The majority of historically known human societies
have allowed, and still allow, polygynous mating.
Yet, in some of the most successful agricultural
societies, polygyny was gradually replaced by
socially imposed monogamy, beginning with the
transition from hunter–gatherers to agriculturalists
and the resulting larger residential groups.
Subsequently, a disproportionate amount of the
world’s population growth in recent millennia has
been driven by a relatively small number of
societies, many of which practice socially imposed
Some societies, such as the ancient Romans, imposed
monogamous marriage but permitted extramarital
sexual relations in brothels, so long as moderation
was exercised. On the other hand, some partible
paternal societies in South America encourage
extramarital polyandrous mating. Hence, although
marriage and mating are closely related, there is
not always one-to-one correspondence.
These examples illustrate the enormous variability
in sexual norms, which should be expected if norms
are complex phenomena determined by multiple
mechanisms. It is therefore improbable that any
single hypothesis could explain the entire range of
Socially imposed monogamy in humans is an
evolutionary puzzle because it requires costly
punishment by those who impose the norm.
Moreover, most societies were — and are — polygynous;
yet many larger human societies transitioned from
polygyny to socially imposed monogamy beginning with
the advent of agriculture and larger residential
Researchers used a simulation model to explore how
interactions between group size, sexually
transmitted infection (STI) dynamics and social
norms can explain the timing and emergence of
socially imposed monogamy.
Polygyny dominates when groups are too small to
However, in larger groups, STIs become endemic
(especially in concurrent polygynist networks) and
have an impact on fertility, thereby mediating
Punishment of polygynists improves monogamist
fitness within groups by reducing their STI
exposure, and between groups by enabling punishing
monogamist groups to outcompete polygynists.
This suggests pathways for the emergence of socially
imposed monogamy, and enriches our understanding of
costly punishment evolution.
For more information
Chris T. Bauch & Richard McElreath
Disease dynamics and costly punishment can foster
socially imposed monogamy