Science often inspires science fiction writers to explore fantastic scenarios that may be just round the corner. However, sometimes, science fiction can also be an inspiration for science. One such inspiration for me was The Prestige by Christopher Priest, subsequently adapted into a movie by the same name by Batman director Chris Nolan. In this atmospheric story, rival Victorian magicians Robert Angier and Alfred Borden (played by Hugh Jackman and Christian Bale) engage in a bitter struggle to perfect the best magic trick. Borden creates an illusion where he walks into one cabinet on stage and immediately reappears from a second cabinet some distance away, defying the fundamental laws of physics. Angier, determined not to be out-classed, seeks out Nikola Tesla, the real life Serbian-American genius inventor of AC electric current, who builds him a machine that can duplicate matter. Angier now has the means to duplicate himself anywhere in the theater, thereby upstaging Borden's illusion. Currently, such machines are science fiction but without giving the plot away, if duplication were possible, it does raise some interesting questions about the nature of minds, bodies and unique individuals.

What if it were really possible to copy the body perfectly, right down to its exact molecular structure? Would the duplicated body have the same mind? Logic dictates that if the mind is a product of the brain, then two identical brains should produce two identical minds. Or maybe the mind is separate from the brain and therefore not dependent on the material body, which is more akin to the notion of souls? Duplication of the body would not then duplicate the mind. These are the sorts of questions that scientists address in "gedanken," or thought experiments to investigate human reason and intuition.

Metaphysical ponderings concerning the nature of authenticity and uniqueness have been considered since medieval philosopher Duns Scotus proposed the concept of "haecceity" -- a property of an object that confers unique identity. The question of duplicated bodies and minds also depends on whether we think our minds are separate from our bodies -- more commonly known as mind-body dualism, as contemplated by French philosopher René Descartes in the 17th century.

Even though most of us may be unfamiliar with these concepts, many consider ourselves unique and feel that an identical copy could not possibly have all the same thoughts, feelings and memories. When does this reasoning emerge? As a developmental psychologist interested in children's cognition, these sorts of questions intrigue me. However, young children are not so good at answering thought experiments which is why, with my colleagues Thalia Gjersoe and Paul Bloom, we set out to investigate the nature of minds, bodies and individuals using a technique based on The Prestige.

In our recently-published paper in Cognition, "Do children think that duplicating the body also duplicates the mind?" we presented second-graders with a scientific-looking machine that had two metal boxes that were wired with dials, lights, and switches. Experiments began by opening each box to reveal that both were empty, placing a toy in the first box, closing the door and then "activating" the machine. After a delay of several seconds, the second box spontaneously buzzed. At this point the experimenter opened both boxes to reveal an identical looking toy in both. When asked what happened, children spontaneously answered that the machine had copied the first toy and that both toys were the same.

What about bodies? We could not use humans, so we used a pet. After witnessing the duplication event several times, the child was then introduced to a live hamster and told it possessed three physical properties that could not be directly seen. It had swallowed a marble that was in its stomach, it had a blue heart and it also had a broken back tooth. We then engaged the hamster in three activities to induce mental states. We whispered the child's name into the hamster's ear, we showed the hamster a drawing that the child had produced just before the experiment began, and we asked the child to tickle the hamster.

We then placed the hamster in the first box and enacted the duplication scenario again. When each box was opened, the child saw two identical-looking hamsters (both were siblings from the same brood). The question of interest was whether children would think that both hamsters possessed the same physical and mental states. We asked of each hamster in turn whether they had a marble, broken tooth and blue heart to assess physical properties. We also asked if each hamster remembered the child's name, seeing the picture and being tickled.

Over five sets of studies, a familiar picture emerged. One-third of children said that the machine had failed to copy the original hamster and that the second hamster possessed none of the original hamster's properties. The remaining two-thirds thought properties were duplicated but these were significantly more likely to be the physical properties than the mental properties. That is, children were much more likely to say that the hamsters' physical properties had been copied than its mental properties.

One might conclude that this is unsurprising, as it was the first hamster that had experienced these events. However, children didn't show the same bias when we duplicated a video-camera and showed it even more strongly when we drew attention to the unique identity of the first hamster by giving it a name. This explains why naming our animals and treating them as individuals changes the way we think and feel about them.

Our studies show that both notions of unique individuals and mind body dualism are present in 5-to-6-year-old children even though it is unlikely they have been explicitly tutored in these philosophical issues. Maybe this intuitive way of thinking about unique individuals is at the heart of some of our adult attitudes concerning new scientific technologies that threaten to undermine the integrity of the individual. For example, most of us think human cloning is wrong and it is banned in many countries. President Obama said cloning is "dangerous, profoundly wrong and has no place in society." One wonders whether the repugnance that many feel towards cloning is partly fuelled by the importance of the unique self that we believe constitutes the fundamental basis of human identity. However, as we move increasingly from science fiction to science fact, we are going to continue to encounter scenarios that challenge what it means to be human.