Buchan’s biography tries to resurrect Smith’s reputation as a laissez faire economist. In particular, he says that the “invisible hand,” as a defining expression of Smith’s work, is not such at all because it’s used by Smith just “three times in the million-odd words of Adam Smith that have come down to us.” I’d say that this expression still captures - and captures well - Smith’s overarching theory, and that’s probably the reason it has had such currency.
Buchan starts out well by referencing Smith’s “The Theory of Moral Sentiments.” In that book, Smith says that we are not rational calculators who are driven by self-advantage, even at the expense of others if necessary. Rather, we are in Smith’s view sympathetic beings who, Hume-like, care about our interactions with others. It is true that each pursues their self-interest, but since we care via sympathy about what others think, we regulate ourselves to respect the interests of others as well as our own. In doing so, cooperation for mutual advantage is the norm, and it all works out for nations as well as individuals. Hence, with the emphasis on sympathy as the governing norm, there is this “invisible hand” at work that constitutes the essence of Smith’s theory.
The problem with Smith is Darwinian variability. We are not at all equal when it comes to the benign notion of sympathy. There’s not one human nature regarding this sympathy trait. There are, rather, twin poles of human nature. One pole is sympathetic other-regarding, much as Smith sees. The other is self-regarding only, void of sympathy. Both, as strategies, promote evolutionary survival. The former because one survives by being part of the group. The latter, combined with skill and strength, and deceit, succeeds by using others and the group for self-advantage. The problem with Smith’s theory is that the self-regard only tendencies, individually and when supported by group mores, unravel the benefits of cooperation, in favor of domination and manipulation. This is the reason for hierarchy, individually or collectively (e.g. white-based colonialism). While Smith, as Buchan points out, is well-intended and other-regarding by nature, his theory doesn’t match up so well with who we are from a Darwinian perspective.