Take the properties of the elements hydrogen and oxygen. These are thoroughly understood in themselves. Yet nobody has ever succeeded in predicting the properties of water from a knowledge of its constituent elements. Trying to explain why water spirals down a plughole simply from a knowledge of atoms is an impossible task. What's missing is a knowledge of fluids-a whole level of order above that of individual atoms.
Physicists see water for what it is - a fluid.
There is nothing unscientific about this approach. It simply acknowledges that certain phenomena cannot be predicted. Turning back to biology and social insects, we can ask what is the appropriate level to explain the cooperative behaviour of a colony as a whole. Probably the most popular approach to biological phenomena these days is to try to explain them in terms of the properties of genes. According to evolutionary thinking, if a genetic mutation changes an individual's structure or behaviour in a way that gives it a competitive edge over others, then it will be favoured by natural selection and passed on to future generations.