Abstract

Reproductive success (fitness) is the currency for species evolution, and therefore, the
establishment of sexual relationships is one of the most fundamental interactions underlying
life on Earth. Sexual selection theory aims to explain the strength and implications of sexual
bonds as a result of traits that evolve to influence sexual encounters and thus, reproductive
success. Humans offer a valuable ‘model’ to understand the nature of sexual behaviour,
especially because their preferences can be directly communicated by individual participants,
in contrast with non-human animals in which preferences are inferred from behavioural
observations. The high social complexity of humans has led to multiple approaches to
understand individuals’ attitudes and behaviours within an eco-evolutionary context,
particularly with regards to investigating how ‘attractiveness’ traits influence sexual
relationships, and how the expression of these traits matches sexual outcomes (i.e., as a proxy
for mating success). Although humans traditionally fall between a polygyny and serial
monogamy mating system, it remains poorly known how promiscuity is associated with a
ubiquitous factor underlying human social/sexual dynamics: ‘love’. This research investigated
how promiscuity (measured as numbers of self-reported sexual partners and as the desire to
be promiscuous) and simultaneous love (individuals declaring whether they can ‘fall in love’
with more than one person simultaneously) are affected by a number of different traits (gender,
age, self-assessed attractiveness, sexual orientation) and interpreted under predictions of
sexual selection theory. Using a newly generated dataset, it was quantified how self-assessed
attractiveness traits influence the expression of promiscuous desires across participants. The
majority (84.5%) of participants displayed a desire for promiscuity. Gender and sexual
orientation are the main variables in which there is a relationship in participant’s desires for
promiscuity and simultaneous love. Notably, this research revealed that more than half of the
individuals in the sample (57.1%) expressed the possibility to love more than one person
simultaneously. This finding goes against fundamental norms underlying monogamous sexual
relationships in most human societies. Collectively, this thesis provides novel data to further
discuss promiscuity in humans.