A study on the bacterium Pseudomonas aeruginous is analyzed because the bacterium has higher cognition and is unrelated to humans. These species communicate by quorum sensing (QS) where different cells produce small diffusible signal molecules, and monitor the concentration of these molecules in the local environment. Signals results of the different species confirmed that it was premature to make the conclusion that the results on the combinatorial communication were due to brain complexity because the researchers had not thoroughly explored whether similar combinatorial communication systems exist in other species.
Further analysis on the bacteria led to two analysis of chemically related N-acyl homoserine lactones, N-(3-oxododecanoyl)-L-homoserine lactone and N-(bu- tanoyl)-L-homoserine lactone (hereafter 3-oxo-C12-HSL and C4- HSL respectively) evidently used in quorum sensing. The studies showed that each signal independently regulates to a set of genes and that C4-HSL modulates the effect of 3-oxo-C12-HSL. Further, it was demonstrated that rhlRI system can have an activity independent of the lasRI system which were different from their separate effects. These studies confirmed that the effect of signal combinations differs from the sum of their effects in isolation.
In conclusion, the researchers identified linguistic communication as a special and important form of ostensive communication. They suggested that the most credible way of studying the topic is by comparisons with the cognitive mechanisms which make ostensive and linguistic communication possible, rather than with the surface form of the different communication systems.