Personality Traits Increasingly Important for Male Fertility: Evidence from Norway

Revolutionizing Infertility Management through Novel Peptide-based Targets

Around 48 million couples and 186 million people worldwide have infertility; of these, approximately 85% have an identifiable cause, the most common being ovulatory dysfunctions, male infertility, polycystic ovary syndrome, and tubule disease. The remaining 15% have infertility for unknown reasons, including lifestyle and environmental factors. The regulation of the hypothalamic- pituitary-adrenal axis (HPA) is crucial for the secretion of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH), which are essential for female reproductive functions. GnRH is the primary reproductive axis regulator. The pattern of GnRH, FSH, and LH release is determined by its pulsatile secretion, which in turn controls endocrine function and gamete maturation in the gonads. Peptides called Kisspeptin (KP), Neurokinin-B (NKB), and Orexin influence both positive and negative feedback modulation of GnRH, FSH, and LH secretion in reproduction. This review article mainly focuses on the historical perspective, isoform, and signaling pathways of KP, NKB, and Orexin novel peptide-based targets including clinical and preclinical studies and having a promising effect in the management of infertility.

The prospective power of personality for childbearing: a longitudinal study based on data from Germany

The link between personality and fertility is relatively underexplored. Moreover, there are only a few studies focusing on the prospective association between personality and childbearing. However, none of these studies considered the Five-Factor Model (FFM), which is the most widely accepted measurement of personality. The present study fills this gap by examining the prospective association between the FFM and the hazard ratio of the first and the second childbirth in Germany. Analyses are based on recent data (2005–2017) from the Socio-economic Panel Study. Cox proportional hazard models are applied. Findings demonstrate that personality traits are associated with fertility. Extraversion is positively linked with the first childbirth, but is negatively associated with the second childbirth. These findings are mainly driven by males. Agreeableness is positively linked with the first childbirth across the total sample. Again, this correlation is mainly based on the findings for men, among whom a positive association between agreeableness and the second childbirth is also found. Among women, personality does not seem to be linked with the first childbirth. However, the risk of having a second child is found to be negatively associated with conscientiousness. My study adds to the current understanding of the personality–fertility association by exploring the impact of personality trait scores from the FFM on subsequent fertility behavior. However, further research is needed on the association between personality and childbearing; on the mechanisms through which personality affects fertility; and on how these links differ across cultures, among higher parities, and for births after re-partnering.

Is the Predisposition to Have More Children Beneficial among Parents with Only One Child? Evidence from Spanish Parents

The fertility deficit in many European countries is related to a low rate of second births. Understanding the factors associated with the predisposition of one-child parents to have more children could contribute to the search for solutions to this social problem. Although previous evidence highlights the role of employment and social factors, psychological factors have been poorly investigated. This study examines the relationship between different psychosocial factors (rumination, personality, life satisfaction, perfectionism, social support, parental stress, guilt linked to work–family conflict, age and child temperament) and parents’ predisposition to have more children. The sample consisted of 96 one-child Spanish parents whose child was in early childhood education (59.3% women; M_age = 37.41). The results show that one-child parents with the predisposition to have more children, compared to those without a predisposition to have more children, showed higher levels of life satisfaction, extroversion and adaptive perfectionism but lower levels of rumination and parental stress. The social implications of these findings and how they may affect parenting today are discussed.

Childhood hearing impairment and fertility in Norway

There is a lack of studies assessing how hearing impairment relates to reproductive outcomes. We examined whether childhood hearing impairment (HI) affects reproductive patterns based on longitudinal Norwegian population level data for birth cohorts 1940-1980. We used Poisson regression to estimate the association between the number of children ever born and HI. The association with childlessness is estimated by a logit model. As a robustness check, we also estimated family fixed effects Poisson and logit models. Hearing was assessed at ages 7, 10 and 13, and reproduction was observed at adult ages until 2014. Air conduction hearing threshold levels were obtained by pure-tone audiometry at eight frequencies from 0.25 to 8 kHz. Fertility data were collected from Norwegian administrative registers. The combined dataset size was N = 50,022. Our analyses reveal that HI in childhood is associated with lower fertility in adulthood, especially for men. The proportion of childless individuals among those with childhood HI was almost twice as large as that of individuals with normal childhood hearing (20.8% vs. 10.7%). The negative association is robust to the inclusion of family fixed effects in the model that allow to control for the unobserved heterogeneity that are shared between siblings, including factors related to the upbringing and parent characteristics. Less family support in later life could add to the health challenges faced by those with HI. More attention should be given to how fertility relates to HI.

How Does Birth Order and Number of Siblings Affect Fertility? A Within-Family Comparison Using Swedish Register Data

This study examines how the sibling constellation in childhood is associated with later fertility behaviour of men and women in Sweden. Administrative register data are used to investigate how birth order affects completed fertility, how the number of siblings and birth order jointly affect completed fertility, and in both cases if there are gender differences in these relationships. Our data consist of all fully biologically related siblings in Sweden whose mothers were born between 1915 and 1935 (the younger generation is born primarily in the 1940s, 1950s and 1960s; N = 1,472,813). To study the direct effect of birth order on fertility, sibling comparison models are applied, while to analyse the joint effect of number of siblings and birth order, the sample was stratified by birth order. Results show that higher birth order has a negative effect on completed fertility for women; hence, earlier-born women show overall higher fertility than later-born women. Parity transitions indicate that later-born women are less likely to have two or more children, while no overall gradient for men can be found. The number of siblings is more positively associated with completed fertility for firstborn than for later-born individuals. We conclude that the position in the family of origin can be seen as an additional factor that influences fertility, although effect sizes are rather small.

Mental health problems in adolescence, first births, and union formation: Evidence from the Young HUNT Study

While a large literature documents how mental health problems in adolescence have long-term consequences for adult socioeconomic outcomes, less is known about the relation with family-formation behavior. In this paper, we use data from a population based Norwegian health survey (the Young-HUNT study) linked to administrative registry data (N = 8,113) to examine the long-term consequences of symptoms of internalizing and externalizing problems, the two most common forms of mental health problems, on family-formation outcomes: the likelihood of a first birth, the union status of a first birth, and entering first marriage. For men, externalizing problems are associated with earlier parenthood, especially becoming a father without having a coresidential relationship with the child's mother. Internalizing problems, on the other hand, are associated with lower first-birth rates and the association grows progressively stronger with age. We also find that the associations are more pronounced among men with low childhood socioeconomic status. In contrast, women's family-formation appears for the most part unrelated to their mental health.

An Evolutionary Ecological Framework for Understanding Human Behavioral Syndromes: Commentary on Lukaszewski et al. 2017

In their recent paper, Lukaszewski et al. proposed a socioecological hypothesis for analyzing the covariations between the Big Five personality traits. The hypothesis states that the shared variance between the personality traits is higher in less complex societies marked by lower economic development, urbanization, and niche diversity. We welcome this hypothesis and add an additional framework for understanding the covariation between the traits—behavioral syndromes. We state that behavioral syndromes and their effects on fitness should be the primary target for the evolutionary ecological analysis of the relations between human personality traits on a population level. Behavioral syndromes are extensively studied in animal behavioral ecology which provides an opportunity for the comparative study of personality. We point to the behavioral syndromes in Lukaszewski et al. data, especially to the agreeableness–conscientiousness correlation, which roughly corresponds to the aggressiveness–impulsiveness behavioral syndrome in animals. We point to other potentially problematic issues and provide recommendations for future research.

The Role of Personality in Sexual and Reproductive Health

Strong evidence suggests that sexual behavior and reproductive success can be predicted by personality traits. Here, I review new studies that have contributed to the understanding of these associations and outline potential avenues for further research. Findings show that extraversion is the most important personality trait in sexual behavior (number of lifetime sexual partners, involvement in casual sex, marital infidelity, condom use, male and female sexual dysfunction, sexual coercion, and sexual harassment) and that neuroticism, agreeableness, and conscientiousness are also associated with these outcomes. Extraversion has emerged as the most important personality trait for fertility in men but appears relatively unimportant for fertility in women. Findings for other personality traits are somewhat mixed, probably because of variations in research design, and further prospective studies are recommended to address potential bidirectional associations. Further research is also needed in adolescent samples, in understudied topic areas (e.g., sexually transmitted infections, biomarkers of fertility), and on personality similarity between sexual partners in samples from both poor and developed nations.

Assessing the Structure of the Five Factor Model of Personality (IPIP-NEO-120) in the Public Domain

Assessment of individual differences in personality traits is arguably one of the hallmarks of psychological research. Testing the structural validity of trait measurements is paramount in this endeavor. In the current study, we investigated 30 facet traits in one of the accessible and comprehensive public-domain Five Factor Model (FFM) personality inventories, IPIP-NEO-120 (Johnson, 2014), using one of the largest US samples to date (N = 320,128). We present structural loadings for all trait facets organized into respective FFM-trait domain (Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness). Both hierarchical second-order and bi-factor models showed tolerable model fit indices, using confirmatory factor analysis in a structural equation modeling (SEM) framework. Some facet traits were substantially more representative than others for their respective trait domain, which facilitate further discussions on FFM-construct content. We conclude that IPIP-NEO is sufficiently structurally robust for future use, for the benefit of research and practice in personality assessment.

Trends in Childlessness Among Highly Educated Men in Sweden

Among men with post-secondary degrees in Sweden, one in four are childless by age 45, and this level has been constant over time (in this study, for men born 1956–1972). This high level of childlessness is somewhat surprising in the context of a significant gender imbalance among the highly educated (and thus the relative scarcity of highly educated men). In this study, I examine differences in childlessness among the highly educated by studying how educational prestige, social class, and income are associated with the likelihood of becoming a father. Higher income and social class background are positively associated with fatherhood, and this association has not changed over time. Educational prestige (higher degrees, or degrees from traditional universities) is not positively associated with fatherhood, while 2-year degrees have become more positively associated with fatherhood over time. The findings of this study suggest that socioeconomic resources are important for men's family formation in Sweden compared to educational resources, contrary to expectations from educational homophily and partner market perspectives.

A 10-year prospective study of personality and reproductive success: Testing the mediating role of healthy living

OBJECTIVE

There is some evidence that personality relates to childbearing in adulthood but the importance of personality for reproductive capacity is unknown. This study explored cross-time associations between the major dimensions of trait personality and self-reported fertility and fecundity.

METHODS

A representative sample of young Australian adults [n = 4501; age range ≈ 18-44 (women), 18-54 (men)] provided information on personality, fertility, fertility intentions, fecundity and lifestyle factors (cigarette smoking, alcohol consumption, physical activity) in 2006 and again in 2016. Older Australian adults [n = 4359; age ≥ 45 (women), ≥ 55 (men)] provided information on personality, lifestyle factors and completed fertility.

RESULTS

After controlling for sociodemographic factors, completed fertility was associated with higher agreeableness in both sexes, and lower conscientiousness and openness in women. In younger adults, higher levels of openness were associated with fewer children 10 years later in both sexes, and higher extraversion was associated with more children 10 years later in men. The association between fertility intentions and subsequent fertility was stronger among women scoring higher on conscientiousness, and women scoring higher on neuroticism were more likely to acquire medical or health difficulties in having children - an effect that was mediated by higher levels of cigarette smoking.

CONCLUSIONS

The study provides initial evidence for an association between personality and the acquisition of difficulties in having children.

Women's spousal choices and a man's handshake: Evidence from a Norwegian study of cohort differences

Both high grip strength and being married independently relate to better functional capacity and health at older ages, but the combined effect of marital status and strength have not been investigated. Especially at older ages, declining strength can have adverse health and social consequences, where having a spouse could potentially help with everyday support and alleviate some of the negative effects of sarcopenia. We investigate how grip strength relates to being married among two cohorts of 59–71 year olds (born 1923-35 and 1936-48) in the Norwegian city of Tromsø, controlling for a broad set of health variables and sociodemographic characteristics. The baseline included N = 5009 participants of whom 649 died during follow-up. We find that for men, particularly among younger cohorts, the physically stronger are more likely to be married, but no relation is found for women. This is consistent with a hypothesis that women increasingly have selected male marital partners based on preferred individual traits, whereas men do not emphasize strength when selecting women. We find that both marital status and grip strength independently affect mortality, but there is no significant joint effect. However, the distribution of strength and marital status implies that more men than women and increasing shares of later born cohorts have a “double-burden” of low strength and a lack of support from a spouse.

Fertility history and use of antidepressant medication in late mid-life: a register-based analysis of Norwegian women and men

OBJECTIVES

Life course influences on later life depression may include parenting trajectories. We investigate associations between number and timing of births and use of antidepressant medication in late mid-life using data on the whole Norwegian population.

METHODS

We estimated logistic regression models to analyse variations in the purchase of antidepressants between 2004 and 2008 by timing of births and number of children among women and men aged 45-73, using Norwegian population register data. We controlled for age, education, marital and partnership status, and (in some models) family background shared among siblings.

RESULTS

Mothers and fathers of two or more children were generally less likely to purchase antidepressants than the childless. Mothers who started childbearing before age 22 were an exception, although according to sibling models they were not more likely to purchase antidepressants. All models showed that women who became mothers before age 26 and had only one child had higher odds of medication purchase than the childless. Older age at first birth was generally associated with lower risks of antidepressant purchase.

CONCLUSION

This analysis of high-quality data for a national population indicates that early motherhood, childlessness and low parity are associated with higher usage of antidepressants in late mid-life. Our data did not allow identification of mediating pathways, and we lacked information on early mental and physical health and some other potentially important confounders not shared between siblings. Furthermore purchase of antidepressants is not a perfect indicator of depression. Those concerns aside, the results suggest complex effects of fertility on depression that merit further investigation.

The evolved psychological mechanisms of fertility motivation: hunting for causation in a sea of correlation

Cultural, ecological, familial and physiological factors consistently influence fertility behaviours, however, the proximate psychological mechanisms underlying fertility decisions in humans are poorly understood. Understanding the psychological mechanisms underlying human fertility may illuminate the final processes by which some of these known predictors have their influence. To date, research into the psychological mechanisms underlying fertility has been fragmented. Aspects of reproductive psychology have been examined by researchers in a range of fields, but the findings have not been systematically integrated in one review. We provide such a review, examining current theories and research on psychological mechanisms of fertility. We examine the methods and populations used in the research, as well as the disciplines and theoretical perspectives from which the work has come. Much of the work that has been done to date is methodologically limited to examining correlations between ecological, social and economic factors and fertility. We propose, and support with examples, the use of experimental methods to differentiate causal factors from correlates. We also discuss weaknesses in the experimental research, including limited work with non-WEIRD (western, educated, industrialized, rich and democratic) populations.

What Explains the Heritability of Completed Fertility? Evidence from Two Large Twin Studies

In modern societies, individual differences in completed fertility are linked with genotypic differences between individuals. Explaining the heritability of completed fertility has been inconclusive, with alternative explanations centering on family formation timing, pursuit of education, or other psychological traits. We use the twin subsample from the Midlife Development in the United States study and the TwinsUK study to examine these issues. In total, 2606 adult twin pairs reported on their completed fertility, age at first birth and marriage, level of education, Big Five personality traits, and cognitive ability. Quantitative genetic Cholesky models were used to partition the variance in completed fertility into genetic and environmental variance that is shared with other phenotypes and residual variance. Genetic influences on completed fertility are strongly related to family formation timing and less strongly, but significantly, with psychological traits. Multivariate models indicate that family formation, demographic, and psychological phenotypes leave no residual genetic variance in completed fertility in either dataset. Results are largely consistent across U.S. and U.K. sociocultural contexts.

Work-Family Conflict Moderates the Relationship Between Childbearing and Subjective Well-Being

Many empirical studies find that parents are not as happy as non-parents or that parenthood exerts a negative effect on subjective well-being (SWB). We add to these findings by arguing that there is a key moderating factor that has been overlooked in previous research, i.e. the level of work-family conflict. We hypothesize that the birth of a child means an increase in the level of work-family tension, which may be substantial for some parents and relatively weak for others. To outline such an approach, we estimate fixed-effects models using panel data from the Household, Income and Labor Dynamics in Australia survey. We find that childbearing negatively affects SWB only when parents, mothers in particular, face a substantial work-family conflict, providing thus support for our hypothesis.

Genotype × cohort interaction on completed fertility and age at first birth

Microevolutionary projections use empirical estimates of genetic covariation between physical or psychological phenotypes and reproductive success to forecast changes in the population distributions of those phenotypes over time. The validity of these projections depends on relatively consistent heritabilities of fertility-relevant outcomes and consistent genetic covariation between fertility and other physical or psychological phenotypes across generations. However, well-documented, rapidly changing mean trends in the level and timing of fertility may have been accompanied by differences in the genetic mechanisms of fertility. Using a sample of 933 adult twin pairs from the Midlife Development in the United States study, we demonstrate that genetic influences on completed fertility and age at first birth were trivial for the 1920-1935 birth cohort, but rose substantially for the 1936-1955 birth cohort. For the 1956-1970 birth cohort, genetic influences on completed fertility, but not age at first birth, persisted. Because the heritability of fertility is subject to change dynamically with the social context, it is difficult to project selection pressures or the rate at which selection will occur.