Apparently the difference between A's and B's is linked to variations in circadian rhythms which control our body temperature, hormone levels, heart rate and sleeping-waking cycles. Moreover, Professor Jim Horne, a sleep researcher and expert from the Loughborough Sleep Research Centre in the UK defnes A's as 'larks', and B's as 'owls', with the latter being more suited to shift work and coping with jet lag. Owls work best in the afternoon and evening. For further reading and to access the 'Are you a lark or an owl test' get hold of a copy of Professor Jim Horne's Sleepfaring: A Journey Through the Science of Sleep (2006), Oxford University Press, Oxford.
These theories go a long way to explaining the differences between Jozef's and my own work habits and energy cycles. I've always classified myself as a morning person (and indeed I usually wake up around 6am and want to do the bulk of my work prior to or just after lunch) whereas Jozef prefers a late start and doesn't kick in creatively so to speak until mid afternoon. He is also more prone to doing all-nighters to get his work done. The compromise we've come to is to start our business meetings and our brainstorming sessions at lunch time and to go beyond the standard 5pm work day, although I do privately lament the loss of three hours in the am. But hey – that's the sprightly singing lark in me!