The import of nutriments over their cellular membranes is one of the main tasks of all living cells. Even though a major part of the cell's molecular machinery is devoted to this task, principles of selective membrane transport are not yet well understood, mainly due to the fact that the membrane proteins responsible are notoriously difficult to resolve in their structure, the latter a prerequisite for a full physical description of the function. Recently, cell biology got very lucky in having the structures of two closely related membrane proteins solved. Two highly homologous aquaporins from the same bacterium, Eschericha coli, have become structurally known: one that conducts only water, called AqpZ, and one that conducts water as well as the nutriment glycerol, called GlpF. The discoveries have permitted us through structure analysis with VMD and molecular modeling with NAMD to look over nature's shoulder in the evolutionary design of two similar import channels of different conductivity. As described in a recent paper and on our aquaporin site, in making a water channel also a glycerol channel, nature has turned to a very basic principle, namely adjusting the overall pore size of the channel from a very narrow channel, just wide enough for water, to one wide enough also for glycerol.