Eusociality is an advanced form of social organization, where some individuals reduce their reproductive potential to raise the offspring of others. Eusociality is rare but hugely successful: only about 2% of insects are eusocial but they represent 50% of the insect biomass. The biomass of ants alone exceeds that of all terrestrial non-human vertebrates combined. I will present a simple model for the origin of eusociality. In the solitary life style all offspring leave to reproduce. In the primitively eusocial life style some offspring stay and help raise further offspring. A standard natural selection equation determines which of those two reproductive strategies wins for a given ecology. The model makes simple and testable predictions without any need to evoke inclusive fitness theory. More generally, I will discuss the limitations of inclusive fitness theory. I will argue: once fitness is calculated in a standard model of natural selection every aspect of relatedness is included. Further reading: Nowak MA, CE Tarnita, EO Wilson (2010). The evolution of eusociality. Nature 466: 1057-1062. (see also: http://www.ped.fas.harvard.edu/IF_Statement.pdf) Nowak MA, Highfield R (2011). SuperCooperators: Why We Need Each Other to Succeed. Free Press.