He is best known for his claim that birth order exerts large effects on personality, and the subsequent debates about this issue. In his 1996 book Born to Rebel, Frank Sulloway suggested that birth order had powerful effects on the Big Five personality traits. He argued that firstborns were much more conscientious and socially dominant, less agreeable, and less open to new ideas compared to laterborns.
Frank Sulloway is most recognized for his claim that birth order significantly influences personality, leading to ongoing discussions about this subject. In his 1996 book "Born to Rebel," he proposed that first-born children tend to be more conscientious and socially dominant, while less agreeable and open to new ideas compared to later-born individuals.