I briefly describe several programmatic lines of research below in which I have been involved, and in which I am currently involved. For each program of research, I highlight a few key results. Other lines of research, not mentioned below, are notable from the published, under review, and in preparation manuscripts detailed on my vitae. My research over the past several years has had the overarching goal of gaining a clearer and more comprehensive understanding of human family psychology and behavior expanding on research in cognitive psychology, social/personality psychology, evolutionary psychology, and developmental psychology. A special focus of my research has been on differential parental treatment of offspring and psychological and behavioral differences as a function of birth order. Many of the lines of research I am interested in bridge gaps between traditional psychological fields and the field of evolutionary psychology. Undergraduate students have played an integral role in these research areas. They have been involved in developing surveys, collecting data, entering data, cleaning data, and analyzing data. Undergraduate students have been and will continue to be involved in my research.
My colleagues and I have conducted a series of studies designed to identify birth order differences in personality. In one study (Michalski & Shackelford, 2002), my co-author and I tested several claims made by Sulloway (1996). In addition, we analyzed separately birth order differences for sibships comprising full siblings and sibships comprising half or step siblings. In these separate analyses, we discovered a somewhat different pattern. Previous claims had stated that laterborns should score higher on Openness/Intellect. Contrary to this claim, we discovered that firstborns from mixed sibships score significantly higher on Openness/Intellect than laterborns. This finding suggests that firstborns are forced to seek out alternative niches when parental investment favors younger siblings who share a genetic link with the firstborn's stepfather. These analyses are the first to examine birth order differences separately for full and mixed sibships and suggest that future research could profitably explore the impact of genetic relatedness between siblings on later psychological characteristics. I have pursued this research possibility further in several other studies and papers that are currently in preparation. My advisor and I also examined the relationships between birth order and sexual strategies (Michalski & Shackelford, 2002). In this study, we examined whether laterborns, relative to firstborns, are more likely to pursue a short-term sexual strategy. We tested several hypotheses and found support for only one. We found that laterborns report a desire for a greater number of sexual partners over several intervals in the future. These results, while largely not supporting the hypotheses, have provided an interesting avenue of future pursuit. It appears that a differentiation must be made between actual and desired sexual strategy. In conjunction with a colleague in Canada, I have attempted to replicate these findings with additional measures differentiating between actual and desired sexual strategies and with a larger sample.
My colleagues and I have recently completed a study of over 700 college students. In this study, we secured assessments of conflict between siblings. Some evolutionary psychologists have claimed that conflict should be greater between step and half siblings than among full siblings. We tested this claim and did not find support for this hypothesis. Instead, we predicted, because full siblings are competing over resources from the same parents, that conflict should actually be higher among full siblings than among half or step siblings. Additionally, we secured from participants assessments of conflict with siblings while they were growing up and currently. We found that reported conflict levels decrease over time for full and half siblings. For step siblings we found that conflict increases over time. This research further suggests that an understanding of sibling relationships from an evolutionary perspective can be used successfully to identify how genetic relatedness results in differing strategies used by siblings. Assessing the evolved psychology of siblings designed to produce skepticism of a full genetic relationship with putative full siblings is one avenue of research I would like to pursue. My interests in sibling conflict forced me to seek out measures of conflict including sources of conflict and rates of conflict. I was interested in examining which types of conflict change throughout childhood. I soon found that no such inventory existed. I proceeded to collect pilot data and have constructed an inventory including over 50 sources of conflict in sibling relationships. I will continue research on this inventory and examine its psychometric properties in follow-up studies. This inventory is critical for me to conduct future research. With this inventory, I will be able to examine changes in conflict across childhood, whether certain types of conflicts change more for full siblings, half siblings, or stepsiblings, and whether conflict motivates differential niche-seeking behaviors among siblings.
My colleagues and I recently examined the claim that parents favor firstborn and lastborn offspring. We tested this hypothesis through the use of reports secured by participants about themselves and their siblings. We found that firstborns and lastborns both report biases that favor them. Middleborns do not show this bias. Middleborns were equally likely to report that their parents favored either a firstborn, middleborn, or lastborn. We then looked at the reported birth order of the parent's favorites by the birth order of the respondent. The results reveal that both firstborns and middleborns report parental favorites as being either firstborn or middleborn, respectively. A different pattern emerges for lastborns. Lastborns report that firstborns and lastborns are more likely to be reported as parental favorites. This finding is consistent with previous research on parental favoritism whereas the findings for firstborns and middleborns are not. The results of this study highlight parental favoritism biases in favor of firstborn and lastborn siblings and highlight the need to understand parental favoritism from the perspective of siblings rather than from parents. Future research could profit by further exploring how members of the same family differentially perceive investment. A future line of research that I am interested in pursuing is on how parents may disguise their investment biases in one particular child from their other children and how mothers and fathers may differ in how they may accomplish this.
In a particularly productive line of research, I investigated several dimensions of the psychology of familial investment as a function of perceived similarity between family members (Michalski & Shackelford, 2004). The different adaptive problems faced by men and women over evolutionary history led evolutionary psychologists to hypothesize sex differences in grandparental investment and the use of resemblance as a proxy for a genetic relationship. Paternal grandfathers have two links of potentially severed genetic relatedness between themselves and their grandchildren and should thus report the less investment than other grandparents. Maternal grandmothers have no such links of cuckoldry between themselves and their grandchildren and should thus report the greater investment in their grandchildren than other grandparents. Maternal grandfathers and paternal grandmothers each have one link of potential cuckoldry between themselves and their grandchildren and their investment is predicted to be intermediate between paternal grandfathers and maternal grandmothers. Evolutionary psychologists have predicted that paternal grandfathers should bias investment more than other grandparents based on perceived resemblance between themselves and their grandchildren. We tested this claim and attempted to replicate several findings from previous studies using a sample of older adults (N = 207). We found that
These findings were interesting for the support of several key hypotheses, but the failed test of the hypothesis concerning the use of similarity as a proxy for investment was even more interesting to me. I would like to pursue this line of research further with older adults and target more precisely the strategies parents may use to secure investment for their children from their parents. Grandparents may respond to cues of resemblance between their grandchildren and parental generation rather than to resemblances between themselves and their grandchildren and parents may employ a strategy to claim resemblances between their offspring and parents.
Another new and already productive line of research is one designed to gain a clearer understanding of the predictors of parental investment. Some previous research has suggested that fathers use resemblance as a proxy for their investment and mothers stress resemblance between their offspring and putative fathers. I have collected preliminary data that supports the idea that a paternal favorite is, more often than chance, the offspring who also most resembles the father. I am following up on this line of research in a study that examines various factors of parental investment as a function of psychological and physical resemblance to offspring. Several colleagues have agreed to collect data at their universities. I have completed a grant proposal that rigorously examines these issues in samples of biological parents and their offspring and among stepparents and their stepchildren. Prior to beginning this area of research, I reviewed the literature for inventories on parental investment and was surprised to find no extant inventory that directly assessed the variables of interest to me. I began pilot work to develop an inventory and found out that a colleague had developed such an inventory but had not yet published the inventory. In conjunction with my advisor, I examined the factor structure of the original inventory, collected data designed to replicate the factor structure, and I am currently collecting data designed to examine interrelationships between this new inventory and several existing inventories.
My colleagues and I have tested several hypotheses regarding upset over the infidelity of in-laws (Michalski, Shackelford, & Salmon, 2004; Shackelford, Michalski, Schmitt, 2004). Men, more than women, are upset by their partner's sexual infidelity because it put them at risk of investing in unrelated offspring. Women, more than men, are upset by their partner's emotional infidelity because it signaled the diversion of resources away from her and her offspring. Upset over the infidelity of an in-law depends largely on the sex of the related individual. With grandparents, for example, we found support for the hypothesis that older men and women are more upset by their son-in-law's emotional infidelity and more upset by their daughter-in-law's sexual infidelity. Following this same logic, siblings should be more upset over their brother-in-law's emotional infidelity, than by his sexual infidelity, because it signaled the diversion of his resources away from a sister and her offspring. Additionally, siblings should be more upset by their sister-in-law's sexual infidelity, than by her emotional infidelity, because it placed them at risk of investing in unrelated nieces and nephews. This avenue of research has results consistent with those predicted from an evolutionary perspective and it contradicts the belief that men are, in general, more upset by sexual infidelity. This research suggests that men can be more upset by emotional infidelity, than by sexual infidelity, if the perpetrator of the infidelity is mated to a female family member and can also show that women can be more upset over sexual infidelity, than by emotional infidelity, if the perpetrator of the infidelity is mated to a male family member. The results from this study are currently under review (Michalski, Shackelford, & Salmon, 2004). Future research in this area could examine whether these relationships hold for full siblings, half siblings, and stepsiblings.
Evolutionary psychologists have documented a sex difference in the events that trigger jealousy. Men, more than women, are upset by a partner's sexual infidelity. Women, more than men, are upset by a partner's emotional infidelity. Few evolutionary psychologists have sought to understand individual differences in responses to upset over a partner's infidelity and even fewer have looked at changes in jealousy across adulthood. My advisor and I have examined whether sex differences in upset over a partner's sexual and emotional infidelity can be explained by a participant's attachment style (Michalski & Shackelford, 2000; Michalski & Shackelford, 2004). We find support for the hypothesis that sex differences in response to emotional and sexual infidelity as more upsetting will be exaggerated within anxious/ambivalent individuals, relative to the avoidant persons. We found support for this hypothesis in a sample of older adults, and I am currently conducting analyses on a replication of this finding using two measures of attachment in a sample of younger adults. This manuscript, along with others that I have in progress, has the overarching goal of gaining a better understanding of the developmental trajectory of psychological mechanisms in adulthood. In summary, I have several lines of research ongoing that I have successfully completed and have in progress towards the goal of better understanding the psychological underpinnings of families. This research already has resulted in many empirical publications and more than a dozen presentations at local, national, and international conferences with several publications and presentations being co-authored with other graduate students and undergraduate students. In the past four years, I have made substantial contributions to the fields of social/personality psychology, evolutionary psychology and, in particular, to the areas of human parental psychology, sibling psychology, and grandparental psychology.