  We demonstrate diversification rather than optimisation for highly
interacting organisms in a well mixed biological system by means of a simple
model and reference to experiment, and find the cause to be the complex network
of interactions formed, allowing species less well adapted to an environment to
flourish by co-interaction over the `best' species. This diversification can be
considered as the construction of many co-evolutionary niches by the network of
interactions between species. Evidence for this comes from work with the
bacteria Escherichia coli, which may coexist with their own mutants under
certain conditions. Diversification only occurs above a certain threshold
interaction strength, below which competitive exclusion occurs.
