The complexity of brain organisation is greater for
animals that must contend with a varied environment.
Such animals have an elaborate motivational system
that allows them to think about the impacts of that
environment and then take appropriate decisions.
Some kinds of feeding methods and predator avoid-
ance demand a great cognitive capacity, but the most
demanding thing in life for humans and many other
species is to live and organise behaviour effectively in
a social group (Humphrey 1976, 1992, Broom 1981,
2003). Animals that live socially are generally more
complex in their functioning and in their cognitive
capacity than related animals that are not social. When
deciding whether animals are sentient, a first step is
the analysis of the degree of complexity of living that is
possible for the members of the species (D. M. Broom &
K. E. Littin unpubl.). Without a level of brain function-
ing that makes some degree of awareness possible
(Sommerville & Broom 1998), an animal could not nor-
mally be sentient.