Three Hypotheses on the Evolution of Romantic Relationships

This entry was written by Lachlan Barrett as part of a project done in BIAN 2133 ‘Human Reproductive Strategies’ at The Australian National University in 2019 Semester 2.


Romantic relationships are a complex phenomenon, as they are experienced through different socioemotional frameworks that occur in diverse contexts (Hazan & Shaver, 1987). Following the work of John Bowlby’s attachment theory beginning in 1969, which described caregiver-offspring bonds as an attachment-behavioural system where affectional bonds can develop (Bowlby, 1969). The theory has since evolved to be of interest to a diverse range of scientific disciplines, one of which being the evolutionary sciences. It was in 1987, however, that Cindy Hazan and Philip Shaver began to apply attachment theory to adult attachment or romantic love. Hazan and Shaver explored how romantic love was a biosocial process, where attachment to one’s adult lover could is compared to the affectional bond between an infant and its parents (Hazan & Shaver, 1987).

In this entry, I will present three evolutionary hypotheses as to why romantic relationships could have evolved: The Paternal-Care Hypothesis (PCH), the Concealed-Ovulation Hypothesis (COH), and the Neoteny Hypothesis (NH).

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The Paternal-Care Hypothesis

The PCH postulates that romantic relationships could have evolved due to the increasing role of paternal care in humans. The evolutionary logic behind this idea is grounded in the conflict of interests males face when investing time and resources to ensure the survival of their offspring (i.e. parenting effort) versus the effort they can place into acquiring new mates (i.e. mating effort)(Gray & Crittenden, 2014). According to this hypothesis, a strong bond (i.e. romantic love) between committed mates increases the inclusive fitness of subsequent offspring, by the male providing extra resources and protection (Fraley & Shaver, 2000). Interestingly, Chimpanzees and Bonobos, our closest genetic relatives, do not exhibit attachment through committed romance relationships or have an increased paternal care investment strategy (Jaeggi, Boose, White, & Gurven, 2016).

Despite, females carrying the majority of the reproductive costs such as gestation and lactation, males can mitigate these costs by investing resources, increase protection efforts, and sharing caregiver responsibilities (Gray & Crittenden, 2014). There are many evolutionary benefits for males to investment in this stratagem. One of which is increased paternal certainty, having an exclusive, monogamous relationship (i.e. a romantic relationship) allows the male to have increased confidence that any sequence offspring of that relationship are his. Another benefit resides in increased offspring survivorship, this further increases inclusive fitness by direct resource and care investments and protecting offspring from unrelated males. Therefore, romantic relationships provide a medium for males to increase their mating and parenting efforts in tandem. Thereby investing in one female and their subsequent offspring as opposed to a greater number of superficial relationships.

The Concealed-Ovulation Hypothesis

Unlike many primate species, such as baboons, humans have evolved mechanisms to conceal their ovulation status and mimic sexual receptiveness, this is seen in the increased size of the hips, breasts and buttocks (Rooker & Gavrilets, 2018). Due to this uncertainty when determining whether a female is ovulating or not has meant that males have had to adapt to their mating strategies (i.e. forming a romantic relationship). Whereby engaging in constant mate guarding ensures that reproductive privileges could be maintained throughout the female’s menstrual cycle (Gray & Crittenden, 2014).

From a theoretical perspective, this shift in pair-bonding may equate to a sum benefit for both females and males. For females, concealed ovulation meant they could benefit from the increased support males would invest in them (Rooker & Gavrilets, 2018). For males, they would benefit by ensuring paternal certainty and protecting their offspring from non-related males, ensuring their maturation (Gray & Crittenden, 2014). Both sexes would also benefit from the emotional support and companionship that would be acquired by forming a romantic relationship (Hazan & Shaver, 1987).

However, females may benefit exclusively by using concealed ovulation as a means to engage in sexual acts through their cycle to invest more in short-term resource acquisition. This strategy has been seen in Bonobos, where they use sexual contacts to acquire relatively limited resources without having to invest in long-term bonds (Jaeggi et al., 2016). Despite this potential for cheating, romantic relationships have evolved as a system where trust, commitment, and companionship, are at the forefront of this behavioural attachment arrangement.

The Neoteny Hypothesis

Another proposed possibility for the evolution of romantic relationships is as a by-product of humanity’s retention of juvenile traits in adulthood (neoteny) (Fraley & Shaver, 2000). This hypothesis proposes that changes to our developmental procedure and timing have had profound effects on our evolution; such as our inclination for forming romantic relationships. This evolutionary adaptation began due to the increasing size of our braincases and cognitive capacity; as a consequence, it was becoming problematic for infants to fit through the birth canal. This circumstance led to humans being born cognitively underdeveloped in contrast to other primates (Jaeggi et al., 2016). Due to this delayed ontogeny, parent-offspring bonds were paramount, as they were solely dependent on their caregivers to survive. Therefore, the development of romantic relationships is just another instance of retained neoteny.

In other primates, parent-offspring attachment bonds exist, but as the infant develops and matures, this capacity for attachment is ‘turned off’ (Fraley & Shaver, 2000). However, in humans, this development hurdle does not exist, and we continue to be sensitive to attachment-behavioural systems such as romantic relationships. This concept is how Hazan and Shaver (1987) initially associated offspring-parent bonds to adult attachment relationships, suggesting that the latter evolved from the former, as commonalities exist between the two.


Romantic relationships are a multifaceted biosocial process that can be explained in many ways. This article has presented three hypotheses as to why romantic relationships could have evolved. The PCH described that an increase in paternal parental investment led to the evolution of romantic relationships. The COH postulates that romantic relationships evolved because of the concealment of female ovulation cues and sexual mimicry, resulting in males having to invest in long-term mating strategies to secure sexual opportunities. Finally, the NH believes that romantic relationships evolved as a delayed ontological process similar in scope to how infants attach to their primary caregivers.

Literature Cited

Bowlby, J. (1969). Attachment and loss: volume I: attachment. In Attachment and Loss: Volume I: Attachment (pp. 1-401): London: The Hogarth Press and the Institute of Psycho-Analysis.

Fraley, R. C., & Shaver, P. R. (2000). Adult romantic attachment: Theoretical developments, emerging controversies, and unanswered questions. Review of general psychology, 4(2), 132-154.

Gray, P. B., & Crittenden, A. N. (2014). Father Darwin: Effects of Children on Men, Viewed from an Evolutionary Perspective. Fathering, 12(2), 121. doi:10.3149/fth.1202.121

Hazan, C., & Shaver, P. (1987). Romantic Love Conceptualized as an Attachment Process. Journal of personality and social psychology, 52(3), 511-524. doi:10.1037/0022-3514.52.3.511

Jaeggi, A. V., Boose, K. J., White, F. J., & Gurven, M. (2016). Obstacles and catalysts of cooperation in humans, bonobos, and chimpanzees: behavioural reaction norms can help explain variation in sex roles, inequality, war and peace. Behaviour, 153(9-11), 1015-1051. doi:10.1163/1568539X-00003347

Rooker, K., & Gavrilets, S. (2018). On the evolution of visual female sexual signalling. Proceedings. Biological sciences, 285(1879), 20172875. doi:10.1098/rspb.2017.2875

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