If a sleep doctor is to be believed we 7.4 billion people can be grouped under four categories represented by four animals - bears, wolves, lions and dolphins.

This report by Business Insider quotes extensively from Dr. Michael Breus, a sleep doctor. The doctor says that human beings have an internal clock that is different for different people. The study of internal clocks is known as chronobiology.

He categorizes human beings into four groups named after the four animals mentioned earlier. According to him the bears are the largest group accounting for half the population. The other groups represent roughly 17% of the population each.

The internal clock in the bears group follows the movement of the sun. The bears typically rise at 7 a.m. and sleep by 11 p.m. They require their full quota of 8 hours of sleep.

The members of the dolphin group have an internal clock that wakes them up at 6.30 a.m. and puts them to sleep by 11.30 p.m. They are typically light sleepers and may even be insomniacs.

The group that wakes up early full of energy is the Lions group due to the internal clock present in them. However, they get exhausted by late evenings.

The really late risers are the wolves group. Their internal clock gives them a difficult time to wake up. However, as the day wears on they become more energetic towards the evenings. They go to sleep often beyond midnight.

Dr. Breus, in his website, explains that several biological clocks are present in each human being's brain and body. He tries to suggest ways and means of working with the body after he determines the human being's chronotype.

He urges people to take his quiz to determine the chronotype. Based on the group that you belong to, he offers suggestions on when to do certain activities and when not to do certain activities.

What Dr. Breus recommends is that you should adjust your daily routine to match the biological rhythm you possess.

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