What's in a Name: Is "Evolutionary Psychology" Eclipsing "Sociobiology" in the Scientific Literature?

Evolutionary Psychology
www.epjournal.net – 2007. 5(4): 683-695
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Original Article
What’s in a Name: Is “Evolutionary Psychology” Eclipsing “Sociobiology” in
the Scientific Literature?

Gregory D. Webster, Department of Psychology, University of Illinois at Urbana-Champaign, Champaign, IL
61820, USA. Email: webster3@uiuc.edu (Corresponding author)
Abstract: Is the term “evolutionary psychology” supplanting “sociobiology” in the
scientific literature? How influential was E. O. Wilson’s (1975) book, Sociobiology, in
establishing the discipline of the same name? Similarly, how influential were the two
Tooby-Cosmides chapters appearing in The Adapted Mind (Cosmides and Tooby, 1992;
Tooby and Cosmides, 1992) in establishing evolutionary psychology as a viable outgrowth
of sociobiology? The purpose of the present research was to answer these questions using
quantitative analyses of publication trends. The Internet search engine Google Scholar was
used to count the number of hits (i.e., the number of scholarly works, citations, etc.) for
“sociobiology” and “evolutionary psychology” separately per year from 1960 to 2003.
Interrupted time-series analyses revealed significant increases (intercept shifts) for
sociobiology hits between 1974 and 1975, and for evolutionary psychology hits between
1991 and 1992. Evolutionary psychology hits also experienced a significant increase in
change-over-time (a slope shift) between 1991 and 1992. Growth curve analyses revealed
that the rate of growth for evolutionary psychology, which was accelerating over time, was
significantly greater than that for sociobiology, which was decelerating. The implications
of these findings for understanding the histories of sociobiology and evolutionary
psychology are discussed.
Keywords: evolutionary psychology, history of science, interrupted time-series analysis,
publication trends, sociobiology
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Introduction
The purpose of the present research was to quantify and compare two key developments in
evolutionary science that emerged during the latter half of the twentieth century:
sociobiology and evolutionary psychology (see Table 1 for sample definitions).


Sociobiology, pioneered by E. O. Wilson (1975) in his landmark book of the same name,
challenged conventional thinking about the biological emergence of social behavior and

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Is Evolutionary Psychology Eclipsing Sociobiology?

forced many social scientists to consider the biological determinants of behavior. Following
its 1975 publication, Sociobiology inspired numerous researchers to re-evaluate their
models of animal—and occasionally human—behavior. The word “sociobiology” soon
became incorporated into the scientific vernacular. For example, the scientific journal
Evolution and Human Behavior was entitled Ethology and Sociobiology from its founding
in 1979 until new editors adopted a more anthropocentric perspective in 1997.
Sociobiology has had a profound impact on evolutionary science since 1975 and continues
to influence evolutionary research today.

Table 1. Sample definitions of sociobiology and evolutionary psychology.
Definitions
Term
Dictionary.com
American Heritage Dictionary
The study of social behavior in The study of the biological
animals with emphasis on the role determinants of social behavior,
of behavior in survival and based on the theory that such
Sociobiology
reproduction, engaging branches behavior is often genetically
of ethology, population genetics, transmitted and subject to
and ecology.
evolutionary processes.
The study of the psychological
The branch of psychology that
adaptations of humans to the
studies the mental adaptations of
changing physical and social
Evolutionary
humans to a changing
environment, especially of changes in
Psychology
environment, especially
brain structure, cognitive
differences in behavior, cognition, mechanisms, and behavioral
and brain structure.
differences among individuals.

Evolutionary psychology was in some ways an outgrowth of sociobiology. Not only
did evolutionary psychology provide answers to some of the criticisms of sociobiology, but
it also took an anthropocentric focus that drew on cognitive science and biological
anthropology. Whereas sociobiology was built on social insect models, evolutionary
psychology would be built on studies of humans. Arguably two of the most-cited works in
evolutionary psychology have been the two chapters in The Adapted Mind (Barkow,
Cosmides, and Tooby, 1992) coauthored by John Tooby and Leda Cosmides: “The
Psychological Foundations of Culture” (Tooby and Cosmides, 1992) and “Cognitive
Adaptations for Social Exchange” (Cosmides and Tooby, 1992). For many researchers,
these chapters crystallized what had previously been a loose amalgamation of evolutionary
perspectives on human behavior. Following their 1992 publication, the term “evolutionary
psychology” and its Darwinian perspectives became adopted by many researchers in the
human social sciences. Shortly thereafter, popular textbooks (e.g., Buss, 1999) and a
scientific handbook (Buss, 2005) championed the no-longer-nascent discipline of
evolutionary psychology. The Adapted Mind chapters coauthored by Tooby and Cosmides
in 1992 remain indispensable citations for evolutionary psychologists today.
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Is Evolutionary Psychology Eclipsing Sociobiology?

Although Wilson’s (1975) book was an obvious candidate for a tipping-point (cf.
Gladwell, 2000) in the development of sociobiology, the extent to which the Tooby-
Cosmides chapters provided a similar boost to evolutionary psychology was comparatively
less clear. To this end, preliminary analyses of citations in the PsycINFO abstract database
revealed that the two Tooby-Cosmides chapters had been cited 386 (Tooby and Cosmides,
1992) and 326 (Cosmides and Tooby, 1992) times as of September 2007 (M = 356, SD =
42.43). In comparison, the other 16 chapters in The Adapted Mind had only been cited an
average of 34.06 times (SD = 20.03)—significantly less than the Tooby-Cosmides chapters
(
2
t16= 19.42, p < .001, R = .96). An additional PsycINFO search of all works published
from 1990 to 1994 revealed that the two 1992 Tooby-Cosmides chapters were also the
most-cited works relating to “evolutionary psychology” published during that time. Thus, it
appears that the Tooby-Cosmides chapters from The Adapted Mind may have indeed been
key works in the promotion and development of evolutionary psychology as a viable
scientific discipline.
But what can these great works tell us about their respective impacts on
sociobiology and evolutionary psychology over time? Feist (2006) recently chronicled the
history of another emerging field: the psychology of science (see also Simonton, 1988).
Feist proposed that the other three meta-sciences (i.e., the philosophy, history, and
sociology of science) each had key events such as the establishment of peer-reviewed
journals and regular conferences that facilitated their development. Using the Google
Scholar search engine and interrupted time series analyses, Webster (2007a) empirically
showed that establishing a journal was indeed key to an emerging meta-science’s viability,
whereas regular conferences were not. The present research adopted Webster’s (2007a)
methodologies to quantify and test whether Wilson’s (1975) Sociobiology and the Tooby-
Cosmides (1992) chapters from The Adapted Mind had a significant impact on the
emergence of sociobiology and evolutionary psychology, respectively.
The purpose of the present research was to test some of the assertions mentioned
above using quantitative analyses of publication trends. Specifically, given the historical
events, theoretical perspectives, and empirical research cited above, three specific
predictions were developed:
1. E. O. Wilson’s (1975) book would lead to a significant and immediate increase
(intercept shift) in Google Scholar hits for “sociobiology” following its publication.
2. The Tooby-Cosmides chapters from 1992’s The Adapted Mind would lead to a
significant and immediate increase (intercept shift) in Google Scholar hits for
“evolutionary psychology” following its publication.
3. Evolutionary psychology’s increasing empiricism (Webster, 2007d) and recent
penetration into the scientific literature (Webster, 2007a, 2007b) would result in it
having a significantly greater rate of increase over time than sociobiology.
Method
The Internet search engine Google Scholar was used to count hits for scholarly
works in which the terms “sociobiology” and “evolutionary psychology” were mentioned
Evolutionary Psychology – ISSN 1474-7049 – Volume 5(3). 2007. -685-

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Is Evolutionary Psychology Eclipsing Sociobiology?

(separately) each year from 1960 to 2003 (44 years). Google Scholar was chosen over
PsycINFO because the latter would have underestimated counts for “sociobiology” due to
the fact that PsycINFO is inherently psychology-focused, whereas many works pertaining
to sociobiology appear in biological and anthropological publications that are not indexed
by PsycINFO. In contrast, Google Scholar provides a more global, comprehensive search
tool that draws on all areas of science and allows for a fairly unbiased comparison of
publication trends between sociobiology and evolutionary psychology.
To avoid conflating counts by including articles in which both terms occurred, a
conservative approach was taken by searching for “sociobiology” without “evolutionary
psychology,” and for “evolutionary psychology” without “sociobiology.” The year 1960
was chosen because it allowed for a baseline to be established prior to the publication of E.
O. Wilson’s (1975) landmark book. The year 2003 was chosen because there is a lag in the
time it takes for articles and their citations to be indexed on Google Scholar, which
catalogues thousands of books and journals. This method allowed for interrupted time-
series analyses to be conducted.
To compare growth curves over time between hits for sociobiology and
evolutionary psychology, a three-year moving average was calculated to smooth-out some
of the short-term fluctuations; this reduced the year range to 42 years (1962–2003; cf.
Webster, 2007b). Following procedures outlined by Webster (2007a), the three-year
moving averages were then log10 transformed because the frequency counts for both terms
tended to grow exponentially over time. The log-transformed moving average hits were
then modeled using standard longitudinal growth curve regression techniques (cf. Cohen,
Cohen, West, and Aiken, 2003; Judd and McClelland, 1989; Singer and Willett, 2003).
Results
Following procedures outlined by Shadish, Cook, and Campbell (2002), interrupted
time series analyses were performed to determine the extent of the impact of Wilson’s
(1975) book and the two Tooby-Cosmides (1992) chapters as landmark works on
sociobiology and evolutionary psychology, respectively. Interrupted time series analyses
allow for the assessment of discontinuities in intercepts (mean shifts) and slopes (trend
shifts) over time (see Appendix for details). Log hits for sociobiology shot up significantly
following the publication of Wilson’s (1975) sensational book (a mean shift); however,
following this initial spike, sociobiology grew less rapidly, resulting in a significantly less
positive change-over-time slope since 1975 (a slope shift; Table 2, Figure 1). Log hits for
evolutionary psychology also increased significantly following the publication of Tooby
and Cosmides’ (1992) influential chapter (a mean shift); moreover, evolutionary
psychology grew more rapidly since 1992, resulting in a significantly more positive
change-over-time slope (Table 3, Figure 1). In concert, these results suggest that each of
the examined works had a substantial impact on their respective fields. Although both
fields benefited from immediate increases following key publications, this increase was
more sustained for evolutionary psychology than it was for sociobiology.

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Is Evolutionary Psychology Eclipsing Sociobiology?

Figure 1. Raw data and interrupted time-series models for Google Scholar hits (log10 scale)
for “sociobiology” and “evolutionary psychology” by publication year (1960–2003).
10000
Sociobiology (data)
Sociobiology (model)
Evolutionary psychology (data)
1000
Evolutionary psychology (model)
100
10
1
1960
1970
1980
1990
2000
Year of publication
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Is Evolutionary Psychology Eclipsing Sociobiology?

Table 2. Interrupted time-series results for Google Scholar hits for “sociobiology” without
“evolutionary psychology,” 1960–2003.

Variable
b t
pr
Step 1: Mean shift ( 2
R = .977)
Intercept 1.659
61.90**
.99
Linear time (publication year – 1974.5)
0.038
11.80**
.88
Pre-post E. O. Wilson (1975) effect
1.131
13.24**
.90
Step 2: Slope shift ( 2
R = .981)
Intercept 1.760
38.63**
.99
Linear time (publication year – 1974.5)
0.047
10.26**
.85
Pre-post E. O. Wilson (1975) effect
1.014
11.12**
.87
Linear time x pre-post E. O. Wilson (1975) effect
–0.024
–2.65*
–.39

Note. Effects of interest appear in boldface. *p ? .01. **p < .001.

Table 3. Interrupted time-series results for Google Scholar hits for “evolutionary
psychology” without “sociobiology,” 1960–2003.

Variable
b t
pr
Step 1: Mean shift ( 2
R = .920)
Intercept 1.574
30.27**
.98
Linear time (publication year – 1991.5)
0.037
7.29**
.75
Pre-post Tooby and Cosmides (1992) effect
1.050
7.34**
.75
Step 2: Slope shift ( 2
R = .932)
Intercept 1.577
32.52**
.98
Linear time (publication year – 1991.5)
0.051
7.15**
.75
Pre-post Tooby and Cosmides (1992) effect
0.745
4.24**
.56
Linear time x pre-post Tooby and Cosmides (1992) effect
0.021
2.67*
.39

Note. Effects of interest appear in boldface. *p ? .01. **p < .001.

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Is Evolutionary Psychology Eclipsing Sociobiology?

The log-transformed three-year moving average hits for both sociobiology and
evolutionary psychology were submitted to a multiple regression growth curve model that
allowed for linear and quadratic temporal trends (Table 4, Figure 2; see Appendix for
details). First, unsurprisingly, sociobiology received significantly more hits than did
evolutionary psychology at the mean publication year of 1982.5. Second, averaging across
these two related disciplines of evolutionary science, significant linear growth (in log
terms) was observed over time. Third, the linear change-over-time slope was marginally (p
< .10) more positive for sociobiology than it was for evolutionary psychology at the
midpoint of 1982.5. Fourth, and most importantly, the rate of growth (quadratic effect) was
significantly more positive for evolutionary psychology than it was for sociobiology.
Simple effects tests confirmed that, although both sociobiology (b = 0.071, t78 = 26.63, p <
.001, pr = .95) and evolutionary psychology (b = 0.065, t78 = 24.27, p < .001, pr = .94)
showed significant linear growth, sociobiology’s quadratic effect showed deceleration over
time (b = –0.0017, t78 = –6.98, p < .001, pr = –.62), whereas evolutionary psychology’s
exhibited acceleration over time (b = 0.0022, t78 = 9.08, p < .001, pr = .72).


Table 4. Regression results for log10 three-year moving averages of Google Scholar hits as
a function of “sociobiology” (without “evolutionary psychology”) versus “evolutionary
psychology” (without “sociobiology”) and publication year, 1962–2003.


Variable
b
t78
pr
Intercept
1.5176
44.16**
.98
Evolutionary Psychology vs. Sociobiology (EP vs. SB)
1.7429
25.36**
.94
Linear Time (publication year – 1982.5)
0.0680
35.99**
.97
Quadratic Time ([publication year – 1982.5]2)
0.0003
1.49
.17
Linear Time x EP vs. SB
0.0063
1.67†
.19
Quadratic Time x EP vs. SB
–0.0040 –11.36**
–.79
2
Note. R = .96. †p < .10. **p < .001.











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Is Evolutionary Psychology Eclipsing Sociobiology?

Figure 2. Raw data and growth curve regression models for Google Scholar hits (log10
three-year moving average) for “sociobiology” and “evolutionary psychology” by
publication year, 1962–2003.


10000

Sociobiology (data)

Sociobiology (model)

Evolutionary psychology (data)
1000
Evolutionary psychology (model)



100



10



1 1962
1972
1982
1992
2002


Year of publication

The time variable was re-centered by subtracting 2003 from each publication year
and the interaction terms were re-calculated. Simple effects tests revealed that, by 2003,
evolutionary psychology had practically closed the gap with sociobiology, such that the
two were no longer significantly different in terms of Google Scholar hits (b = 0.207, t78 =
1.58, p = .12, pr = .18). Moreover, the simple change-over-time slopes for sociobiology and
evolutionary psychology were significantly different in 2003 (b = –0.156, t78 = –10.55, p <
.001, pr = .77; i.e., the lines tangent to each respective curve at 2003 in Figure 2 were
different). Further tests showed that the simple slope for evolutionary psychology in 2003
was significantly positive (b = 0.157, t78 = 14.98, p < .001, pr = .86), whereas the simple
slope for sociobiology in 2003 was virtually flat (b = 0.00056, t78 = 0.05, p = .96, pr =
.006).
Discussion

So has the term “evolutionary psychology” eclipsed “sociobiology” in the scientific
literature? Although the short answer is “no,” a more accurate answer might be “not yet.”
Although hits for sociobiology continued to grow, its rate of growth over time has been
eclipsed by hits for the newer, related field of evolutionary psychology. Evolutionary
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Is Evolutionary Psychology Eclipsing Sociobiology?

psychology may have an advantage, however, in that it is still a “hot” and occasionally
controversial discipline in the social sciences, whereas sociobiology experienced a similar
growth spur in the late 1970s. Thus, it remains to be seen whether evolutionary psychology
can maintain or even increase its current rate of growth in the future.
Were
Wilson’s
(1975)
Sociobiology and the two Tooby-Cosmides (1992) chapters
from The Adapted Mind truly catalysts that spurred the respective expansions of
sociobiology and evolutionary in the scientific literature? As indicated by the significant
mean shifts, it appears the answer is “yes” for both sets of works. In addition, the Tooby-
Cosmides chapters appear to have been important enough to have also increased the
trajectory of growth over time for evolutionary psychology (a slope shift). Although these
interrupted time-series results show temporal precedence, they cannot rule out possible
spurious, “third-variable” explanations. For example, the heated political controversy
ignited by reactions to Sociobiology may have had the unintended consequence of
increasing its exposure, which may have made Sociobiology a more important work than it
would have been without such controversy (Segerstråle, 2000). Similarly, perhaps in 1992
the time was ripe for an “evolution revolution” in the social sciences, and the Tooby-
Cosmides chapters were more of a consequence of a newfound groundswell of support for
Darwinian ideology rather than a cause of it. Nevertheless, although temporal precedence is
not sufficient to establish causation, it is necessary, and the present findings suggest both
sets of works played definitive roles in the development of their respective fields of
evolutionary science.
One possible limitation of the present research is that Google Scholar is not a
perfect measure of a scientific discipline’s growth over time. For example, journal articles
and other scholarly works are less likely to be catalogued electronically the older they are.
Moreover, because Google Scholar is constantly striving to provide broad, comprehensive
searches of the scientific literature, its searchable database continues to expand. Thus, there
is likely to be some instability in Google Scholar’s hit count. For example, a search
performed in 2008 for “sociobiology” for the 2006 publication year might reveal
substantially more hits than if the same search were preformed in 2007. This instability is
less of a concern for the present study, however, because it is more concerned with relative
hits than absolute hits. Recall that the purpose of this study is one of comparison: (a)
comparing sociobiology to evolutionary psychology and (b) comparisons within each
discipline before and after the publication of an influential work. Because of this
comparative approach, any bias or instability in hit counts is likely to affect both elements
in the comparison equally and in a consistent direction. Moreover, established databases
like PsycINFO suffer from similar limitations when they change which journals they index.
Another potential limitation of the present research is the choice of the log10 metric.
Because of hit counts were log transformed for analyses, linear growth actually reflects
exponential growth over time. Nevertheless, the log transformations were necessary to
avoid violating the normality and homogeneity-of-variance assumptions of regression
because hit counts were extremely positively skewed. Thus, although some loss in
interpretability was incurred by the use of the log metric, this was largely offset by the gain
of adhering to the central tenets of regression.
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Is Evolutionary Psychology Eclipsing Sociobiology?

Overall, the present results suggest that Wilson’s (1975) book and the Tooby-
Cosmides (1992) chapters were truly seminal works that were particularly instrumental in
facilitating the rapid growth of sociobiology and evolutionary psychology, respectively.
Although Feist (2006) and Webster (2007a) suggested that the establishment of journals
play a key role in a scientific field’s development, the present findings suggest that the
publication of an influential book or chapter might be equally important. On a more
specific level, these finding suggest that evolutionary psychology’s influence is now
growing more rapidly than sociobiology, the discipline that helped inspire it. As
demonstrated by a number of empirical studies, evolutionary theory is gaining ground in
psychology textbooks (Cornwell, Palmer, Guinther, and Davis, 2005), the Journal of
Personality and Social Psychology (Webster, 2007b), and neuroscience journals (Webster,
2007c). Some of these gains may be due to evolutionary psychology’s increased focus on
empirical research over the last quarter century (Webster, 2007d). It is hoped that the
present study will not only elucidate the historical emergence of both sociobiology and
evolutionary psychology, but also empirically establish that evolutionary psychology has
grown to the point that it is now at parity with sociobiology in the scientific literature.

Acknowledgements: This material is based upon work supported by the National Institute
of Mental Health under Training Grant Award PHS 2 T32 MH014257 entitled
“Quantitative Methods for Behavioral Research” (to M. Regenwetter, principal
investigator). This research was performed while the author was a postdoctoral trainee in
the Quantitative Methods Program of the Department of Psychology, University of Illinois
at Urbana-Champaign. Any opinions, findings, and conclusions or recommendations
expressed in this article are those of the author and do not necessarily reflect the views of
the National Institute of Mental Health.

Received 12 August 2007; Revision submitted 25 September 2007; Accepted 26
September 2007
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