Name: Chronotypes. Age: The word was coined in the 1970s. What does it mean? Literally, time type. What’s that? It’s a concept in sleep psychology. A chronotype describes your “circadian typology or the individual differences in activity and alertness in the morning and evening”. Circadian? A 24-hour cycle. It’s your body clock. Sleep psychologists reckon they can determine our natural sleeping patterns. By understanding our own, we can have a happier, more productive life. Sounds a bit simplistic. Perhaps. But sleep is big business these days – one in three people are believed to experience sleep deprivation – and everyone is keen to latch on to the latest fashionable theory. And what is the latest fashionable theory? That there are four basic chronotypes, each of which has been assigned an easy-to-remember animal name. Larks, owls, roosters? That sort of thing, though the psychologists have moved on from bird life. The Australian sleep expert Olivia Arezzolo is plugging what is fast becoming the new orthodoxy: bears, wolves, lions and dolphins. Can you describe the sleep characteristics of each animal type? Well, bears account for more than half the population. Rather boringly, they follow the solar cycle, rising with the sun and winding down in the evening. They also tend to be useless immediately after lunch. Nothing to do with large men with beards and tattoos? That’s a different type of classification. Ah yes. Wolves prefer to get up late and are more energetic at night. So not a great time to be a wolf. Not with pubs and restaurants shutting at 10pm. What about the others? Lions get up early, work furiously in the morning, tail off after midday and are in bed just as the wolves are coming out to play. And dolphins? The most unfortunate category of all: poor sleepers who are often irritable and find it hard to work in the afternoon. Arezzolo says they account for 10% of the population. What jobs can they do? She suggests something entrepreneurial to match the dolphin’s short attention span and dodgy time management, though prime minister may also be an option. Are real dolphins poor sleepers? They are very light sleepers. Only half their brain is asleep at any one time – “unihemispheric sleep” – so they can carry on breathing and watch out for predators. They sleep with one eye open. How extraordinary. That’s the natural world for you. Can you change your chronotype? No, but a healthy diet, less booze, some meditation and hiding your mobile phone will help give you a better night’s sleep, regardless of your animal type. Do say: “To sleep, perchance to dream – ay, there’s the rub, unless you happen to be a dolphin, of course.” Don’t say: “Zzzzzzzzzzzzzzz.”