Prostaglandin D synthase (beta-trace protein): a molecular clock to trace the origin of REM sleep?

In 1965, Zuckerkandl and Pauling proposed a novel concept that some important molecules termed semantides, which carry the information of the genes or a transcript thereof, can be used as molecular clocks to trace evolutionary history. According to this concept, enzymes are designated as tertiary semantides, following genes (primary semantides) and the mRNA (secondary semantides). Based on this idea, I propose that prostaglandin D synthase (which has been demonstrated recently as identical to the beta-trace protein present in the cerebrospinal fluid of mammals) may serve as a molecular clock to trace the origin and evolution of rapid eye movement sleep in the vertebrates.