The phenomenological evidence for distinguishing between REM and NREM sleep is overwhelming. However, this difference has only been found thanks to electrophysiological analytical methods, and is practically non existent in phenotypic terms, i.e., observable with the naked eye. It is well accepted that the selective pressure determining evolutionary changes can only work upon phenotypic differences. Hence, it follows that the differences between REM and NREM could not have been selected through evolution and this implies that, in functional terms, both states could be equivalent.
aLaboratori de Fisiologia, Universitat de les Illes Balears, 07071 Palma de Mallorca, Spain
bNICI/Department of Comparative and Physiological Psychology, University of Nijmegen, 6500 HE Nijmegen, The Netherlands
cLaboratorio de Biofı́sica. Departamento de Fisiologı́a, Universidad de la Laguna, 38320 Tenerife, Spain
Correspondence to: Ruben V. Rial Planas PhD, Laboratori de Fisiologia Animal, Edifici Guillem Colom, Universitat de les Illes Balears, Ctra. Valldemossa km 7.5, 07071 Palma de Mallorca, Mallorca, Spain. Phone: +34-971173147; Fax: +34-971173184
ABSTRACT