by Juliana French & Andrea Meltzer

 

140 million. That’s how many women world-wide are estimated to use hormonal contraceptives such as The Pill. The main function of hormonal contraceptives (and a leading reason for why so many women use them) is to decrease the likelihood of conception. But through administering synthetic hormones to achieve protection against unwanted pregnancy, hormonal contraceptives incidentally alter a myriad of other physiological and psychological processes. In a recent paper, we examined the extent to which hormonal contraceptives may alter processes important for maintaining satisfying relationships, such as sexual satisfaction.

Sex is a central feature of adult romantic relationships, which is reasonable considering the adaptive value sex has for reproductive success. It is therefore not surprising that frequent and satisfying sex plays an important role in the maintenance of people’s long-term romantic relationships. Nevertheless, one of the most common side effects of hormonal contraceptives—an evolutionarily novel medical advancement—is decreased sexual desire among women who use them.

Hormonal contraceptives are therefore, by definition, an evolutionary mismatch. A classic, easy-to-digest example of an evolutionary mismatch concerns modern food availability. Humans have an evolved tendency to seek highly caloric foods because this would have been adaptive in our evolutionary history when such foods were scarce. In 2020, however, this evolved tendency may lead you to crave chocolate chip cookies and fast food. When not kept in check, these (once adaptive) cravings contribute to modern rates of obesity. Similar to the abundance of highly caloric foods in our modern environment being mismatched to our evolved psychology, hormonal contraceptives may be mismatched to our evolved relationship processes, explaining, at least in part, some relationship dysfunction such as sexual dissatisfaction.

So, now you may be wondering, “although hormonal contraceptives help to prevent unwanted pregnancy, are they harmful for my relationship?”

Not so fast – there’s more to the story.

A recent study suggests that whether a woman uses a hormonal contraceptive may be less important for her relationship than whether she changes her hormonal contraceptive use after relationship formation. Imagine one woman, for example, who was not using a hormonal contraceptive when she met her partner but decides to start using The Pill after they have been together for a little while (perhaps because she is likely to engage in relatively more frequent sex and doesn’t want to become pregnant). Imagine another woman who was using The Pill when she met her partner but decides to discontinue using hormonal birth control at some point in her relationship (perhaps because she and her partner are trying to become pregnant).

Hormonal contraceptive use that differs from a woman’s use when she met her partner is called hormonal contraceptive incongruency. Notably, many women become hormonal contraceptive incongruent at some point during their ongoing, long-term relationships. Moreover, because many women begin and discontinue hormonal contraceptives multiple times in the course of a relationship, they repeatedly fluctuate between being congruent and incongruent. Are women less sexually satisfied during those times when their hormonal contraceptive use is incongruent (compared to congruent) from their use at relationship formation? This is exactly the question we sought we answer.

We tested whether such within-person changes in hormonal contraceptive use that results in incongruency is associated with decreases in sexual satisfaction. To do this, we asked 203 heterosexual, newlywed wives if they were using a hormonal contraceptive when they began dating their husbands. Then, at the start of their marriages and again every four to six months for up to four years, those wives (a) completed a measure of sexual satisfaction and (b) reported whether they were currently using a hormonal contraceptive. Results demonstrated that wives reported lower sexual satisfaction at times when their hormonal contraceptive use was incongruent with their use at relationship formation compared to times when their hormonal contractive use was congruent with their use at relationship formation.

 

“Wives reported lower sexual satisfaction at times when their hormonal contraceptive use was incongruent with their use at relationship formation”

 

There are two ways to be incongruent with respect to hormonal contraceptive use, however. Whereas some women do not use hormonal contraceptives when they meet their partners and become incongruent when they begin using them, other women use hormonal contraceptives when they meet their partners and become incongruent when they discontinue their use. Is one form of incongruency more strongly tied to decreases in sexual satisfaction than the other? The short answer is, no. In our data, changes in sexual satisfaction that were associated with incongruency did not differ for wives who were incongruent by “starting” hormonal contraceptives after relationship formation versus those who were incongruent by “discontinuing” hormonal contraceptives after relationship formation.

These findings suggest that simply using a hormonal contraceptive may not necessarily increase one’s risk of experiencing sexual dissatisfaction in a relationship. Rather, it is hormonal contraceptive incongruency—either beginning or discontinuing the use of hormonal contraceptives after relationship formation—that seems to be associated with future sexual problems.

This work represents an important methodological advancement for research examining the implications of hormonal contraceptive for romantic relationship processes. Although others have previously demonstrated associations between hormonal contraceptive incongruency and relationship processes (for example, relationship satisfaction and jealousy), this paper is the first to do so using a longitudinal design and within-person analyses. Cross-sectional studies have sometimes failed to detect between-person effects of hormonal contraceptive incongruency, and—indeed—when we examined our data using between-person analyses at baseline we also did not detect differences in sexual satisfaction between women who were congruent versus incongruent. Crucially, the longitudinal method and corresponding analyses that we conducted in this paper enabled us to statistically separate those non-significant between-person differences in incongruency from the key significant within-person changes in incongruency that are central to the underlying phenomenon.

We see this as a fruitful starting point for many future research questions. For example, is changing your type of hormonal contraceptive—perhaps by either switching from one brand of The Pill to a different brand or to a different hormonal method such as The Patch—also a form of incongruency? And, if so, are these other potential forms of incongruency also detrimental to relationships?

Without having the longitudinal data to answer these questions, we can only speculate. It seems probable that, yes, there are likely multiple forms of hormonal contraceptive congruency. But the extent to which other forms of incongruency may impact relationship outcomes, such as sexual satisfaction, likely depends on how different the incongruency-related changes actually are. That is, changing from a progestin-only pill to a different progestin-only pill is less of an incongruency than changing from a progestin-only pill to a combination (estrogen and progestin) pill, and the latter is still less of an incongruency than discontinuing hormonal contraceptives altogether.

When women discuss birth control options with their medical doctors, the conversation often revolves around common side effects, such as weight gain, headaches, mood changes, and decreased libido (to name a few). Relational side effects that may occur as a result of changes in hormonal contraceptive use, such as decreases in sexual satisfaction, are less-often (if ever) considered or discussed. There are many factors that contribute to sexual satisfaction—for example, how attracted you are to your partner (which, by the way, hormonal contraceptives may also alter)—and our recent research suggests that hormonal contraceptive incongruency is one such factor. Given the adaptive significance of long-term relationships for humans, it is paramount to understand how modern novelties such as hormonal contraceptives can impact relationship processes and stability.

 

 

Read the paper: The implications of changing hormonal contraceptive use after relationship formation

The HBES Executive Council is now soliciting funding applications from HBES members for an October 1, 2020 deadline.

 

Two grants are available for this round of funding:

1. General Funding Grant, which is intended to subsidize costs associated with hosting events such as conferences and pre-conference meetings, workshops, and other activities or educational opportunities related to the mission of HBES.

Not an HBES member? Join or renew today!

by Jaimie Arona Krems & Daniel Conroy-Beam with thanks to Laureon A. Merrie

 

Lenù & Lila, Gene & Phineas, Thelma & Louise, Cap & Bucky. Best friends are fixtures in our lives. Best friends might not benefit our fitness as obviously and directly as mates do, but having good friends is thought to be the next best thing for one’s health behind quitting smoking. In a recent paper, we ask how the mind might integrate our myriad friend preferences—for friends who are smart like Lenù, charismatic like Phineas, steadfast like Thelma or Cap—to make actual friend choices.

Perhaps in an ideal world, everyone we liked would like us back, time and affection would be infinite, and everyone we’ve ever encountered (and liked) we could maintain as friends. But as nice as ideal worlds and adages about the unbounded nature of love can sound, they bump up against reality. For example, time is inelastic yet required to maintain social relationships. To some extent, our affections might also be finite. In the end, we can maintain only so many ties at any one time.

Somehow, then, we must evaluate, compare, and ultimately select friends. Considering how important having friends and their support can be for one’s survival—and potentially even the thriving of one’s offspring—these friend choices matter.

To make these choices, we need an algorithm that combines information about what we prefer in friends, and the extent to which each prospective friend fulfills those friend preferences, presumably translating this information into a summary rating of sorts. There are a number of “preference integration” algorithms that could accomplish this.

In the mating literature, a Euclidean integration hypothesis has performed quite well. Therein, the Euclidean algorithm represents mate preferences and prospective mates as points within an n-dimensional space, computing a summary mate value that is inversely proportional to the distance between those points. For example, this summary can integrate the discrepancies between wanting a friend who’s a 10/10 in loyalty, a 10/10 on intelligence, a 4/10 on optimism, and so on, with a prospective friend who is a 6/10 on loyalty and intelligence and an 8/10 on optimism.

We tested whether some of those critical predictions derived from a Euclidean integration hypothesis—which have already found support in the mating literature—hold in the friendship domain. To do this, we gathered data from three separate samples of US participants (N = 817 undergraduate and adult community participant convenience samples). In each sample, we asked participants to rate themselves on 23 trait characteristics using 8-point bipolar scales. For example, we’d ask people to rate themselves as being “Very loyal” to “Very disloyal”. Participants also completed ratings for both their ideal same-sex best friends and their actual same-sex best friends. They also repeated this for their ideal and actual same-sex close friends and for their ideal and actual (or most recent) romantic partners.

We then computed several dimensions of partner value, including the friend and mate values of each participant, as well as the extent to which each participant’s actual best friends (and close friends, mates) fulfilled their ideals. For example, a person’s best-friend preference fulfillment was calculated as the Euclidean distance between the preferences they marked having in a best friend and where they marked their actual best friends as falling on those trait characteristics.

Using these data, we found support for several critical predictions implied by a Euclidean integration hypothesis in the friendship domain. First, we predicted that people who possess characteristics that render them ideal friends (i.e., people with high friend value) should be highly sought after, meaning that they have their pick of friends. Thus, we predicted—and found—that high friend-value individuals seem able to attract friends who better fulfill their preferences. We also predicted and found that high friend-value individuals not only set higher standards for ideal friends—after all, they would seem able to make such demands—but also that they report having real-world best friends who themselves have higher friend-value. In addition, we also explored these patterns with respect to people’s mate value, mate preferences, and mate preference fulfillment—replicating Conroy-Beam and colleagues’ previous research.

 

“We also predicted and found that high friend-value individuals not only set higher standards for ideal friends, but also that they report having real-world best friends who themselves have higher friend-value”

 

We also started to explore something new: the dissociability of friend- and mate-value. On one hand, the characteristics that make one an ideal friend (e.g., being nice) can overlap with the characteristics that make one an ideal mate (e.g., being nice). At the same time, people might also have some different preferences for prospective friends and mates. A same-sex friend who is highly sexually attractive might be a threatening rival in the mating domain, for example, but an other-sex mate who is highly sexually attractive might be rather desirable.

So, do people’s friend values better predict their friend outcomes (than mate outcomes), and do people’s mate values better predict their mate outcomes (than friend outcomes)?

Sort of.

We find some, albeit mixed, support for dissociability. This finding is particularly intriguing, though, insofar as it adds to the broader conversation about association value (see Michael Bang Petersen, Aaron Sell, John Tooby, and Leda Cosmides’ 2012 paper in this same journal for more on that).

A large part of the impetus for our work was to address the gap in friendship research. To some extent, these important relationships remain an evolutionary mystery. More work on friendships could contribute to solving that puzzle. Luckily, a pretty handy playbook for conducting some future work on friendship already exists—the robust, deep literature on mating relationships.

Here, drawing from work conducted in the mate preferences literature, we found some support for the Euclidean integration hypothesis, suggesting that this algorithm might be how the mind integrates friend preferences to make friend choices. However, exciting new work recently accepted at EHB also suggests another algorithm to explore in friendships (see Bradner, Brase, & Huxman, in press). We look forward to pleasantly arguing with our friends about this, and to the future of work on friendship in evolutionary social science.

 

 

Read the paper: First tests of Euclidean preference integration in friendship: Euclidean friend value and power of choice on the friend market

by Brendan Zietsch

 

Life history theory has been promoted as a unifying framework for understanding trait covariation in the social sciences. Underlying this approach is the assumption that patterns of trait covariation across species, and the Darwinian principles thought to underlie those patterns, can be extrapolated to trait covariation across individuals within human populations. In particular, it is assumed that a ‘fast-slow’ continuum of life history ‘strategies’, observed across species, should be observed across individuals within human populations – not only with regard to traditional life history traits but practically all individual differences, including personality and psychopathology.

In my paper with Morgan Sidari we argue that these assumptions are not justified. The processes that create trait covariation across species and across individuals are fundamentally different, and so the two types of covariation need not be parallel or even related. This fundamental problem undermines a great deal of research in this burgeoning field, and warrants a rethink moving forward.

To illustrate the point, we use the simple example of body height. Humans are taller than rabbits because of their different genes. Individual humans also differ in height largely because of their different genes. But the processes that create genetic height differences between rabbits and humans (i.e. Darwinian evolution) are nothing like the processes that create genetic height differences between individual humans. The fact I am taller than a rabbit is primarily due to our different histories of Darwinian evolution over countless generations of different selective pressures; the fact I am taller than my friend or my brother has little (or nothing, in the case of my brother) to do with our different histories of Darwinian evolution, but rather my chance inheritance of more “tall alleles” compared to them. As with all individuals of European ancestry, many of my friends and I share nearly the same set of ancestors who were alive 1,000 years ago (and likely many ancestors more recent than that) – a very short period in evolutionary time. Therefore, the reason my friends and I are of different heights is largely independent of our different histories of Darwinian evolution. We are different heights mostly for the same reason my brother and I (who share all our ancestors) are of different heights – that is, the random shuffling process of Mendelian segregation during meiosis gave us different combinations of our ancestors’ genetic material. Overall, this example highlights why we cannot straightforwardly transfer the same evolutionary principles from the explanation of human-rabbit differences to human-human differences.

 

“Darwinian phenotype-environment matching at the species level and plasticity at the individual level are completely different processes and may or may not lead to equivalent predictions regarding trait covariation.”

 

The same argument applies to trait covariation. If environments that tend to favour large bodies also tend to favour high parental investment, then genes controlling the two traits will come to covary across species. There is no equivalent evolutionary process creating trait covariation across individuals. Selection and evolution can lead to phenotypic plasticity and adaptive calibration of individuals’ traits to their personal environments; but Darwinian phenotype-environment matching at the species level and plasticity at the individual level are completely different processes and may or may not lead to equivalent predictions regarding trait covariation. Similarly, there are different consequences at the species and individual levels in situations where selection on one trait depends on the level of another trait. If genes for high parental investment are advantageous in a large species and disadvantageous in a small species, genes for large body size and genes for high parental investment will tend to go together across species, and likewise genes for small body size and low parental investment. But there is no equivalent evolutionary process by which variation in different traits within a population can be combined based on how well they work together. Darwinian evolution cannot combine “tall alleles” with “high parental investment alleles”, and “short alleles” with “low parental investment alleles”, within a sexually reproducing population in the same way as it can across species, because of Mendel’s Law of Independent Assortment: segregating alleles are transmitted to offspring independently of each other, so allele configurations are not inherited.

We explain why exceptions to Mendel’s Law of Independent Assortment – correlational selection, physical linkage, non-random mating, and pleiotropy – don’t change our central point. We also discuss adapted developmental plasticity, where variation and covariation of life history-related traits is shaped by environmental conditions during an individual’s development. In particular, we note behavioural genetics research that shows little influence of early environment on trait variation and covariation, and why these findings pose problems for these plasticity-based life history accounts. Further, we discuss why proposed trade-offs between specific life history traits – trade-offs that are typically on the within-individual level – need not translate to covariation of those traits across individuals.

 

“Much of the life history work on trait covariation in humans does not have a solid theoretical grounding; there is little basis for the fast-slow continuum as a framework for understanding human trait covariation.”

 

Overall, we conclude that much of the life history work on trait covariation in humans does not have a solid theoretical grounding. In particular, there is little basis for the fast-slow continuum as a framework for understanding human trait covariation. Given the frequent attacks on evolutionary psychology from other disciplines, our field must be especially vigilant for conceptual flaws in the underpinnings of our research – otherwise, we risk validating those criticisms. Those using life history theory to study individual differences and trait correlations must ensure their paradigm is properly connected to the fundamentals of evolutionary theory.

 

 

Read the paper: A critique of life history approaches to human trait covariation

by Oliver Sng, Keelah Williams, & Steven Neuberg

 

The study of sex and age stereotypes—the general beliefs we hold about others based on their sex and age—has had a long history. In a recent paper, we present a new perspective to thinking about this topic. Specifically, we propose that social perceivers are actually “lay adaptationists”. In other words, although lay perceivers are not aware of formal evolutionary theories (e.g., parental investment, life history), they nonetheless pick up on and generate predictions about how others’ sex and age influence their goals and behaviors.

From this perspective, perceivers categorize and stereotype others by sex and age, because another person’s sex and age are associated with their goals (e.g., learning, mating, parenting), which in turn are associated with distinct opportunities and threats they might pose (e.g., potential mates, potential mate competition). This generates several insights.

First, it is not sufficient for perceivers to be categorizing others in terms of just sex, or just age. This is because goals vary by the interactive combinations of sex and age (e.g., men are more oriented towards short-term mating goals than women are, but especially so at younger ages). To usefully represent distinct social opportunities and threats, perceivers should categorize others in terms of the combination of others’ sex and age.

Indeed, they do so. Using a memory recall paradigm often referred to as “who-said-what”, we find that perceivers are more likely to confuse individuals of the same sex or of the same age group (e.g., confusing women with other women instead of men, confusing 60 year-olds with other 60 year-olds instead of 20 year-olds). More important, they are especially likely to confuse individuals of the same sex and age (e.g., confusing 20-year-old women with other 20-year-old women instead of 60-year-old women or 20- and 60-year-old men). Hence, perceivers mentally group others not by sex or age independently, but by the interaction of both.

The same principle should apply to stereotypes—beliefs about how women and men of different ages are like. Indeed, in another set of studies, we find that too. For example, perceivers believe that men are more oriented towards seeking short-term partners than women are, but this sex stereotype is stronger for stereotypes of younger (e.g., 28-year-olds) than older individuals (60-year-olds). The reverse is observed for stereotypes of long-term mating orientation. Young women (e.g., 28-year-olds) are stereotyped to be more oriented towards seeking and maintaining long-term relationships than young men, but this stereotype disappears for stereotypes of older individuals (e.g., 60-year-olds). Hence, perceivers also hold interactive sex and age stereotypes.

Finally, the current perspective also has implications for thinking about certain widely studied sex stereotypes. A considerable literature has accumulated on sex stereotypes of agency and communion. Agency comprises traits that focus on self-assertion, such as being independent and competitive. Communion comprises traits that maintain harmonious social relationships, such as being caring and understanding.

Why are men typically stereotyped as more agentic than women? One explanation may be because men are stereotyped as more oriented than women towards short-term mating goals (as just mentioned above), and the pursuit of short-term mating goals likely requires more agentic behavior, such as competitiveness and dominance. If the sex stereotype of agency is indeed derived from sex stereotypes of short-term mating goals, then presenting perceivers with direct information that both men and women are similarly oriented towards seeking short-term mates should eliminate the sex stereotype of agency.

“Providing perceivers with direct information about the adaptive goals (e.g., mating, parenting) that male and female targets are engaging in seems to override prominent sex stereotypes of agency and communion.”

Indeed, that is the case. Perceivers presented with a male or female target, without any additional information, stereotype the man as more agentic than the woman. However, when perceivers are given information that a woman and a man are similarly spending time looking for short-term partners, the woman and man are stereotyped as equally and highly agentic.

A similar logic could be applied to thinking about sex stereotypes of communion. Why are women stereotyped to be more communal than men? One explanation is that the sex stereotype of communion may be derived from sex stereotypes of long-term mating goals (of women as being more oriented towards such goals than men), because seeking and maintaining long-term mating relationships requires communal traits such as kindness and care. If this is so, then perceivers presented with men and women who are similarly engaging in long-term mating goals should be viewed as similarly communal.

This prediction is borne out, too. In the absence of additional information, perceivers stereotype a female target as more communal than a male target, consistent with the stereotype. However, when told that both targets have and spend time with a long-term relationship partner, the male and female targets are viewed as equally communal

In general, providing perceivers with direct information about the adaptive goals (e.g., mating, parenting) that male and female targets are engaging in seems to override prominent sex stereotypes of agency and communion. Prominent sex stereotypes appear to emerge from people’s stereotypes about sex and age differences in the relative prominence of adaptive goals.

To summarize, perceivers categorize and stereotype by the interactional combination of others’ sex and age, and these stereotypes suggest that perceivers are lay adaptationists in certain ways. For instance, just as parental investment theory predicts that males in our species are more likely to invest in mating effort than women are, lay perceivers also “predict”, through sex and age stereotypes, that men (and particularly young men) are more oriented than women towards short-term mating goals and behaviors. These adaptive goal stereotypes may in turn underpin other stereotypes, such as sex stereotypes of agency and communion.

The findings outlined above may seem intuitive, and intuitive findings are sometimes devalued. But that the findings seem intuitive to you as a reader is itself something the perspective would predict, simply because you are also a lay adaptationist (and likely also a professional adaptationist!). In other words, you are likely also using the sex and age of others, interactively, to predict their goals and behavior. Hearing that people categorize and stereotype by sex and age in these particular ways should therefore be unsurprising.

The idea that perceivers may be lay adaptationists is useful beyond enhancing our understanding of the social perception of sex and age. In other work, we apply a similar approach for better understanding race stereotyping. Specifically, certain stereotypes of Black and White Americans may not be about race, per se, but instead may reflect what we call ecology stereotypes—beliefs about the traits of individuals who live in more versus less harsh and unpredictable ecologies. Supporting this, we have found that providing perceivers with direct information about a Black or White individual’s home ecology can override race stereotypes of traits such as impulsivity and aggressiveness.

Thinking about perceivers as lay adaptationists lends a new way of thinking about social perception and stereotyping. Stereotyping, in particular, is traditionally presented as an outcome of “lazy” minds trying to simplify the world. The current work presents a more nuanced picture. Social perceivers are sensitive to the interactions of sex and age in thinking about and predicting the traits of others. When making social inferences about agency and communion, perceivers also prioritize information about an individual’s relevant goals, over the general category an individual belongs to. Indeed, our stereotypes may be more strategic than typically thought.

 

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Read the paper: Sex-age stereotyping: Social perceivers as lay adaptationists