Rand introduces a theory of sex in Atlas Shrugged that is purportedly implied by her broader ethical and psychological theories. Far from being a debasing animal instinct, sex is the highest celebration of our greatest values. Sex is a physical response to intellectual and spiritual values - a mechanism for giving concrete expression to values that could otherwise only be experienced in the abstract.
One is sexually attracted to those who embody one's values. Those who have base values will be attracted to baselessness. Those who lack any clear purpose will find sex devoid of meaning. People of high values will respond sexually to those who embody high values.
That our sexual desire is a response to the embodiment of our values in others is a radical and original theory. However, even those who are sympathetic to this theory have criticized it as being incomplete.
This sexual theory is illustarted in the contrasting relationships of Hank Rearden with Lillian Rearden and Dagny Taggart, and later with Dagny Taggart and John Galt. It is presented symbolically via the bracelet.
Important illustrations of this theory are found in:
Section151 - recounts Dagny Taggart's relationship with Francisco d'Anconia.
Section161 - recounts Hank and Lillian Rearden's courtship, and Lillian's attitude towards sex.