low 
mood, submissiveness, and these signals prevent useless fights that would 
only harm both combatants. John Price has long advocated this function for 
mood (Price, 1967), and support has come from others (Gardner, 1982). In 
vervet monkeys, lowered status decreases activity in serotonergic brain 
mechanisms and the administration of serotonergic antidepressants can
increase dominance rank (Raleigh, McGuire, Brammer, Pollack, & Yuwiler,
1991). Low mood motivates behavior to placate dominants, while high
mood motivates high-status individuals to act in ways that maintain and
increase their position in the hierarchy. Although mood undoubtedly
serves these functions, several simple observations suggest that this
cannot be its only role: some events that profoundly influence mood do
not involve social position, some low-status people are happy, and many
high-status people are unhappy.

Mood also has motivational and regulatory functions. One function is to
adjust the timing of effort. When investments are not paying off, it is
wise to stop investing in order to conserve efforts for a later time.
The "conservation-withdrawal response" fits in this category (Engel &
Schmale, 1972), as do analogies between low mood and hibernation. Less
well appreciated are the benefits that high mood offers by increasing
investments at times of high payoff.

The other motivational function of mood is to regulate the locus of
investment. If a strategy is not paying off, or if a goal seems
unattainable, it is wise not only to conserve resources for a more
propitious time, but also to reconsider the viability of the strategy.
Emmy Gut takes this argument the farthest with her suggestion that
depression is an adaptation that motivates social withdrawal in order
to facilitate a reconsideration of how or whether to pursue receding
goals (Gut, 1989). This would explain Bibring's observation that
depression arises from the inability to give up unattainable goals
(Bibring, 1953). Behaviorists propose a similar function in describing
reactions to decreased reinforcement. The maladaptive aspects of
Seligman's helplessness-hopelessness response have been emphasized
(Seligman, 1975), but its foundations may lie in the benefits of not
wasting time and energy on futile efforts.

These four functions of mood are all correct, in part, but none is
sufficient. An explicitly evolutionary approach suggests a broad
hypothesis that integrates the functions of mood. Like other emotions,
high and low mood are behavioral subroutines, specialized states that
have been shaped to increase fitness in certain situations. An
evolutionary explanation of an emotion does not just consist of
describing its functions. Instead, the explanation must first specify
the situations in which the emotion offers advantages, and then show
how the emotion's characteristics increase fitness in the face of the
specific adaptive challenges that arise in those situations (Nesse,
1990, 1991). The characteristics of fear, for example, are useful in
situations that are dangerous. Mood is more complicated.  Because it is
a continuum from high to low, we must look, not for a single situation,
but for some varying aspect of the environment whose different levels
require different behavioral strategies. This approach follows the
behavioral ecological model of searching for the environmental cues and
cognitive mechanisms that regulate various aspects of behavior (Krebs &
Davies, 1984). A primary goal is discover what environmental variable
is tracked by mood.

The environmental variable that seems most likely to regulate mood is
the perceived propitiousness of current circumstances. In propitious
situations, small investments have a high likelihood of a large payoff.
In unpropitious situations, any amount of effort is likely to be
wasted. The propitiousness of a situation influences mood, which in
turn adjusts cognition, physiology, and behavior in coordinated ways
that increase the ability to cope effectively with the situation at
hand. Propitious situations induce high mood, which communicates high
or increasing status, motivates increased energy and risk-taking in
order to get full advantage from short-lived opportunities, and
motivates increased investment in whatever strategies are working well.
If the opportunity is social, the confidence of high mood motivates new
relationships and status challenges that are risky but that might now
pay off. Unpropitious situations induce low mood, which communicates
the need for aid and submissive social withdrawal, and motivates
conserving resources and considering other possible strategies or
goals. When a previously rewarding strategy suddenly stops paying off,
frustration induces a short burst of aggressive energy to see whether
additional effort is likely to overcome the obstacle. If not,
hopelessness may be adaptive when it leads to considering other
opportunities.

In sum, mood seems to motivate the allocation of resources away from
efforts where they will be wasted, and towards those times, strategies,
and enterprises where investments will have a large payoff. In this
sense, mood is an algorithm that shapes major life strategies by
determining how resources are allocated. Making such decisions well is
as crucial to human Darwinian fitness as it is for other animals. Most
animals must decide which prey to pursue and how long to stay in each
patch. For humans (and for other social species), resource allocation
decisions are inordinately complex, because they involve multiple
goals, many individuals and groups, and networks of potentially
incompatible strategies. Resources, for humans, are mostly social
resources. Our investments are mostly in friends, allies and groups,
and the rewards we seek are likewise mostly social. This explains why
social cues so profoundly affect mood, why social withdrawal so
regularly characterizes low mood, and why gregariousness characterizes
high mood.

In addition to providing a framework that integrates previously
proposed functions of mood, this hypothesis makes several predictions.
First, the effects of different environmental situations on mood should
be proportional to their effects on anticipated propitiousness. This
contrasts with the simpler view that moods are affected by gains and
losses and suggests the non-obvious prediction that the effects on mood
should be small when gains are not accompanied by new opportunities and
when losses involve no loss of future rewards per unit of investment.
Second, the characteristics of high and low mood should offer
advantages in situations of high and low propitiousness, respectively.
Several such functions have been mentioned, but much remains to be done
to understand how the characteristics of mood offer benefits. Third,
people who lack the capacity for mood should be at a disadvantage
compared to normal people. Those who lack the capacity for happiness
should be unable to take advantage of opportunities, while those who
lack the capacity for sadness should persist, blithely, in efforts that
offer few payoffs.

This is a bare summary of a longer paper which is in preparation. I do
not claim that the proposed hypothesis for the functions of mood is
correct, but only that it is plausible, and that it demonstrates how a
modern evolutionary approach may increase our understanding of mood. I
welcome comments, especially those about other hypothesized functions
of mood that I have not discussed, and ways in which the propitiousness
hypothesis can be clarified and tested.

REFERENCES  
 
Bibring, E. (1953). The mechanisms of depression. In P. Greenacre
(Eds.), Affective Disorders (pp. 13-48). New York: International
Universities Press.

Bowlby, J. (1969). Attachment and Loss, Vol. 1. New York, Basic Books.  
 
Engel, G., & Schmale, A. (1972). Conservation-withdrawal: A primary
regulatory process for organismic homeostasis. In R. Porter & J. Night
(Eds.), Physiology, Emotion, and Psychosomatic Illness (pp. 57-85).
Amsterdam: CIBA.

Gardner, R., Jr. (1982). Mechanisms in manic-depressive disorder. Arch
Gen Psychiatry, 39, 1436-1441.

Gut, E. (1989). Productive and Unproductive Depression. New York: Basic 
Books.  
 
Krebs, J. R., & Davies, N. B. (Ed.). (1984). Behavioral Ecology: An
Evolutionary Approach, Second Edition. Sunderland, MS: Sunderland.

Mayr, E. (1983). How the carry out the adaptationist program? Amer. 
Naturalist, 121 (March, 1983), 324-333.  
 
Nesse, R. M. (1990). Evolutionary explanations of emotions. Hum. Nature, 
1(3), 261-289.  
 
Nesse, R.M. (1991). What good is feeling bad? The evolutionary benefits
of psychic pain. The Sciences, Nov./Dec., 30-37.

Price, J. (1967). The dominance hierarchy and the evolution of mental 
illness. Lancet, 2, 243-246.  
 
Raleigh, M. J.,McGuire, M. T.,Brammer, G. L.,Pollack, D. B., & Yuwiler, A. 
(1991). Serotonergic mechanisms promote dominance acquisition in adult
male vervet monkeys. Brain Research 559:181-190.

Seligman, M. E. P. (1975). Helplessness: On Depression, development,
and death. San Francisco: W.H. Freeman.

Sober, E. (1984). Conceptual Issues in Evolutionary Biology. Cambridge,
Massachusetts: The MIT Press.

------------------------------

                             PSYCOLOQUY 
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                              Co-Editors:
 
(scientific discussion)         (professional/clinical discussion)
 
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Psychology Department  Graduate School of Applied   Graduate School of Applied
Princeton University   and Professional Psychology  and Professional Psychology
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                           Assistant Editor:

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                         Psychology Department
                         Princeton University
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