Birth Order and Personality

By John M Oldham MD

There’s a common viewpoint that one’s personality is determined, or at least heavily influenced, by one’s birth order. Are first-borns the lucky ones, pre-destined to be ambitious, responsible high-achievers and natural leaders? And is the “middle child” predictably more easygoing and adaptable, whereas the youngest child scrambles for attention and can be rebellious and difficult? These are commonly held beliefs and certainly we could all find examples that we might argue prove the point, but science wouldn’t back us up. In a recent piece in the Washington Post (https://www.washingtonpost.com/science/2026/10/06/your-sibings-dont-set-your-personality-it-can-change-throughout-life/), journalist Michael Coren argues that foreseeing your future based on birth order is “about as good as astrology.” He reviews a number of scientific studies using the “Big Five” model to track the development of personality and its stability, or lack of it, over time. It turns out that birth order ranks pretty low on the list of things that shape personality. The notions that the first-born has advantages, and that the youngest has to struggle to be heard, come from common family lore. But these differences are not inevitable, and they generally fade away by adulthood. More meaningful is one’s genetic profile, followed by the many powerful ways that experiences shape that inborn template, throughout the life cycle. (See my blog from February of this year.) In the book on which this website is based (The New Personality Self-Portrait), these principles are discussed at length, along with recommendations for those who wish to smooth out some rough edges of who they are.

Journalist Michel Coren summed it up well: “Our personalities are like landscapes: recognizable across the years, but steadily reshaped by the forces around us and, if we choose, by our own determined effort.”