A "Thereless" Existential Interrogative

Why	are	people
Cause: reason	Process: existential	Existent

(The title of the first chapter of Richard Dawkins' The Selfish Gene.)

Theme In A Declarative Projection Nexus

A certain amount of detachment	<< the learned Head of my chambers, Guthrie Featherstone, Q.C., M.P., says >> is essential to life as a barrister
Theme	Rheme

Theme In An Interrogative Projection Nexus

who	<< did	you	say >>	was	arrested
Theme	Rheme

See Halliday & Matthiessen (2014: 102).