Editor's Note: The following is an excerpt from the 1999 book The Science of Star Wars by Jeanne Cavelos.

The most amazing thing about R2-D2 (Artoo) and C-3PO (Threepio) is how human they seem. They each have strong personalities, and they constantly convey emotions. Threepio is a worrier and a whiner. He seems constantly irritated, often venting his emotions by insulting Artoo, calling him an "overweight glob of grease" and other colorful insults. Artoo can be excited, as when he discovers Princess Leia is a prisoner on the Death Star; embarrassed, as when he falls from Luke's X-wing into the swamps of Dagobah and whistles casually to cover; and he can be stubborn, as he is when Yoda tries to take a small flashlight from Luke's camp.

Assuming we could give computers and robots human-type emotions and personalities, why would we want to? In science fiction, emotional computers and robots usually end up wreaking havoc. In 2001: A Space Odyssey, the Hal 9000, which has the ability to perceive the emotions of others and express his own, kills all but one of the spacecraft's crew, and expresses fear as the remaining astronaut turns him off. In these cases, and in life, emotion is often perceived as negative. Too much emotion in a person or a robot can lead to irrationality or psychosis. Decisions made out of emotion are considered unwise. Most people believe robots should be rational, logical, and scientific, unaffected by emotion. Yet some scientists argue that while too much emotion can cause irrational behavior, so can too little.

Evidence of the importance of emotions has been found by Dr. Antonio Damasio, M. W. Van Allen Professor of Neurology at the University of Iowa College of Medicine and author of Descartes' Error. Dr. Damasio treats patients with frontal lobe disorders. In these patients, communication between the neocortex and the limbic system is impaired, giving Dr. Damasio an opportunity to study how humans function when logic and emotion are not intertwined. The patients seem extremely logical and intelligent, yet unemotional.

You might think such people would act very rationally. And sometimes they do. Dr. Damasio relates the story of one patient who drove to the doctor's office over treacherous roads after an ice storm. With complete calm, the patient navigated the slick roads, utilizing the appropriate methods for dealing with icy conditions. The woman driving in front of him skidded on the ice, reacted inappropriately by braking, and spun into a ditch. While most of us would have reacted to her skid in fear and perhaps hit the brakes ourselves, the patient had no such reaction, continuing sedately on his way, following the correct procedures. Here, the patient's unemotional state worked to his advantage, much like we imagine a computer's unemotional state to work to its advantage.

Yet in actuality this lack of emotion is more often a hindrance than a help. Dr. Damasio relates another story of the same patient. The doctor suggested two possible dates for their next appointment, and the patient then spent nearly a half hour discussing the pros and cons of each date, covering every possible circumstance, factor, option, and consequence: other appointments, other commitments, the cost of gas, the weather, and on and on. The doctor finally cracked and picked a date himself.

Most of us, after a brief indecision, would choose an option. We would decide one factor outweighed the others, or if there was little difference, we would go with a gut feeling that one option was better than the others, or we would choose something at random. We would know that any prolonged consideration of this minor issue would be a waste of time, and embarrassing as well. Those negative emotional associations would keep us from debating the issue at such length. Yet those negative associations did not play a part in the patient's actions. In this case, the patient's unemotional state crippled his ability to make a simple decision.

If a robot is flying your spaceship, you certainly don't want it "slamming on the brakes" in a panic when this could create a dangerous condition. Yet you also don't want it endlessly debating whether it would be better to visit Obi-Wan on Tatooine first and then go to Coruscant, or vice versa. Both Threepio and Artoo seem able to set priorities, remain focused and motivated, make decisions, and interact rather effectively with humans, which suggests that they do have emotions.