Because the notion of abnormal versus normal is so deeply engrained and so difficult to escape, another example is warranted. This one is facetious but it gets to the heart of the matter. Imagine we discover a new disorder, giantism. This disorder, which we will diagnose on the basis of height greater than 196 cm (6 feet 5 inches), has a frequency of 1 per cent. DNA differences found to be associated with giantism will also be associated with individual differences in height throughout the distribution – for short people as well as tall ones. The point is that height and its genetic basis are perfectly normally distributed. There is no abnormal, just the normal distribution with its normal extremes. It won’t help to create another diagnostic category of ‘almost a giant’. Why would we create a disorder of giantism when height is so clearly a continuous trait? It doesn’t make sense. I would argue that it is just as nonsensical to create distinct disorders for any problems – physical, physiological or psychological. They are merely the quantitative extremes of continuous traits.

Robert Plomin, Blueprint: How DNA makes us who we are, Cambridge, Massachusetts, 2018, p. 78