Danger Avoidance: An Evolutionary Explanation of Uncanny Valley

From common sense one might be lured to think that as the appearance of synthetic agents, such as robots and computeranimated characters, approaches near to human appearance, they tend to be more interesting and likeable by humans. Although this intuition stands up to a point, it is not always the case. The concept of “Uncanny Valley,” a hypothesis put forth by the famous roboticist Masahiro Mori in 1970, gives an outline regarding human reaction toward human-like synthetic agents. It states that although with increasing humanlike attributes in appearance and motion, synthetic agents get more positive response from humans, after a certain point the emotional response becomes negative. The negative trend continues as long as the appearance and motion become indistinguishable from human beings; then the emotional reaction becomes similar to that toward the natural agents, i.e., human beings (Mori 1970). The presence of Uncanny Valley is visible in the plot of degree of familiarity/likeability of synthetic agent against anthropomorphism (Figure 1). Although the initial support for Uncanny Valley came anecdotally from mass media (e.g., negative audience response of computer-animated movies such as The Polar Express and The Final Fantasy: The Spirits Within), its presence was later supported by several experimental studies (Bartneck et al. 2007; Seyama and Nagayama 2007; MacDorman et al. 2009). Despite being an accepted psychological phenomenon, the precise reason behind this response is not well understood. Different theories have been proposed, such as mortality salience (MacDorman 2005), pathogen avoidance (Rozin and Fallon 1987), and cognitive dissonance related to facial aesthetics (Rhodes et al. 2001; MacDorman et al. 2009). Nevertheless, none of these theories explain the evolutionary basis of the presence of Uncanny Valley in spite of the phenomenon being conserved in other primates (Steckenfinger and Ghazanfar 2009). Even though the concept of pathogen avoidance (Rozin and Fallon 1987) can explain Uncanny Valley in an evolutionary sense to some extent, it cannot explain why a seemingly healthy human corpse, even a fresh one, generates strong negative emotions. Thus, we hypothesize the presence of Uncanny Valley as a general mechanism of danger avoidance instead of specific pathogen avoidance. We put forth the following arguments supporting our explanation. Many species are known to bury, hide, or otherwise isolate their dead members. Dead rodents are often found to be buried by their conspecifics (Misslin 2003). Similar behavior is also observed in social insects, such as ants (Wilson et al. 1958) and honeybees (Visscher 1983). These defensive responses are considered as a survival function in commensal species (Misslin and Ropartz 1981; Misslin 1982). Being cohabiting social animals, primates have also developed burial as a mechanism of separating the dead from the living (Spennemann 2007). This is thought to be one of the reasons that people find human-like response more important than appearance in robots (Dautenhahn et al. 2005). Necrophobia is deemed to be one of the reasons behind human burial practices at least since the early Iron Age (Saponetti et al. 2007). In prehistoric times, humans had an expected lifetime of around 25 years (Simon 1995). Thus, most deaths