Every mental activity — contemplating a theorem, savoring a hot fudge sundae, dreaming of the boy next door — consists of neurons firing in a certain… - Thomas Lewis

Loving is limbically distinct from in love. Loving is mutuality ; loving is synchronous attunement and modulation. As such, adult love depends critically upon knowing the other. In love demands only the brief acquaintance necessary to establish an emotional genre but does not demand that the book of the beloved’s soul be perused from preface to epilogue. Loving derives from intimacy, the prolonged and detailed surveillance of a foreign soul.

Arising somewhere between 100 million and 150 million years ago, monotremes demonstrate the beginnings of the departure from a reptilian way of life. Although it was far from obvious to early taxonomists, the feature that distinguishes mammals from reptiles is the appearance of a new brain within their skulls — the limbic brain. The echidna possesses not only nature’s most primitive uterus, but also her most primitive limbic apparatus. Of all mammals, echidnas alone lack one limbic process: they do not dream during sleep.

Proof that expressions are intrinsic is closer at hand than the South Pacific. As Darwin knew, a congenitally blind baby will smile while interacting pleasurably with his mother. Such a smile comes from a developing creature unable to speak, walk, or even sit up, but he already knows how to express happiness through a configuration of muscular contractions he has never seen on anyone’s face. His knowledge has to be innate.