Upper Paleolithic people developed strategies to reduce their fuel requirements as many people have done since (including ourselves in recent years). In southwestern France (displayed here) 75 percent of known Upper Paleolithic sites are located on south-facing slopes and at the bases of south-facing cliffs. This familiar strategy is based on the recognition that, at European latitudes, south-facing embankments and cliff faces take on solar heat during the day and give if off slowly at night. Of course, south-facing places are also drier because of higher evaporation rates.