Research Projects
Human Courtship
Adaptations:
Nonhuman vertebrate species express biological adaptations that
facilitate courtship and mate competition. In males of most sexually
reproducing species, for instance, individuals exhibit a type of
"mating response" when they encounter potential mates: species-specific
courtship behaviors, combined with rapid increases in testosterone and
corticosterone. These responses, furthermore, are regulated by
structures within a specific limbic-hypothalamic circuit, such as the
medial preoptic area. The phylogenetic conservation of this circuit in
turn raises the possibility that humans express similar (homologous)
mechanisms. Our lab has an ongoing research program testing whether in
fact human males also exhibit a mating response similar to that seen in
nonhuman vertebrates. Four published studies have now provided evidence
that men exhibit reactive testosterone increases after brief social
interactions with young women, for instance, and three studies have
provided evidence for reactive increases in cortisol as well:
Roney, J. R., Mahler, S. V., & Maestripieri, D. (2003).
Behavioral and hormonal responses of men to brief interactions with
women. Evolution and Human Behavior, 24, 365-375.
Roney, J. R., Lukaszewski, A. W., & Simmons, Z. L. (2007). Rapid
endocrine responses of young men to social interactions with young
women. Hormones and Behavior, 52, 326-333.
Roney, J. R., Simmons, Z. L., & Lukaszewski, A. W. (2010).
Androgen receptor gene sequence and basal cortisol concentrations
predict men's hormonal responses to potential mates. Proceedings of
the Royal Society of London B, 277, 57-63.
In addition to investigating hormonal responses to potential mates,
an early study also demonstrated that mere exposure to young women can
nonconsciously prime psychological changes in men that appear designed
to promote more attractive self-presentations to potential mates:
Roney, J. R. (2003). Effects of visual exposure to the opposite sex:
Cognitive aspects of mate attraction in human males. Personality
and Social Psychology Bulletin, 29, 393-404.
Our ongoing investigations are designed to extend this research in
various ways. A current set of experiments being directed by Zach
Simmons for his dissertation are investigating the possible functions
of rapid, transient increases in testosterone. A major function of
testosterone appears to be the regulation of energy investment into
either mating or survival effort (broadly construed), with higher
testosterone generally associated with greater relative investment in
mating effort, and greater demands on survival effort associated with
decreases in testosterone. In theory, for example, testosterone should
decrease during immune activation in order to allow more energy to be
allocated to the immune response, and one paper from our lab
contributed evidence for this effect in humans:
Simmons, Z. L., & Roney, J. R. (2009). Androgens and energy
allocation: Quasi-experimental evidence for effects of influenza
vaccination on men's testosterone. American Journal of Human Biology,
21, 133-135.
Transient increases in testosterone seen after exposure to potential
mates may provide a signal regarding the immediate importance of
investment in mating effort that serves to calibrate psychological
mechanisms toward mate competition in the relative short-run, much as
higher basal production of testosterone may allocate energy resources
into mating effort (e.g., into the construction of muscle mass) over
longer time scales. This psychological calibration toward mate
competition may include outcomes such as lower risk-aversion, greater
competitiveness, and greater willingness to approach potential mates,
all of which are being tested in the ongoing research.
The Role of Ovarian Hormones in Women's
Mating Psychology:
An intriguing recent body of research has provided
evidence that aspects of women's mating psychology undergo changes
associated with phases of the menstrual cycle. Preferences for more
masculine features in men (e.g., faces, voices, bodies), for
instance, are stronger when women are tested near ovulation than when
tested during other phases of the cycle. The most prominent proposed
explanation for these cycle phase shifts is that they are part of a
specially designed "mixed" mating strategy in which women prefer to
form pair-bonds with high investing men who are good fathers but also
opportunistically commit infidelities near ovulation in order to obtain
higher quality genes than may be available from their long-term
partners. On this account, masculine features index aspects of
heritable fitness, and women exhibit relatively stronger preferences
for these traits specifically during fertile days of the cycle, since
only on these days can the genetic benefits of infidelities outweigh
the risks associated with extra-pair sex.
Our lab is testing an alternative functional explanation for cycle
phase shifts in mate preferences. This explanation proposes that these
shifts are essentially the products of mechanisms that allocate
attention and motivation differentially depending on the most important
adaptive problems currently being faced by an individual. During long
stretches of infertility associated with events like lactation or
energy shortage, it may have been functional for ancestral women to
down-regulate attention to men's sexual attractiveness in order to
focus on more pressing current problems, but to up-regulate such
attention in the more rare cycles in which fertility returned. If,
furthermore, a hormone like estrogen (known to be higher in more
fertile cycles) is the physiological signal regulating these shifts,
then a mechanism designed primarily to shift attention and motivation
between different cycles might also produce small within-cycle shifts
as a by-product of its design, since estrogen peaks near ovulation
within cycles. Further discussion of this theory can be found in:
Roney, J. R. (2009). The role of sex hormones in the initiation of
human mating relationships. In P. T. Ellison & P. B. Gray (Eds.), The
endocrinology of social relationships (pp. 246-269). Cambridge,
MA: Harvard University Press.
Empirical tests of the physiological signals that regulate cycle phase
shifts in attractiveness judgments can help provide evidence regarding
the alternative functional theories. Estrogen, for example, typically
exhibits a within-cycle peak near ovulation, but also often a secondary
peak in the luteal phase when conception is not possible. If
preferences for masculinized traits track estrogen fluctuations not
only near ovulation but also into the luteal phase, this pattern would
be consistent with a between-cycle mechanism that adjusts psychology
according to cycle fertility but less consistent with a specialized
infidelity-promoting mechanism that if well-designed should tightly
couple preference shifts to days of the cycle when conception is
possible. Three studies from our lab have provided evidence that
preferences for some androgen-dependent traits do in fact track
estrogen fluctuations across the cycle, including past ovulation and
into the luteal phase:
Roney, J. R., & Simmons, Z. L. (2008). Women's estradiol
predicts preference for facial cues of men's testosterone. Hormones
and Behavior, 53, 14-19.
Lukaszewski, A.W., & Roney, J. R. (2009). Estimated hormones
predict women's mate preferences for dominant personality traits. Personality
and Individual Differences, 47, 191-196.
Roney, J. R., Simmons, Z. L., & Gray, P. B. (2011). Changes in
estradiol predict within-women shifts in attraction to facial cues of
men's testosterone. Psychoneuroendocrinology, 36,
742-749.
One limitation of the above studies is that they involved only 1-2 data
points per woman, and much more detailed information could in principle
be obtained by following the same women across more days of their
respective cycles. Our ongoing research is doing just that: daily
saliva samples, daily diaries, and multiple stimulus rating lab
sessions per woman subject are being collected and analyzed in a
current study.
The Functional Origins of Personality and
Individual Differences:
Why do people differ in their personalities? In other
traits? A prominent idea in the current literature is that genetic
differences explain much of the relevant variation: people differ in
extraversion, for instance, because some people have genes for
extraversion and some genes for introversion. An alternative idea,
however, is that personality traits may be adjusted in functional ways
depending on feedback received over the course of development. As part
of his dissertation, Aaron Lukaszewski applied this "facultative
calibration" hypothesis to the explanation of individual differences in
extraversion. Based on the expectation that extraverted behavioral
strategies would likely have had higher payoffs for stronger and more
physically attractive individuals across most of human history, this
research tested and confirmed the hypotheses that strength and
attractiveness are positively correlated with self-reported levels of
extraversion. The relevant studies have recently been published:
Lukaszewski, A. W., & Roney, J. R. (2011). The origins of
extraversion: Joint effects of facultative calibration and genetic
polymorphism. Personality and Social Psychology Bulletin, 37,
409-421.
The above paper also found that the effects of strength and
attractiveness in men were statistically independent of variance in
extraversion explained by an androgen receptor gene polymorphism,
despite the fact that variation in this gene was significantly
correlated with both strength and extraversion. That result argues for
the simultaneous effects of facultative calibration and genetic
polymorphism, suggesting the importance of both in explaining the
origins of personality.
The androgen receptor gene is of broader interest to our lab because of
its potential to explain individual differences associated with mating
psychology. Shorter numbers of CAG repeats in this gene are essentially
associated with more active androgen receptors. Since androgen
receptors are expressed widely throughout the brain and body, adjusting
their activity via this one gene can potentially alter the degree of
androgenicity throughout the entire organism. Because androgens appear
to regulate relative investment in mating (vs. survival) effort,
shorter CAG repeat lengths in this gene may predict trait-like
individual differences in variables associated with mating effort.
Consistent with this, one paper from our lab demonstrated that men with
shorter repeat lengths exhibited larger testosterone responses to
interactions with potential mates:
Roney, J. R., Simmons, Z. L., & Lukaszewski, A. W. (2010).
Androgen receptor gene sequence and basal cortisol concentrations
predict men's hormonal responses to potential mates. Proceedings of
the Royal Society of London B, 277, 57-63.
A follow-up paper has reported significant associations between CAG
repeat length and variables associated with intrasexual competitiveness
in men (physical strength and self-reported levels of dominance
and prestige):
Simmons, Z. L., & Roney, J. R. (2011). Variation in CAG
repeat length of the androgen receptor gene predicts variables
associated with intrasexual competitiveness in human males. Hormones and Behavior, 60, 306-312.
Miscellaneous
Research Projects:
A few other lines of research are also ongoing in our lab, which
we hope to expand upon in the near future. First, we are interested in
the information that observers are able to obtain from human faces.
Previous research has shown that women exhibit stronger preferences for
more masculine male faces when the women are tested near ovulation than
when tested in other regions of the cycle. Masculinity in these studies
has been interpreted as an index of both genetic and paternal quality:
a positive indicator of genetic quality via its presumed association
with higher testosterone, and a negative predictor of paternal quality
based on studies showing that observers rate masculinized faces lower
on perceived prosocial traits. In an initial study from our lab, we
sought to test whether female observers were in fact accurate in their
subjective impressions of male faces. We found that women's ratings of
men's facial masculinity were positively correlated with the
testosterone concentrations of the men depicted in the face
photographs. Likewise, women's ratings of how much the men like
children (from facial photos alone) were significantly and positively
correlated with the men's scores on an interest in infants test. These
findings are published in:
Roney, J. R., Hanson, K. N., Durante, K. M., & Maestripieri, D.
(2006). Reading men's faces: women's mate attractiveness judgments
track men's testosterone and interest in infants. Proceedings of
the Royal Society of London B, 273, 2169-2175.
A number of investigations are ongoing as follow-ups to this paper,
including cross-cultural investigations of rating accuracy, and studies
attempting to identify the specific perceptual cues that may best index
endocrine and attitudinal variables.
A second line of research is investigating new approaches to the study
of human mate preferences. The mate preference literature has been
largely dominated by self-report methodologies in which subjects simply
rate or rank lists of traits for their importance in a potential mate.
A common finding in this literature is that people prefer kindness and
trustworthiness above all other traits in a possible partner, and
generally rate traits like dominance as much lower in importance. In
one study from our lab, though, we questioned whether these preferences
depend on the targets of a partner's behavioral acts: that is, do
people prefer that a partner be extremely kind specifically toward
themselves, or toward other people in general? The results demonstrated
that subjects exhibit preferences for extremely high levels of kindness
and trustworthiness only when considering behaviors directed toward
themselves or their friends/family, and shift to lower preferences for
these traits (and higher preference for dominance) when considering a
partner's behavior directed toward other classes of individuals. These
findings are published in:
Lukaszewski, A. W., & Roney, J. R. (2010). Kind toward whom?
Mate preferences for personality traits are target specific. Evolution
and Human Behavior, 31, 29-38.
Finally, other ongoing studies are attempting to develop new methods of
assessing mate preferences that do not rely entirely on self-report and
its associated problems with respect to whether subjects have accurate,
consciously accessible insight into the traits that generate feelings
of attraction toward others. One approach
involves policy-capturing
methodologies that use ratings of perceptual stimuli in lieu of ratings
of
trait importance, for example, and we are currently in the process of
preparing paper submissions based on the results of such studies.