http://www.biomedcentral.com/1471-2180/9/191/abstract

Streptococcus pneumoniae populations have the telltale signs of high recombination with competence implicated as the major driving force behind gene exchange. Competence in S. pneumoniae is triggered by a quorum-sensing mechanism controlled by the competence-stimulating peptide pheromone.
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Evidence of pheromonal communication exists in bacteria that do not sexually reproduce. Population density is the driving force. If there are too many organisms for the available resources bacteria reduce their reproductive rate. Across an evolutionary continuum that does not discount Creation, you can get from pheromonal communication in bacteria to pheromonal communication in primates, including humans -- and find many similarities along the way.

James V. Kohl
http://www.pheromones.com