royalsociety | In a combinatorial communication system, some signals consist of the
combinations of other signals. Such systems are more
efficient than equivalent, non-combinatorial
systems, yet despite this they are rare in nature. Why? Previous
explanations
have focused on the adaptive limits of
combinatorial communication, or on its purported cognitive difficulties,
but neither
of these explains the full distribution of
combinatorial communication in the natural world. Here, we present a
nonlinear
dynamical model of the emergence of combinatorial
communication that, unlike previous models, considers how initially
non-communicative
behaviour evolves to take on a communicative
function. We derive three basic principles about the emergence of
combinatorial
communication. We hence show that the
interdependence of signals and responses places significant constraints
on the historical
pathways by which combinatorial signals might
emerge, to the extent that anything other than the most simple form of
combinatorial
communication is extremely unlikely. We also argue
that these constraints can be bypassed if individuals have the
socio-cognitive
capacity to engage in ostensive communication.
Humans, but probably no other species, have this ability. This may
explain
why language, which is massively combinatorial, is
such an extreme exception to nature's general trend for
non-combinatorial
communication.
