In yesterday's New York Times, science columnist John Tierney notes that the gesture of the upturned palm, "signifying 'Gimme,'" is "one of the oldest and most widely understood signals in the world." He claims it's "activated by neural circuits inherited from ancient reptiles that abased themselves before larger animals":
The palm-up gesture is what the anthropologist David Givens, director of the Center for Nonverbal Studies in Spokane, Wash., calls a "gestural byproduct" of the circuits in the brain and spinal cord that protected vertebrates hundreds of millions of years ago.
Confronted with a threat, ancient lizards would instinctively bend their spine and limbs to press their bodies closer to the ground, protecting the neck and head and signaling submission to a larger animal. This crouch display is the opposite of the high-stand display, the aggressive posture of a stallion or a gorilla raising its chest and head to appear larger.
The human remnant of the crouch display is a shrug of the shoulders, which lowers the head and rotates the forearms outwards so that the palms face up. Conversely, the high-stand display persists in humans as a rotation of the forearms and palms in the opposite direction, producing the domineering palm-down gesture used by a boss slapping the conference table or an orator commanding quiet from his audience.
I'm no anthropologist, but I always thought the palm-up gesture came from holding out your hand so that the person from whom you want something can put it there. That, at least, is what I have in mind when I ask someone for some cash or the salt. Isn't it more plausible to suppose that the metaphorical meanings of the gesture evolved from its use by creatures that hold things in their hands than to think we're echoing the submissive displays of lizards?