This is the conclusion reached by leading sleep researcher, Jerry Siegel, after decades of sleep research. In a recent article in the New Scientist Siegel claims that the effects of sleep deprivation are actually quite small and certainly not enough to offset the potential danger of being asleep (watch out that lion is going to get you!). Evidence from the animal kingdom is surfacing all the time which increases our understanding of sleep. It appears that fur seals, like dolphins, sleep one hemisphere at a time when hunting at sea and experience no REM activity, but once back on land they revert to the more normal sleep patterns of other animals (i.e. both REM and NREM activity and whole brain sleep).Siegel suggests that the purpose of REM sleep may be just to keep the brain stem active. If an animal is sleeping one hemisphere at a time then the brain stem is constantly active. So the purpose of REM sleep is simply to permit periods of NREM sleep. This understanding brings us one step closer to understanding the purpose of sleep. But then we have to ask – why NREM sleep? Siegel agrees that NREM sleep may aid some biological processes (e.g. production of neurotransmitters) but again doubts that it performs any vital functions that can’t be achieved during relaxed wakefulness. If it was vital how can we explain the fact that bullfrogs never sleep and that dolphins perform as well on vigilance tasks after 5 days sleep deprivation.Increasing knowledge of the sleep patterns of different animals suggests that it is ecology rather than biology which explains sleep. Currently only 150 mammals out of a total of 5000+ have been studied and other animal groups have been studied even less. Siegel argues that, on the basis of the current knowledge, the only factor that explains all sleep patterns is that species sleep for as long as they can get away with. The little brown bat sleeps a massive 20 hours per day which shouldn’t happen if sleep was related to size, metabolic rate or danger. The one factor that explains its amount of sleep is the fact that the brown bat eats flies that comes out for a few hours each night. In other words, the bat sleeps because it can and can still survive. Siegel points out that animals are actually safer when asleep; being awake is riskier because you may get injured and may be noticed.Hmmm. But all of this doesn’t explain why I feel so rough after a bad night’s sleep.