Hard wired because children have shorter legs in comparison to the upper body; legs lengthen to adult proportions with the growth spurt at puberty. Long legs are a visual 'cue' of the female's sexual maturity, of her biological 'readiness' to mate. And high heels, of course, accentuate/exaggerate that ancient hard-wired visual cue - that's why people of both sexes find them irresistably sexy.

Now, shall we discuss why women wear lipstick? There's an ancient hard-wired 'visual cue' behind that one too, I've heard ...