Biodiversity differentiation and the relative importance of forces and causes driving evolution at the molecular and organismal levels require more critical testing. The opposite slopes of Lower Nahal Oren, Mount Carmel, Israel, designated 'Evolution Canyon', display dramatic biotic contrasts. Higher solar radiation on the south-facing slope (S-slope) makes it spatiotemporally more heterogeneous, warmer, drier and fluctuating than the north-facing slope (N-slope). Consequently, local biodiversity differentiation across several hundred metres displays globally divergent patterns. In different groups of organisms (i.e. across phylogeny) the 'tropical Asian-African' S-slope harbours African and Asian xeric tropical biota. The S-slope is richer on average in terrestrial species, displaying higher genetic diversity than the 'temperate European' N-slope, which is richer in aquatic-dependent taxa. Adaptive differences in different organisms are demonstrated within and between the slopes. Microclimatic aridity diversifying selection seems here a major evolutionary force that drives adaptive molecular and organismal evolution. Present results suggest that 'Evolution Canyon' provides a fertile local testing model of evolutionary predictions.