Full Idea
The pentathletes are the most beautiful, being at the same time naturally suited to both speed and force.
Gist of Idea
Pentathletes look the most beautiful, because they combine speed and strength
Source
Aristotle (The Art of Rhetoric [c.350 BCE], 1361b09)
Book Reference
Aristotle: 'The Art of Rhetoric', ed/tr. Lawson-Tancred,H.C. [Penguin 1991], p.89
A Reaction
This is still true. Watch the Olympics. The bodies we envy most belong to those who do a variety of disciplines. The most beautiful music fulfils a variety of functions (structure, as well as melody, drama, rhythm, harmony, novelty).