As this scene from Arthur s Baby demonstrates, siblings Arthur and D.W. are practiced squabblers. They love each other, but the brother and sister from the Arthur series are poster children for theories about the influence of sibling birth order on personality.
Diversity reduces competition for scarce resources.
He goes on to explain how first born children tend to conform to authority, while second borns tend to rebel. Arthur plays reliable worrywart to D.W.'s drama-queen rebel. Arthur expects his parents to appreciate his competence and dependability, and resents the attention second-born D.W.'s antics command. D.W., four, can't compete with Arthur's skills, so she steals the spotlight at every opportunity, switching from charmer to brat with quicksilver timing. If her role is to threaten Arthur's status, his is to outsmart her and show her up as badly behaved.