Evaluation of an Evolutionary Model of
Self-preservation and Self-Destruction
R. Michael Brown, PhD, Eric Dahlen, PhD, Cliff Mills, BA,
Jennifer Rick, BS, and Arturo Biblarz, PhD
According to decatanzaro’s mathematical model of self-preservation and self-destruction,
staying alive actually may reduce inclusive fitness for an individual who is low in reproductive potential and, at the same time, poses such a burden to close kin that it costs them
opportunities for reproduction. Predictions generated from this model were tested using
175 university students as subjects and variables constructed from a 164-item questionnaire. The criterion variables were separate measures of depression, hopelessness, and
suicide ideation and behavior. The predictor variables derived from the model were separate
measures of reproductive potential of the individual, the individual’s perceived benefit or
cost to kin, and reproductive potential of the individual’s kin. As predicted, there were
negative and significant bivariate correlations between each of the model-generated predictor variables and one or more of the criterion variables. Multiple regression analyses
showed that benefit to kin was the best predictor of both depression and hopelessness.
Discriminant analysis showed that reproductive potential of kin significantly differentiated
suicide attempters from nonattempters. Overall, our results support and extend decatanzaro’s model and empirical findings.
Drawing mainly upon Fisher’s (1950) concept of reproductive value, later refined
by Hamilton (1966), and upon Hamilton’s
(1964) notion of inclusive fitness, deCatanzaro (1986, 1987, 1991, 1992) has formulated a simple mathematical model
designed to explain the evolution of selfpreservative and self-destructive emotional and motivational mechanisms in
humans and other social species (e.g., social Hymenopterans). Stated simply, selfpreservation in an individual member of
a social species will be influenced by the
individual’s capacity for sexual reproduction, and by the individual’s ability to facilitate (or interfere with) reproduction in
kin. The model, in its original form (deCatanzaro, 1986), is represented mathematically as follows:
y,= P,+ CbLPLJ-L
where Y,= the optimal degree of self-preservation expressed by individual i
(the residual capacity to promote inclusive fitness);
pi = the remaining reproductive potential
of i;
P k = the remaining reproductive potential
of each kinship member k ;
bk = a coefficient ofbenefit (positive values
of b k ) or cost (negative values of bk) to
the reproduction of each k provided by
the continued existence of i (-1 < b < 1);
rk = the coefficient of genetic relatedness
of each k to i (sibling, parent, child=
.5; grandparent, grandchild, nephew or
niece, aunt or uncle = .25; first cousin =
.125; etc.).
R. Michael Brown is Psychology Professor, Eric Dahlen is a former student, Cliff Mills is a former student,
Jennifer Rick is a former student, and Arturo Biblarz is SociologyProfessor, Department of Psychology, Pacific
Lutheran University, Tacoma, Washington.
Address correspondence to R. Michael Brown, Department of Psychology, Pacific Lutheran University,
Tacoma, WA 98447.
Portions of this research were presented at the seventh annual meeting of the Human Behavior and
Evolution Society, Santa Barabra, California, June, 1995.
58
Suicide and Life-Threatening Behavior, Vol. 29(1), Spring 1999
0 1999 The American Association of Suicidology
BROWN ET AL.
Self-preservation (YJ is assumed to be
variable, ranging from "strong promotion
and defense of survival . . . to outright suicidal tendencies" (decatanzaro, 1991, p.
16).Where an individual lies on the distribution of self-preserving behavior is influenced by that individual's expected reproduction during his or her remaining
lifetime ( p i ) , and by the remaining reproductive value of the individual's kin (pJ,
weighted by degree of genetic relatedness
( r k )and by the benefit or cost to the reproductive value of the individual's kin provided by the continued existence of the
individual (bk).It should be noted that p
represents reproductive potential calculated from a given point in time forward;
it does not include offspring already produced. According to decatanzaro p is dependent on age, but will show variation
even within a given age cohort due to factors such as dominance, health, and adequacy of relationships with the opposite
sex.
In his discussions decatanzaro has focused mainly on the model's potential for
explaining the adaptive significance of
self-destructive behaviors (decatanzaro,
1986, 1987, 1992). Although positive Y,
values that approach 0 will be associated
with progressively weaker attempts at
self-preservation, negative '€', values raise
the possibility of outright self-destruction.
Negative Y, values will occur only when
the impact of the individual's continued
existence on the reproduction of closely related kin is so devastating that it overpowers his or her own residual reproductive
potential; that is, when bk is negative and
the absolute value of SkPkrk exceeds the
value of p i . It is assumed that, at some
level, the individual must be able to perceive predictive contingencies between behavior and reproductive outcomes, and
that this perception can influence gene expression.
DeCatanzaro (1981, 1991) has marshaled arguments and evidence from a variety of sources that make his model plausible. His own published survey data
(decatanzaro, 1984, 1995) have high-
59
lighted perceived burdensomeness to kin
and unstable heterosexual relationships
as potentially important predictors of suicide ideation. His 1984 survey of university students and the general public was
not a formal test of his model; rather, it
appears to have formed an empirical basis
for generating the model. The more recent
(1995) study reports survey data collected
from groups representing the general public, the elderly, psychiatric patients, criminal psychiatric patients, and homosexuals. Unfortunately, in 9 of the 11 groups
surveyed in this study, small sample sizes
(ns range from 27 to 70) relative to the
number of predictor variables (30) raise
serious questions about the reliability of
the regression findings. Also, decatanzaro has restricted his dependent variable
in these studies to a composite measure of
suicide ideation and behavior. While this
measure is clearly appropriate, there are
other components of self-destructive motivation and behavior that should also be
affected by Y, variables, namely, depression and hopelessness. Finally, although
decatanzaro raises the possibility of interactions among Y, variables, his theoretical
rationale fails to make them explicit, and
his empirical work reports no attempt to
assess such interactions. The present
study addresses these limitations and provides an independent and formal test of
the Yi model.
QUESTIONS AND HYPOTHESES
In his 1984 study, decatanzaro does not
report assessing the effects of perceived
benefithost to kin (b k )independently of
reproductive potential of kin ( p , ) . In fact,
his measure of the former appears to be
weighted by the latter, and by degree of
genetic relatedness of each kin member
summed over all kin (Xbkpkrk).
Whether
this same procedure was followed in the
1995 study is not clear, but there is no a
priori reason why the separate effects of
each variable (bkand Zpkrk)could not, or
60
SUICIDE AND LIFE-THREATENING BEHAVIOR
should not, be assessed. It is conceivable
that a sense of one’sperceived contribution
or burden to family is sufficient to drive
self-preserving or self-destructive cognitive and behavioral algorithms, independently of the number, reproductive status,
and genetic relatedness of kin who stand
to gain or lose by virtue of the individual’s
continued existence (assuming the number of kin is greater than 0). Similarly,
reproductive potential of kin may affect
self-preserving and self-destructive behaviors independently of one’s sense of
contribution or burden to kin. Moreover,
there are serious questions that can be
raised about the way in which CbkPkrk affects Y,in the model. When an individual’s
continued existence represents a contribution to kin, bk will be a positive number.
In this case Y ,will increase as the number
of kin, their reproductive potential, and
their degree of genetic relatedness to the
individual increase. However, when an individual’s continued existence represents
a burden to kin, bkwill be a negative number. In this case, Y t will decrease as the
number of kin, their reproductive potential, and their degree of genetic relatedness to the individual increase. DeCatanzaro does not present a rationale for the
model’s predicted paradoxical effect of Pkrk
on Y,. This is an unfortunate omission,
and a further reason for evaluating the
contributions of bk and CPkrk separately.
The results of such an evaluation might
argue for qualifying decatanzaro’s mathematical model in important ways.
Although decatanzaro (1992) acknowledges the possibility of complex interactions among Y, variables, to this point he
appears not to have discussed or evaluated
the interactions that are inherent in his
model:
1. Individual reproductive potential (p,)
should interact with perceived benefit/
cost to kin (bk),even though the additive
relationship specified in the model seems
to suggest otherwise. For example, if individual reproductive potential is extremely
low and bkis negative, then even negligible
increases in the absolute value of bk will
produce negative YLvalues and possible
self-destructive behavior. If individual reproductive potential is extremely high and
bk is negative, then the same small increases in the absolute value of bkwill not
have the same effect; much larger increases in bk will be required in order to
produce negative ‘r, values and possible
self-destructive behavior.
2. Reproductive potential of kin
weighted by degree of genetic relatedness
(Pkrk) should interact with benefitkost to
kin (bk),as indicated by the multiplicative
relationship between the two terms. Specifically, the effect of benefithost to kin on
Y, will not be the same at all levels of Pkrk.
Assume bk is negative (a perceived cost t o
kin associated with the continued existence of the individual) and pL2 0. An increase in the absolute value of bk from,
say, .2 to .4will result in a proportionately
steeper drop in Y L
values when Pkrk is high,
compared to when it is low.
Our first step in evaluating the model
and testing our hypotheses was to compute and examine all possible correlations
among our suicide-related measures, Y,
variables, and other relevant variables
that have proven t o be reliable correlates
of suicide-related measures in our own
work (Biblarz, Brown, Biblarz, Pilgrim, &
Baldree, 1991) and in the work of others
(e.g., Strang & Orlofsky, 1990; Topol &
Reznikoff, 1982). The Y t variables included a measure of individual reproductive potential, perceived benefit to kin,
and reproductive potential of kin. The
other relevant variables were perceived
quality of relationships with parents, perceived quality of relationships with
friends, and measures of locus of control.
Based on decatanzaro’s model, as well as
previous research, we expected our suicide-related measures to correlate negatively with individual reproductive potential, perceived benefit to kin, quality of
relationships with parents and friends,
and internal locus of control, and positively with external locus of control.
Our next step was to regress our suiciderelated measures on those variables that
BROWN ET AL.
61
of the opposite sex. The benefit-to-kin
items asked subjects to estimate the following: burdensomeness to family, impact
of their death on family, their contributions and assistance to family, and their
family’s dependence on them for emotional
or social support. Reproductive potential
of kin was a composite measure reflecting
each biological relative’s expected health,
fertility, and degree of genetic relatedness
to the subject, summed over all kin. The
METHOD
reproductive-potential-of-kin items asked
subjects to indicate how many of their bioSubjects
logical relatives were living for each of the
One-hundred and eighty one undergradu- following levels of kinship: parents, sibate students enrolled in psychology lings, children; grandparents, aunts and
courses at Pacific Lutheran University uncles, nieces and nephews; great grandvolunteered to participate in the study in parents, great aunts and great uncles,
return for course credit. The students were first cousins; second cousins. A parallel set
asked to complete a questionnaire and, of of items asked subjects to rate the health
those returned, 175 were usable (130 status of each kin member. Fertility ratwomen and 45 men). Subjects in the sam- ings were taken from U.S. Department of
ple were predominantly White (go%),reli- Commerce (1991) tables, and based on esgious (84% expressed a religious prefer- timated age cohorts of the subject’s kin.
ence), from an urban environment (68%), Genetic relatedness coefficients were asmiddle class (59% with annual family in- signed based on level ofkinship. Other relecomes 2 $40,000), first- or second-year vant predictor variables included quality of
students (64%), in late adolescence or relationships with parents (10 items),
early adulthood (89% ranged in age from quality of relationships with friends (7
17 to 23 years), single (81%),and hetero- items), and Levenson’s (1981) locus of
sexual (98%).
control inventory (24 items that yield
three scales: Internal, Powerful Others,
Chance). The remaining questionnaire
Questionnaire
items focused on demographic informaAll subjects completed a 164-item ques- tion, sexual behavior, and control issues.
tionnaire that included items designed to
assess affective states, cognitions, and be- Procedure
haviors of potential causal relevance to
suicide: depression (3 items), Beck’s Hope- Potential subjects were told that (1)the
lessness Scale (20 items; Beck, Weissman, purpose of the study was to assess relaLester, & Trexler, 19741, and a composite tionships among people’s attitudes, emomeasure of suicide ideation and behavior tions, and motivations; (2) the question(4 items). The Y ipredictor variables in- naire would require approximately 1hour
cluded individual reproductive potential or more to complete; (3) they would have
(4 items), perceived benefit to kin (6 4 days (which coincided with a midterm
items), and reproductive potential of kin break) to complete the questionnaire; (4)
(14 items). The individual reproductive po- they should feel free to omit questions that
tential questions asked subjects to rate the seem too difficult or to withdraw from parfollowing: importance of sex, hurtfulness ticipation at any time; and (5) they were
of romantic relationships, satisfaction to take the questionnaire seriously and rewith partners in romantic relationships, frain from talking to other participants
and perceived attractiveness to members about the questions. Those who volun-
had proven to be significant correlates of
these measures. Finally, we conducted a
second regression analysis which focused
exclusively on Y t variables as predictors
of our suicide-related measures. Our primary interest in this final analysis was to
evaluate the interactions that appear to
be specified by the model.
62
SUICIDE AND LIFE-THREATENING BEHAVIOR
teered were assigned random identification numbers and assured confidentiality.
dictors. Higher-order interaction terms
were dropped from the equation systematically following the step-down procedures
for testing interactions recommended by
Aiken and West (1991).
Design and Analysis
Correlations. The design was completely
correlational, and major analyses included bivariate correlations (Pearson r )
computed between each of the continuous
criterion variables (depression, hopelessness, suicide ideation and behavior) and
each of the eight predictor variables (individual reproductive potential, benefit to
kin, reproductive potential of kin, quality
of relationships with parents, quality of
relationships with friends, internal locus
of control, belief in powerful others locus
of control, belief in chance locus of control).
First Regression Analysis. The purpose of
the first regression analysis was to evaluate the contribution of each of the Yivariables alongside other predictor variables
that have proven to be reliable correlates
of hopelessness in previous research. Separate stepwise multiple regressions of depression, hopelessness, and suicide ideation and behavior were computed. For
each of the three regressions, only those
variables that had proven to be significant
(two-tailed)correlates ofthe criterion variable being regressed were entered as predictors in the equation. Finally, a discriminant analysis was computed to determine
which of the eight predictor variables reliably differentiated self-reported suicide
attempters from nonattempters.
Second Regression Analysis. The second
regression analysis focused exclusively on
the potential contributions of Y Lvariables
to our criterion measures. Of particular
interest was the assessment of hypothesized interactions among the Y:variables.
Separate regressions were performed on
each of the suicide-related measures, with
the effects of the remaining two criterion
variables removed before proceeding
further. Subsequently, each of the Y ,variables, and all possible interactions involving these variables, were entered as pre-
RESULTS
Correlations with SuicideRelated Measures
Each of the three 'Pivariables correlated
significantly' with one or more of the suicide-related measures, and the significant
correlations were all in the direction predicted by decatanzaro's model (see Table
1).Subjects with lower individual reproductive potential scores were more likely
than other subjects to report higher levels
of depression and suicide ideation and
behavior. Subjects with fewer fertile,
healthy, and closely related kin were more
likely than others to report higher levels
of suicide ideation and behavior. Subjects
with lower benefit to kin scores were more
likely than others to report higher levels
of depression, hopelessness, and suicide
ideation and behavior.
For the other relevant variables, subjects scoring lower on quality of relationships with parents and with friends were
more likely than others to score high on
all three suicide-related measures; subjects scoring lower on internal and higher
'Reported correlations and regression findings were
calculated on the entire sample. Because marital status could alter subjects' responses, especially to the
individual reproductive potential items, we also analyzed data with married subjects excluded from the
sample. Regression findings were identical (direction
and significance of predictors) to those of the entire
sample. Four of the correlational findings differed
from those of the entire sample: the correlation between individual reproductive potential and suicide
ideation and behavior only approached significance,
r(133)= -.17,p c .057;the correlation between relationships with friends and suicide ideation and behavior was not significant, r( 158)= -. 12;the intercorrelation between individual reproductive potential
and relationships with parents was not significant,
r(132)= .13;the intercorrelation between individual
rerpoductive potential and relationships with friends
was not significant, r(132)= .14.
63
BROWN ET AL.
TABLE 1
Correlates of Suicide-Related Measures
Suicide variables
Correlates
Individual reproductive potential
Benefit to kin
Reproductive potential of kin
Parents
Friends
Internal locus of control
Powerful Others locus of control
Chance locus of control
Depression
Hopelessness
Ideation and
behavior
-.29***
-.44***
-.04
-. 19*
-
-.08
-.47***
.01
-.27***
-.39***
-.38*"*
-.21**
-.14
-.28***
-.20**
-.38***
-.18*
-.08
.22**
.28***
.23**
.35***
-
5o*w
-.03
.08
Note. All probability levels are two-tailed.
*p < .05; **p < .01;***p < ,001.
on external locus of control measures were
more likely than others to score high on one
or more of the suicide-related measures.
Intercorrelations
As expected, the three suicide-related
measures were positively correlated with
one another. For depression and hopelessness, 4171) = .20, p < .008;for depression
and suicide ideation and behavior, r(170)
= .45, p < .001;and for hopelessness and
suicide ideation and behavior, r(172) = .13,
p < .079. As for the Yi variables, subjects
with lower individual reproductive potential scores were more likely than others
to report poor relationships with parents,
r(143) = .26, p < .001, and with friends
r( 143) = .22, p < .008. Similarly, subjects
with lower benefit-to-kin scores reported
poorer relationships with parents, 4171)
= 5 7 , p < .001, and with friends r(171) =
5 2 , p < .001. Finally, subjects with low
benefit-to-kin scores tended to score low
on internal, and high on external, locus
of control: Internal, 4172) = .21, p < .005;
Powerful Others, 4172) = -.16, p < .035;
Chance, r(172) = -.23, p < .002. Reproductive potential of kin showed no significant
intercorrelations.
First Regression Analysis
Results of multiple regressions of each criterion variable underscore the contribu-
tions of one or more of the Y Lvariables
when compared with other relevant and
traditionally potent predictors (see Table
2). Compared to the other seven predictor
variables, benefit to kin was the strongest
predictor of depression, accounting for
nearly 25%of the variance. Moreover, benefit to kin was the only significant predictor of hopelessness, accounting for just
under 20%of the variance. Individual reproductive potential was a significant predictor of depression, and reproductive potential of kin was a significant predictor
of suicide ideation and behavior. The other
significant predictors were quality of relationships with parents and the chance locus of control measure. Each of these variables reliably predicted both depression
and suicide ideation and behavior. Results
of the discriminant analysis indicated that
six of the eight predictor variables reliably
differentiated suicide attempters from
nonattempters (see Table 3). Reproductive
potential of kin was the most potent of the
significant predictors based on an examination of correlations between the
discriminant scores and the predictor (independent) variables. Compared to nonattempters, attempters had significantly
fewer close kin with high expected fertility
and good health. Interestingly, compared
to nonattempters, attempters had significantly higher individual reproductive potential scores. The two groups did not differ significantly on the benefit-to-kin
SUICIDE AND LIFE-THREATENING BEHAVIOR
64
TABLE 2
First Regression Analysis: Stepwise Multiple Regressions Comparing the Effects of Y,
Variables with Those of Other Relevant Predictor Variables
Suicide variable
Depression
Hopelessness
Ideation and
behavior
Step
F
Adj. R2
Predictor
P
t
1
2
3
46.28***
36.93***
29.16***
.25
.34
.38
-.29
.29
-.21
-3.61***
4.23***
-2.58*
4
1
23.66***
42.50***
.39
.20
Benefit to kin
Chance
Parents
Individual reproductive
potential
Benefit to kin
-. 15
-.45
-2.18*
-6.52***
1
2
19.02***
16.90***
.ll
.19
-.29
.26
-3.8 1***
3.40***
3
13.65***
.21
Parents
Chance
Reproductive
potential of kin
-. 18
-2.44*
Note. All probability levels are two-tailed.
*p < .05;**p < .01;***p < ,001.
variable, though the group means were
in the expected direction, with attempters
showing lower scores ( M = 23.625) than
nonattempters ( M = 24.632).
Second Regression Analysis
Results of multiple regressions of each suicide-related measure using only the Yz
variables as predictors showed no support
for the two hypothesized interactions: individual reproductive potential x benefit
to kin, or reproductive potential of kin x
benefit to kin. However, for each of the
suicide-related measures, at least one of
the Y ivariables attained significance as
a predictor (see Table 4).As in the first
regression analysis, benefit to kin was a
significant predictor of both depression
and hopelessness. Individual reproductive
potential also predicted depression significantly. Reproductive potential of kin was
the only significant predictor of suicide
ideation and behavior.
TABLE 3
Discriminant Analysis: Differentiation of Suicide Attempters from Nonattempters
~~~
~
~
suicide
attempters
Means for nonattempters
Wilks’s
( n = 8)
( n = 133)
Lambda
Discriminant
correlations
with
predictors
Chance
3.14
32.88
31.12 ’
14.50
3.97
37.61
30.38
11.82
.95**
.94*
.93*
.92*
.71
.37
-.13
-.34
Individual reproductive potential
Powerful others
7.62
13.00
7.38
12.71
.91*
.91*
-.08
Means for
Step
significant
independent
variables
Reproductive potential
1
2
3
4
5
6
of kin
Parents
Friends
Note. All probability levels are two-tailed.
*p < .05;**p < .01;***p < .001.
-.04
BROWN ET AL.
65
TABLE 4
Second Regression Analysis: Multiple Regressions Evaluating the Effects of the
Variables and Hypothesized Interactions among These Variables
Adj. R2
Predictor
s
t
10.71***
.35
-.38
-4.50***
Hopelessness
7.55***
.27
Benefit to kin
Individual reproductive
potential
Benefit to kin
Reproductive potential
-.17
-.55
-6.56***
Ideation and behavior
6.58***
.24
-.19
-2.50"
Suicide variable
Depression
F
of kin
-2.34*
Note. All probability levels a r e two-tailed.
*p < .05; **p < .01;***p < ,001.
to suicide ideation, hopelessness has been
shown in prospective studies to be a far
Perceived Benefits and
better predictor of suicide (Beck, Steer, KoCosts to Kin
vacs, & Garrison, 1985), and is arguably
Our benefit-to-kin variable correlated sig- the best predictor overall of suicide comnificantly with all three suicide-related pletions in clinical populations (Steer, Kumeasures-depression, hopelessness, and mar, & Beck, 1993). The fact that benefit
suicide ideation and behavior. In addition, to kin is related inversely not only to suicompared to the seven other predictor cide ideation but also to hopelessness
variables, benefit to kin explained more raises the odds that we are tapping into a
of the variance in depression and hopeless- motivational path that can eventuate in
ness. Other researchers operating from actual suicide, not just thoughts about suivery different theoretical perspectives cide or parasuicide.
have also reported evidence for a relationGiven the correlational design of our
ship between perceived burdensomeness study, we can only speculate about the post o others and self-destructive behavior sible causal role of perceived benefits and
(Motto & Bostrom, 1990; Woznica & Sha- costs to kin. It may well be that, in some
piro, 1990).
instances, perceiving oneself to be a burThe benefit-to-kin findings are quite den to kin elevates depression and hopeconsistent with decatanzaro's model lessness and activates a self-destructive
(19861, and provide a needed extension of motivational system. However, it is also
his empirical work linking burdensome- possible that the causal arrow points in
ness to kin with suicide ideation (deCa- another direction; specifically, high levels
tanzaro, 1984, 1995). Suicide ideation is of depression may cause a person to think
clearly an appropriate measure of self-de- of himself or herself as a burden. In short,
structive cognitive content. However, the perceived burdensomeness may be an efextent of ideation in nonclinical adolescent fect rather than a cause of depression. This
and young adult populations (e.g., 44% in could explain why benefit to kin was a
Rudd, 1989; 63% in Smith & Crawford, potent predictor of both depression and
1986; 61% in Strang & Orlofsky, 1990) hopelessness in our study. However, there
raises serious questions about its ability are other lines of evidence that oppose this
to predict actual suicide, and its role in the interpretation, and which suggest that
motivational sequences that eventuate in burdensomeness can have a causal influsuicide. Although most suicides probably ence that is not contaminated by subjects'
have a history of ideation, the vast major- affective states:
ity of even serious ideators never attempt,
1.Extremely high benefit-to-kin scores
let alone complete, suicide. And, compared and extremely low depression scores were
DISCUSSION
66
SUICIDE AND LIFE-THREATENING BEHAVIOR
rare in our study. The mean total benefitto-kin score was high (24.75 out of a possible 301, while the mean total depression
score was low (3.905 out of a possible 16).
These data do not support the conclusion
that depression was responsible for relatively low benefit-to-kin scores, but they
do not rule out the possibility that changes
within the observed range of depression
ratings may have influenced the benefitto-kin responses in some way.
2. When regressing a given dependent
variable (e.g., hopelessness), we partialed
out the effects of the other dependent variables (depression, suicide ideation and behavior). Therefore, the observed significant regression of hopelessness on benefit
to kin indicates that benefit to kin made
a unique contribution to the variance in
hopelessness. This argues against the conclusion that subjects’ depression ratings
can explain the predictive relationship between benefit to kin and hopelessness.
3. In a recent study, we (Brown, Brown,
Johnson, & Lampert, 1997) manipulated
experimentally the degree to which a target person in a scenario represented a
burden to kin, while keeping the target
person’s described level of depression constant across all conditions of the experiment. As predicted, we found that university students judged the target person to
be significantly more unhappy, hopeless,
and suicidal if, in the scenario, the target
was depicted as being a burden (compared
to a benefit) to kin. Furthermore, subjects’
depression levels, as measured by the Beck
Depression Inventory (Beck, 1967),did not
predict their ratings of the target person’s
unhappiness, hopelessness, or suicidal intent. These data show clearly that perceived burdensomeness can have a causal
influence on ratings of depression, hopelessness, and suicidal intent in others.
At first glance, it is perhaps surprising
that benefit to kin, so strongly associated
with our continuous suicide-related measures, failed to differentiate suicide attempters from nonattempters. However,
this “failure” may have occurred in part
because of the difficulties inherent in taking retrospective measures of self-destruc-
tive behavior. Maris (1992) has noted that
nonfatal suicide attempts may confer on
the attempter benefits as well as costs.
Benefits include attention from family
members, friends, and professionals, and
short-term elevation of affect. Such benefits may have reduced feelings of burdensomeness in our attempters. It is also possible that some of our attempters were not
intent on completing suicide but, rather,
were motivated by the increased attention
they anticipated receiving as a result of
their “attempt” (Kreitman, 1977). In an
effort to clarify this matter we are now
conducting studies that utilize a revised
questionnaire designed to rate the lethality of any reported suicide attempts.
Reproductive Potential of Kin
Our data also show that reproductive potential of kin may be an important variable in its own right. It was a significant
inverse predictor of suicide ideation and
behavior, whether entered alongside all of
our other predictors, or only with Yi variables. Moreover, it did the best job of all
our predictors differentiating suicide attempters from nonattempters, revealing
that attempters had significantly fewer
fertile, healthy, and genetically related kin
than were reported by nonattempters. The
direction of this relationship is consistent
with decatanzaro’s model as long as bk is
assumed to be the same (and not a negative value) for both attempters and nonattempters. Our data provide no reason to
doubt these assumptions. Attempters and
nonattempters did not differ significantly
on benefit to kin scores, and the distribution of benefit to kin scores was skewed
negatively.
Our reproductive-potential-of-kin variable is likely not a proxy for size of an
individual’s immediate family (parents
and siblings), even though family size is
reflected in calculating reproductive potential of kin. Our questionnaire measured family size in a separate item, and
the pattern of correlations between it and
other variables was not consistent with
the reproductive-potential-of-kin pattern.
BROWN ET AL.
Although family size correlated positively
and significantly with reproductive potential of kin, it did not correlate significantly
with depression, hopelessness, or suicide
ideation and behavior. It should be noted,
however, that family size, as measured by
number of offspring, has been found to be
an inverse predictor of attempted suicides
(Calzeroni, Conte, Pennati, & Vita, 1990;
Koller & Costanos, 1968; Kreitman, 1977;
Lipe, Schulz, & Bird, 1993), and of completed suicides (Hoyer 8z Lund, 1993;
Humphery, 1977; Iga, Yamamoto, Noguchi, & Koshinaga, 1978).
Individual Reproductive
Potential
Our measure of individual reproductive
potential was inversely related to depression, consistent with decatanzaro’s model.
In both regression analyses, individual reproductive potential was a significant
source of variance in predicting depression. Naturally, the same cautions that
were raised over interpretation of the benefit-to-kin findings also apply to the individual reproductive potential data. We do
not know to what extent subjects’ affective
states may have colored their assessments
of relationships with, and attractiveness
to, members of the opposite sex. However,
as noted before, subjects’ levels of depression were low overall, and this suggests
that depression was not likely responsible
for relatively low scores on the individual
reproductive potential items.2
‘More objective indicators of individual reproductive
potential, such as age and resources, would be less
susceptible to contamination by subjects’ affective
states. We collected age data, but the range was too
restricted to expect age-related differences in reproductive potential, actual or perceived. We also collected resource data yielding two measures: subject
ratings of family economic status relative to others,
and reported occupational status of parents weighted
by ratio of reported family income to reported family
size. High ratings of relative family economic status
were accompanied by low suicide ideation and behavior, even with the effects of depression and hopelessness partialed out, r(152) = -.19, p < .019. When the
partial correlation was recalculated for each gender,
only males showed a signficant effect, r(35) = -.37,p
67
In the discriminant analysis, individual
reproductive potential was one of six
predictor variables that reliably differentiated suicide attempters from nonattempters. Suicide attempters had higher
individual reproductive potential scores
than nonattempters, a finding that seems
at odds with the correlation and regression
results from all 175 subjects. With so few
attempters, it is difficult to know whether
this finding reflects sampling error, or a
reliable difference between attempters
and nonattempters. However, the same
discriminant analysis showed a similar reversal of correlational findings for quality
of relationships with friends: Attempters
were differentiated from nonattempters
by their better relationships with friends,
but correlations for the entire sample
clearly indicate an inverse relation between relationships with friends and each
of our three continuous suicide-related
measures. One possible explanation of
these findings was presented earlier, in
connection with the failure of the benefitto-kin variable to reliably differentiate attempters from nonattempters. Ratings of
sex, romantic relationships, and personal
attractiveness may have improved as a
consequence of the suicide attempt. In order to test this hypothesis, prospective
< .025. Subjecting our second, ostensibly more objective, resource measure to the same analyses yielded
similar results. The partial correlation between income-weighted occupational status and suicide ideation and behavior was significant for males, r(26)
= -.40,p < ,037, but was negligible for females.
Neither resource measure appears to have been influenced significantly by our measure of subjects’ depression or scores on Beck’s Hopelessness Scale, yet
each resource measure correlated with suicide ideation and behavior in ways expected by deCatanzaro’s evolutionary model. The fact that the correlations were observed for males only is consistent with
an empirically defensible evolutionary perspectivesexual selection theory-which predicts that women
will value men mainly for their ability to provide
resources, while men will value women mainly for
their physical attractiveness, a presumed sign of
health and reproductive capacity (Archer, 1996).Not
surprisingly, in our study male subjects’ ratings of
their physical attractiveness correlated little, if a t
all, with the dependent measures. On the other hand,
female subjects’ attractiveness ratings correlated
significantly with both depression, r(130) = -.26, p <
,003, and with suicide ideation and behavior, r(129)
= -.25, p < ,005.
68
SUICIDE AND LIFE-THREATENING BEHAVIOR
studies are needed in which measures of
individual reproductive potential are
taken prior to, as well as after, nonfatal
suicide attempts.
tional substrates of self-preservation lie on
a continuum. Therefore, a priori, it seems
reasonable to expect that such differences
would be correlated with fitness variables
regardless of which portion of the selfpreservation continuum is sampled. In
fact. our data indicate that the exDected
correlations hold for subjects who score
high on self-preservation (i.e., they show
low levels of depression and hopelessness
overall). The correlations also appear to
hold for certain populations at risk for selfdestruction (decatanzaro, 1995). Only
further empirical work of a prospective nature can determine whether there is a connection between fitness and self-preservation motivation in suicide completers.
Because reproductive value (expected
future reproduction) peaks during adolescence (Thornhill & Thornhill, 1983) and
declines sharply with age, and because reproductive strategies are expected to vary
with sex (Trivers, 1972), we might expect
differential effects of fitness variables on
self-destructive motivation and behavior
depending on age and sex. In his recent
work with six (nonuniversity) samples
representing the general public, deCatanzaro (1995) has found that the strongest fitness correlates of suicide ideation
do, in fact, change depending on age and
sex of the sample. For example, self-reported health and financial status failed
to correlate significantly with suicide ideation in men or women comprising the
youngest samples (18-30 years of age).
However, these two variables were significant inverse correlates of ideation for both
men and women in the older samples
(31-50 years, and 51+ years). Furthermore, one or more measures of sexual activity correlated significantly and inversely with ideation in each of the male
samples, regardless of age, but only in the
youngest female sample. It should be emphasized, however, that perceived burdensomeness toward kin correlated significantly and positively with suicide ideation
in all six samples, in four of five additional
“atr i s k samples, and in a university sample tested previously (decatanzaro, 1984).
Interactions
Our hypothesized interactions-individual reproductive potential x benefit to
kin, and reproductive potential of kin x
benefit to kin-were not confirmed for any
one of the suicide-related measures. Perhaps this is because of restricted variation
in the benefit-to-kin scores. Even though
these scores ranged from 8 to 30 (possible
range: 0-30),the distribution was skewed
negatively (67% of the scores were above
the mean). Therefore, interactions involving benefit to kin may have been obscured
by this ceiling effect. It will be necessary
to explore the full range of the benefit-tokin variable, perhaps with clinical samples, in order to properly evaluate the hypothesized interactions.
Qualifications Concerning
the Sample
Naturally, our generalizations are limited
to a rather restricted population-young
psychology undergraduates attending a
private (Lutheran) university in a major
metropolitan area in the Pacific Northwest region of the United States. Furthermore, the sample represents a population
that is disproportionately female, White,
single, middle- to upper-middle class, at
the peak of fertility and, overall, not suffering from clinical depression or other serious psychopathological disorders. Thus,
we are limited in what we can say about
suicide completers, and about individuals
with demographic characteristics (e.g.,sex
and age) that differ from those of our
sample.
Even though our sample precludes generalizing our findings directly to individuals who complete suicide, the model we
are testing assumes that individual differences in evolved emotional and motiva-
BROWN ET AL.
This consistent pattern is strengthened by
the independent benefit-to-kin findings
from the present study and from other recent investigations using different samples and methodologies (Brown & Melver,
1996; Brown et al., 1997).
Qualifications Concerning the
Evolutionary Model
DeCatanzaro’s model was designed with
ancestral conditions in mind, when humans lived in relatively small and genetically interrelated groups. According to the
model, suicide would have been genetically advantageous only when there was a
conjunction of low individual reproductive
potential and burdensomeness toward
kin. However, it is important to note that
our present environment may differ dramatically from the environment of evolutionary adaptedness, as decatanzaro
(1995) and others (e.g., Tooby & Cosmides,
1992)have noted. There exist today methods of self-destruction, threats to family
and society, and modes of communication
and isolation that were not present in the
ancestral environment. Consequently, we
should expect that there may now be alternative paths to suicide. Some instances of
suicide in the contemporary environment
may be triggered by experimentation, media stories, ineffective strategies for coping with evolutionarily novel stress, or
psychopathological processes.
Clinical Implications
An evolutionary approach to suicide offers
new and potentially fruitful ways of understanding the etiology of suicide. The
“almost bewildering array of conditions”
(Felner, Adan, & Silverman, 1992) linked
to suicide may have in common the fact
that they are actual or perceived threats
to inclusive fitness (e.g., parent-child conflict, death of a family member, breakup of
a romantic relationship, terminal illness,
public humiliation), or reactions to such
threats (e.g., substance abuse, affective
69
disorders, conduct disorders). The threats
and reactions by themselves are not sufficient to drive suicidal behavior; they may
in fact produce a wide variety of outcomes.
What would make a person truly suicidal,
according to the evolutionary model outlined in the present study, is the (unconscious or conscious) calculation^' that the
potential genetic costs of staying alive outweigh the gains. Extrapolating from the
model, this result would occur only when
expected individual reproduction is extremely low, and feelings of burdensomeness to close kin are high. Perhaps it is
the negative outcome of a fitness analysis
such as this that triggers a state of hopelessness.
Our findings and decatanzaro’s underscore the importance of understanding interpersonal relationships within the family in treating depression, hopelessness,
and self-destructive ideation and behavior. It appears that self-reported burdensomeness to family members is a salient
correlate of suicide ideation and behavior
for both genders and all age levels sampled
thus far, whether university students, the
general public, or a variety of at risk populations. It may be useful to evaluate and
attempt to modify perceptions of burdensomeness in depressed or otherwise atrisk individuals. Cognitive-behavioral
techniques might be used to help such individuals identify fallacious conclusions of
burdensomeness, attend to and rehearse
instances of concrete contributions made
to family members, and take advantage of
opportunities for making contributions to
the community or society. Relatives of a
depressed individual may communicate
messages of burdensomeness directly, or
through emotional neglect. Therefore, it
may be especially important to include the
depressed person’s siblings, parents, offspring, or other family members in treatment plans. In this way, family members
might learn to recognize their roles in communicating overt or subtle messages of
burdensomeness to the depressed relative,
and to appreciate the potentially lethal
impact of such communications.
70
SUICIDE AND LIFE-THREATENING BEHAVIOR
CONCLUSIONS
that have occurred in the social ecology of
our species.
Freud‘s use of the “death instinct” to explain self-destructive behavior met with
skepticism and denial among analysts and
biologists alike almost as soon as the concept was introduced in the early 1900s
(Jones, 1957).In the years hence, conceptualizations linking suicide to biology typically have stated or implied that genes
may be responsible for affective disorders
that can give rise to suicide, but not for
suicide directly. The idea that at least
some aspects of self-destructive motivation may be part of our evolutionary heritage has received little attention, let alone
support, in spite of suggestive evidence
from behavioral genetic studies (e.g.,
Schulsinger, Kety, Rosenthal, & Wender,
1979), the availability of kin selection as
an explanatory mechanism (Hamilton,
1964; Maynard Smith, 1964),and the formulation of inclusive fitness models of animal suicide (McAllister & Roitberg, 1987;
O’Connor, 1978; Poulin, 1992). The lone
voice in the wilderness belongs to deCatanzaro, whose arguments for the evolution of self-destructive behavior under
well-defined circumstances seem plausible, and whose mathematical model has
provided the impetus for the present study.
Results of our study support and extend
decatanzaro’s theoretical and empirical
contributions (decatanzaro, 1984, 1986,
1995). While his investigations focused
only on suicide ideation and suicide attempts as dependent measures, our study
has shown that one or more of the three
Y ivariables predict levels of depression
and hopelessness as well. Moreover, although decatanzaro appears not to have
considered reproductive potential of kin
an important variable in its own right, our
regression and discriminant analysis results show it to be a significant predictor
of suicide ideation and behavior. Finally,
although decatanzaro has been careful to
note that the Y imodel was intended to
explain the adaptive significance of suicide in ancestral conditions, our data (and
his) suggest that the model has predictive
utility today, in spite of dramatic changes
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Received: January 17, 1997
Revision Accepted: December 24, 1997