Broadly speaking, physical attractiveness has two sources. The first is innate beauty, generally arising from one’s genetic endowment. The other is external effort, in the form of exercise, good make-up, fashionable clothing. A person’s observed level of attractiveness is some function of both. So here’s the natural question, from an economic perspective: are innate beauty and external effort technical complements or technical substitutes?
If they are complements, having more of one should increase the return on the other. If they are substitutes, having more of one should decrease the return on the other. For example, for whom would a professional make-up job make the greatest difference – a beautiful woman or a homely woman? Say the make-up job turns the natural 8 into a 8.5, and the natural 4 into a 6. In that case, the homely woman benefits more (assuming a uniform attractiveness scale), and thus innate beauty and external effort are substitutes. The make-up makes up for what the homely woman doesn’t have, whereas its impact is more superfluous on the beauty. But if the make-up job turns the natural 8 into a 9.5 and the natural 4 into a 4.5, innate beauty and external effort are complements. The make-up can only enhance what’s already there.
Why does it matter? Because the answer will affect the distribution of attractiveness in the population. From a given initial distribution, based on innate beauty, complementarity will tend to spread the distribution wider. The natural beauties will find it worthwhile to make themselves yet more beautiful, while the less fortunately endowed will make less effort and allow themselves to go downhill. Substitutability, on the other hand, will tend to narrow the distribution, as those endowed with less natural beauty will work harder and thus narrow the gap. A question for readers: based on your observations, which is closer to the truth? Does the answer depend on the gender in question?
Most changes occur on the external effort margin. But we can imagine some changes on the innate beauty margin. Someone who suffers a disfiguring accident takes a negative shock to their innate beauty. And while plastic surgery might seem the most extreme version of external effort, in this context it is best seen as an attempt to enhance innate beauty (since plastic surgery does not require ongoing effort, but instead changes the baseline to which ongoing effort adds). These cases could provide potential tests of complementarity versus substitutability. To the extent the inputs are complements, the disfigured person should make less deliberate effort than before, the plastic surgery patient more than before. With substitutes, the reverse would be true.
If the rewards of attractiveness depend not merely on one’s own realized attractiveness but also on that of others, then strategic concerns come to the fore. But those will have to wait for a future post.
(Aside for serious econ nerds: In mathematical terms, the key figure is the cross-partial derivative, which shows how a change in one variable [natural beauty] changes the effect a change in another variable [external effort]. If the cross-partial derivative is positive, then greater natural beauty increases the return on external effort, so the inputs are technical complements. If the cross-partial derivative is negative, then greater natural beauty diminishes the return on external effort, so the inputs are technical substitutes.)