While first-borns want to do things right, later-borns want to do things differently.

The second child carefully watches what position the eldest has claimed, then carves out a distinct niche.

If the first-born shines in math, tennis and violin, the second may pursue art, guitar and skateboarding. In the world of Nobel Prize laureates, first-borns are over-represented in science, later-borns in literature.

While first-borns are eminently accomplished and capable, the more unconventional later-borns are historically the ones responsible for grand revolutionary advances that drive societal change. It's later-borns who fought for equality, freedom of speech, freedom of worship and abolition of slavery, says Sulloway, author of Born to Rebel: Birth Order, Family Dynamics and Creative Lives. Mother Teresa, Darwin and Gandhi were all later-borns.

The arrival of a third child automatically creates a middle one, and middle children can be difficult to categorize - which is fine by them, since in forging their identity they actively avoid being boxed in.

Middles - whether the second of three, the second and third of four, or the middle five of seven-usually are in the fewest photos in the family album. Receiving less one-on-one time from parents, middles form attachments with their peers, often developing extensive networks of friends.

While they may deeply love their family, they're the most likely to move far away from home, the least likely to care about family genealogy, and the best prepared for life's vicissitudes. John F. Kennedy, Robert Kennedy, Madonna, Jean Chrétien and Avril Lavigne are all middle children.