In the phylogenetic history of photosynthesis the C4 photosynthetic pathway is a rather latě, a nearly recent event. With the background of globál CO2 starvation and given the evolutionary competence, different ecological constraints as water and/or nitrogen deficiency oř salinity could be the driving forces in distinct habitats for selection of genotypes with a CO2 pump. Whether C3-like C3-C4 intermediate species BLS Moricandia arvensis with a less efficient CO2 pump are on the way to C4 photosynthesis remains an open question. Selection for a somewhat improved CO2 concentration mechanism under strong selective pressure seems to be a possible experimental approach to imitate evolutionary steps in adaptation to CO2 starvation.