There's a good article on the circle in the NY Times, which uses Vasily Kandinsky as a jumping off point.
This being December, I’d like to honor Kandinsky through his favorite geometry, by celebrating the circle and giving a cheer for the sphere. Life as we know it must be lived in the round, and the natural world abounds in circular objects at every scale we can scan. Let a heavenly body get big enough for gravity to weigh in, and you will have yourself a ball. Stars are giant, usually symmetrical balls of radiant gas, while the definition of both a planet like Jupiter and a plutoid like Pluto is a celestial object orbiting a star that is itself massive enough to be largely round.
On a more down-to-earth level, eyeballs live up to their name by being as round as marbles, and, like Jonathan Swift’s ditty about fleas upon fleas, those soulful orbs are inscribed with circular irises that in turn are pierced by circular pupils. Or think of the curved human breast and its bull’s-eye areola and nipple.
Our eggs and those of many other species are not egg-shaped at all but spherical, and when you see human eggs under a microscope they look like tranquil suns with Kandinsky coronas behind them.
Full article here.