Sunday, December 12, 2010

How do I know if my partner is cheating on me - evolution, sexuality and relationships

Last week I gave a talk on Personality and Sexuality. One question that cropped up was - "How do I know if my partner is cheating on me?" By chance the next morning there was a newspaper article attributing uncommitted sex, one-night stands, and acts of infidelity to genetics.

Individuals who have frequent sex with multiple partners are psychologically different from those who have frequent sex with single partner (Simpson & Gangestad, 1991). This sociosexual difference places individuals in two groups
  1. Unrestricted sociosexual types, have a higher number of sexual partners, and one night stands. They have a permissive attitude to casual and uncommitted sex.
  2. Restricted sociosexual types, require greater closeness and commitment before sex with their romantic partner.
 Genetics plays an important role in sociosexuality
Genes evolve to enhance survival of the species. From an evolutionary viewpoint females reproduce with a mate who will invest in their offspring and produce offspring with an advantaged genetic makeup. Female socio-sexual orientation exists because males vary in the quality of their genes.
  • Unrestricted type females benefit from passing the genes of men with greater reproductive success to their own offspring. To induce males to invest in their offspring they frequently engage in pretense and deceit, traits that are strongly associated with unrestricted sociosexuality.
  • Restricted type females benefit from caring males who limit reproductive efforts to the females own offspring.
  • Male sociosexuality evolved through competition. Males who do not succeed with an unrestricted socio-sexual orientation become Restricted.

How do you know your partner's sociosexuality?
Lynda Boothroyd showed that observers were able to identify restricted vs. unrestricted individuals from cues in thier faces. My audience successfully differentiated the Restricted and Unrestricted pairs from the same picture. Test yourself.

What does this mean for a relationship?
  • Restricted socio-sexual personalities are more willing to remain in an unsatisfactory marriage. They are less likely to be drawn out of such a relationship by attractive alternate partners.
  • For Unrestricted individuals long term stability in the relationship depends on the extent to which the partner is highly attractive and possesses high social visibility. Decisions to continue or terminate a relationship depend more on changes in the partners physical attractiveness and social status.

However, personality is not all in the genes. Genes contribute to the biological aspect of personality - temperament. Personality also has an acquired aspect - character. When fully developed, character defines the mature personality.

How do I know if my partner is cheating on me?
To return to the question. Asking the question indicates there are already boundaries being overstepped. It indicates an erosion of trust - a core component in any long-term relationship. That is what needs to be addressed.

Jeffry A Simpson, Steven W Gangestad. Personality and sexuality: empirical relations and an integrative theoretical model. In: Sexuality in close relationships. Kathleen McKinney, Susan Sprecher Editors. Lawrence Erlbaum Associates. New Jersey. 1991:71-92.


  1. Hi!
    Yes it is trust! But where do you draw lines? Its not only "being identified as Restricted or Unrestricted" through socio status,visibility/ physical attraction or strong genetic factors.
    What about failures in boyfriends and girlfriends who divorce their feelings on petty issues or trivial matters? or non sexual issues? Again its trust which breaks us apart.
    I think our priorities between time and situations change and helps us to "trust "and "mistrust" repeatedly to one person or different persons leaving it with excuses!Understanding? If one may call it!
    Having sex with another person known or unknown or falling in love at first sight or just coping with situations or having hormonal triggers biologically where one partner male/ female feels interested or cheats on himself or herself.-(either married or live-in relationships or being friends) I feel its biological & impulsive reaction of self with physical and bio chemical parameters present in the body and undernourished sexual needs which makes anybody play or be calm. The environment around him and his wired circuit of his sexuality without knowledge awareness and control , balance of mind and body and limited understanding controls our behavior.But scientifically or philosophically what is right or wrong? Anything right for one will be wrong for the other.So it is to be addressed individually and respected. Finders keep it losers loose it! find paths to keep it! There is no cheating!!!!! Nothing is permanent or owned in this world so is love when you look at it abstractly.
    hope I have not said anything wrong!!!!!!!

  2. Srini, trust and boundaries, both matter. An individual needs to come to terms with what he or she is comfortable with and address issues that are disturbing.

    Your right!!!! 'Right' or 'wrong' is more difficult when looked at philosophically. From a science or mental health point of view it may be easier to view it in terms of outcomes - which behaviours are associated with the best outcomes for the individual and the relationship. There is usually a general indication of the likely outcome of a particular behaviour, but individual reactions may not be so predictable.

  3. Dear Neville
    I think honesty and commitment are important in any relationship. If one person is him or herself is honest in relationship it is unlikely that he or she will suspect his or her partner of infidelity. Thuogh there may be many temptations one has to resist these and learn to be faithful to the partner

  4. Dalbara, thanks and welcome. Individuals differ in the degree of intimacy they are comfortable with outside of the relationship. They tend to set psychological boundaries of acceptable outside intimacy. When these boundaries are crossed the issue of infidelity comes up. Yes, it will require commitment to address this - either to increase the trust or to curtail the boundaries. Asking the title question indicates problems in this area. Whether or not grounded in reality, these problems need to be addressed.