In 1945, two sculptures meant to represent the average man called Norman and woman called Norma in the United States went on exhibit at the American Museum of Natural History. 

That same year, a contest was launched to find a living representation of Norma. Normal is often used to mean "typical", "expected", or even "correct". By that logic, most people should fit the description of normal. And yet, not one of almost 4,000 women who participated in the contest matched Norma, the supposedly "normal" woman.

This puzzle isn't unique to Norma and Norman, either — time and time again, so-called normal descriptions of our bodies, minds, and perceptions have turned out to match almost no one. So what does normal actually mean — and should we be relying on it so much?

In statistics, a normal distribution describes a set of values that fall along a bell curve (曲线). The average, or mean, of all the values is at the very center, and most other values fall within the hump (驼峰) of the bell. Normal doesn't describe a single data point, but a pattern of diversity. Many human traits, like height, follow a normal distribution. Some people are very tall or very short, but most people fall close to the overall average. Outside of statistics, normal often refers to an average like the single number pulled from the fattest part of the bell curve that excludes all the nuances of the normal distribution. Norma and Norman's proportions (比例) came from such averages.

Applied to individuals, whether someone is considered normal usually depends on how closely they get to this average. At best, such definitions of normal fail to capture variation. When limited or inaccurate definitions of normal are used to make decisions that impact people's lives, they can do real harm. There were examples in history.

To this day, people are often targeted and discriminated against on the basis of disabilities, mental health issues, and other features considered "not normal". But the reality is that the differences in our bodies, minds, perceptions, and ideas about the world around us — in short, diversity — is the true normal.