Explain the evolutionary advantage of having multiple operons for various sugars

Operons are gene regulatory mechanisms that involve promoting and repressing genes that are involved in the metabolism of organic substances (i.e. sugars). Living organisms have the innate ability to metabolize glucose as the main source of energy. Although, in the absence of glucose, the organism must "learn" to use sugars other than glucose (such as lactose) in order to survive. 

For instance, in the lac operon:
In the absence of glucose, various regulatory proteins promote the transcription of the gene related to the metabolism of lactose. This will ultimately lead to the production of the enzyme beta lactosidase which will enable the organism to use lactose as energy in the absence of glucose. This will therefore increase the chances of the organism for survival and will be naturally selected for evolution.

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