"Bacterial conversations: talking, listening and eavesdropping. An introduction"
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Natural selection operates at the level of the individual, with the retention of mutations that benefit that individual. However, current understanding from theoretical ecology suggests that the most important level of organization for a species is the population. That is, communities are more important than the individual, at least in the present day, in maintaining ecological stability. If the processes that drive evolution operate at the level of an individual, but the success is determined at the population level, then evolutionary development can only be effective if individuals are able to interact with other individuals of the same species to ensure the success of the population.One obvious requirement for concerted action by a population is the need for an individual to be aware of and respond to other individuals of the same species that are growing in the vicinity. For many years it was considered that bacteria were simple organisms, with little capacity for the types of interaction seen in higher organisms. The ability to interact was thought to be confined to metabolic consortia, where one bacterium released a compound as a result of its metabolism that was then the substrate for another species. This second species may or may not release a metabolite that could be used by a third species. This simple mechanism results in stable consortia of different species but it is basically an altruistic process where the activity of one organism results in the success of another species."