Encyclopedia of Evolutionary Psychological Science

Living Edition
| Editors: Todd K. Shackelford, Viviana A. Weekes-Shackelford

Semen from In-Pair Partner

  • Ray GarzaEmail author
Living reference work entry
DOI: https://doi.org/10.1007/978-3-319-16999-6_738-1



Semen from in-pair partner describes the psychological and adaptive functions of semen during copulation between individuals in a relationship.


Aside from its main role in aiding fertilization, semen production can be influenced by psychological, physical, and social factors that promote its quantity and quality in sexual behaviors. These influences play an adaptive role in increasing the probability that fertilization may occur and aid in reducing the probability of another man fertilizing the ova of their partner. For instance, men have cognitive mechanisms that are sensitive to specific contexts that may doubt their paternity, and this may influence their sexual behavior with their current partner. Additionally, there is evidence to suggest that semen has psychological and biological effects, such as reducing emotional distress (Gallup et al. 2002) and reducing prenatal complications (Koelman et al. 2000). Semen from in-pair partner provides an insight on how human relationships are affected by the perception of infidelity and on the interdependent relationship between copulation and psychological health. Taken together, semen from in-pair partners may suggest the important role of long-term pair bonds where ingestion of semen ejaculate would be most common.

Sperm Competition

Sperm competition is when females engage in sexual intercourse with different men which results in sperm from different partners occupying the reproductive tract (Parker 1970). Although this implies an act of infidelity in a relationship, the thought of unfaithfulness in a relationship can cause changes in semen production and sexual behavior. A man who is at risk of his partner engaging in extra-pair sex may end up investing resources in offspring that are not genetically related (Pham and Shackelford 2015). This may result in psychological and physical changes in a relationship to counter that risk, such as increased semen production, or methods to remove a possible partner’s semen, known as semen displacement. There is a body of research that has looked into time spent away from a current partner and the effects it has on semen quantity in men. Time spent away from a partner puts a man at risk for cuckoldry, as there is no certainty that his partner has been faithful. When away from their partner, men ejaculate more and produce more sperm until their next copulation (Baker and Bellis 1993). This suggests a strategy of sperm competition as an attempt to counter the possibility of another man’s semen in the female’s reproductive tract.

Another tactic that men incorporate when perceiving that their partner have been unfaithful is semen displacement. Semen displacement refers to sexual intercourse where there is deep thrusting to remove semen from a rival male. This can be accomplished by long copulation, where there is more time to remove semen from intercourse, or by quickly ejaculating following an assumption of infidelity. If this strategy is to be effective, then it should be used in situations where there is a likelihood of partner infidelity or where there has been an amount of time of separation where extra-pair copulation may have occurred. In situations where women have male coworkers or male friends that they spend time with, men have reported more semen displacing behaviors, such as increased and deep thrusting (Barbaro et al. 2015). Deep thrusting may be an effective strategy if copulation with another male has been short, where the rival male’s semen is still in the vagina. However, if time between an extra-pair copulation and in-pair copulation has been longer, a shorter copulation with an in-pair partner may be more effective as displacement would not be effective once sperm has entered the reproductive tract and away from the vagina (Barbaro et al. 2015). Semen displacement behaviors are also prevalent in committed relationships (e.g., marriage). It has been reported that men engage in semen displacing behaviors at their next copulation with their partner if their wives spend more time with male friends or male coworkers (Pham et al. 2017). This suggests that sperm competition is not independent of relationship status, but dependent on psychological and environmental factors where one is at risk of cuckoldry.

Perceptions of infidelity may be mediated by mate guarding behaviors. Mate guarding is a costly behavior, but it is effective if it can ascertain faithfulness and paternity certainty. However, this may be determined by the quality of the male that is utilizing mate guarding, such as his level of attractiveness and dominance. It has been found that men who engage in more mate guarding behaviors display lower quality of ejaculate and less quality of sperm than men who engage in less mate guarding behaviors (Leivers et al. 2014). It could be argued that this may be influenced by mate value, where high quality males may not engage in mate guarding behaviors because their high quality traits prevent women from leaving them. Men of low mate value may engage in more mate guarding behaviors because they are at greater risk of their partners leaving them (Leivers et al. 2014).

Psychological Effects of Semen

It has been suggested that semen can have psychological effects when absorbed through the vaginal wall due to the many hormones in the seminal plasma, such as testosterone, prolactin, follicular stimulating hormone, estrogen, and luteinizing hormone (Gallup et al. 2002). Known as Ney’s hypothesis, the effects that seminal plasma has on female behavior is through the modulating effects that prostaglandins have on neurotransmitters. Estrogen can have mood-elevating properties in postmenopausal women and younger women who take estrogen-based contraceptives (Gallup et al. 2002). If semen does have psychological effects, then women who have intercourse without condoms, where semen would be in the reproductive tract, should report less emotional distress, such as depression. Research investigating the role of semen and emotional distress has shown that women who have sex without condoms have fewer depressive symptoms compared to women who use condoms and women who abstain from sexual intercourse. Although it can be argued that this association may be due to sexual frequency, women who have frequent sex with condoms report similar depressive symptoms to women who abstain from sexual intercourse. These effects also carry over to lower suicide attempts in women who do not use condoms when compared to women who use condoms and women who abstain from sexual activity (Gallup et al. 2002).

Preeclampsia Risk and Semen Ingestion

There are many other functions that semen may provide an in-pair partner, whether it is semen obtained through oral or vaginal sex. Although there are many different reasons why couples engage in oral sex (i.e., arousal, pleasure, rival detection), the benefits of fellatio on women has not been fully explored. There seems to be an important role that semen plays in couples who are expecting children, which may highlight a function of oral sex where it is dependent that the female swallows the semen. In women who are pregnant, preeclampsia is a complication that results in hypertension and can lead to severe consequences in pregnancy. Research has shown semen may be beneficial in women who are at risk for preeclampsia (Koelman et al. 2000). Prior to gestation, semen has been found to induce immunological responses in women who ingest their partner’s semen through oral sex resulting in a reduce likelihood of preeclampsia. This is through the result of molecules in semen that aid in inducing immunological tolerance in women.

Are the benefits of semen ingestion dependent on relationship context? Research has investigated if these effects can be explained by women who receive semen through their own partner (in-pair) or semen received through an out-pair, such as donor sperm. There are many reasons why women would want to receive donor sperm, such as issues related to infertility, or lesbian couples who are trying to conceive. In looking at the risk of preeclampsia, it has been shown that women who receive semen from a donor are at a significant increase from developing preeclampsia compared to receiving semen from their partner (Gonzalez-Comadran et al. 2014). Although the findings are unclear as to why donor semen would increase preeclampsia, it points to the important role that relationship context may have on semen ingestion in developing preeclampsia.


Semen serves as an important vehicle for transporting sperm in an attempt to fertilize an ova. This process can be modulated by environmental and psychological factors where a male may feel compromised as to his certainty in paternity. This discrepancy may influence the amount of semen produced, as well as the behaviors utilized to combat the possibility of a rival’s sperm inside the reproductive tract of a partner, as is seen in semen displacement. Although sperm competition has received a lot of attention in the literature, semen’s influential role to mental health and prenatal care is equally important. It is noteworthy to point that these influences may be the result of relationship context, where semen ingestion may be dependent upon semen obtained from a committed relationship (in-pair partner).


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© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.Oklahoma State UniversityStillwaterUSA

Section editors and affiliations

  • Jennifer Byrd-Craven
    • 1
  1. 1.Oklahoma State UniversityStillwaterUSA