  How to define and use the concept of inclusive fitness is a contentious topic
in evolutionary theory. Inclusive fitness can be used to calculate selection on
a focal gene, but it is also applied to whole organisms. Individuals are then
predicted to appear designed as if to maximise their inclusive fitness,
provided that certain conditions are met (formally when interactions between
individuals are 'additive'). Here we argue that applying the concept of
inclusive fitness to organisms is justified under far broader conditions than
previously shown, but only if it is appropriately defined. Specifically, we
propose that organisms should maximise the sum of their offspring (including
any accrued due to the behaviour/phenotype of relatives), plus any effects on
their relatives' offspring production, weighted by relatedness. In contrast,
most theoreticians have argued that a focal individual's inclusive fitness
should exclude any offspring accrued due to the behaviour of relatives. Our
approach is based on the notion that long-term evolution follows the genome's
'majority interest' of building coherent bodies that are efficient 'vehicles'
for gene propagation. A gene favoured by selection that reduces the propagation
of unlinked genes at other loci (e.g. meiotic segregation distorters that lower
sperm production) is eventually neutralised by counter-selection throughout the
rest of the genome. Most phenotypes will therefore appear as if designed to
maximise the propagation of any given gene in a focal individual and its
relatives.
