Is Empathy Unique to Humans?
Many animals certainly sympathize with each other's distress or danger (Darwin, 1982; 1871, p. 77).
Given the evolutionary advantage of empathy, and the evolutionary continuity between humans and apes (our closest living relative), it would be unwise to assume that empathy is unique to humans and is not a capacity held by apes (de Waal, 2008). Furthermore, recent evidence suggests that empathy is not unique in humans and apes but, instead, may be a capacity held by other animals (Bartal, et al., 2011; Edgar, Lowe, Paul, & Nicol, 2011; Plotnik, de Waal, & Reiss, 2006; Reiss & Marino, 2001).
Emotional contagion can be seen whenever a bird startles and the entire flock of birds automatically take flight without any knowledge of the initial trigger (de Waal, 2008). Yawn contagion (a manifestation of the emotional contagion system) has been reported in many animals such as chimpanzees (de Waal, 2008) and dogs (Joly-Mascheroni, Senju, & Shepherd, 2008).
Furthermore, pet cats and dogs have been found to react with sympathetic concern, such as laying their head in the lap of the distressed person, when a family member feigns distress such as crying or choking (Zahn-Waxler, Hollenbeck, & Radke-Yarrow, 1984). Moreover, this consolation response is not just displayed by dogs toward family members, but has also been demonstrated in dogs toward distressed strangers (Custance & Mayer, 2012). Moreover, rhesus monkeys have been found to refuse to pull a cord that results in them receiving food if the cord also results in electric shock to a companion monkey who subsequently displays a pain reaction (Masserman, et al., 1964; Wechkin, Masserman, & Terris, 1964).
It is unclear, however, whether such sympathetic responses reflect true concern for others or an attempt to alleviate aversive vicarious arousal (de Waal, 2008).
As for cognitive empathy, after almost four decades of research (Menzel, 1974), current consensus is that apes show at least some level of empathetic perspective taking (de Waal, 2008). Such perspective-taking relies on the developmental shift from a self-oriented to social perspective such that one is able to infer mental states in others (Gallup, 1982). The ability to infer another's mental state is an indicator of self-awareness and a manifestation of such self-awareness is the capacity to recognise one's own body reflected in a mirror (Bischof-Kohler, 1991; Johnson, 1982; Zahn-Waxler, et al., 1992).
While there are many studies demonstrating mirror self-recognition in humans (Bischof-Kohler, 1991; Johnson, 1982; Zahn-Waxler, et al., 1992) and apes (Anderson & Gallup, 2011; Gallup, 1970; Povinelli et al., 1997; Povinelli, Rulf, Landau, & Bierschwale, 1993; Suarez & Gallup, 1981; Walraven, van Elsacker, & Verheyen, 1995), emerging evidence suggests that bottlenose dolphins (Reiss & Marino, 2001) and Asian elephants (Plotnik, et al., 2006) also share this important capacity.
Bottlenose dolphins and elephants are phylogenetically distant from apes and humans (Reiss & Marino, 2001); that is, their evolutionary line diverged long ago from the primate lineage. Thus, an implication of the finding that bottlenose dolphins and elephants also possess the ability of self-recognition is that empathy may not be attributable to factors specific to apes and humans (Reiss & Marino, 2001). Rather, a characteristic common to bottlenose dolphins, elephants, apes, and humans is that they all possess a large brain size relative to body size (called encephalization). Consequently, empathy may be attributable to high encephalization (Reiss & Marino, 2001).
High encephalization has long been correlated with improved cognitive abilities (Lefebvre, Reader, & Sol, 2004). Because cognitive empathy is believed to be depend on high cognitive abilities (Call & Tomasello, 2008), one could hypothesise that any animal with high encephalization may be capable of empathy. While it has long been recognised that rodents exhibit emotional contagion (Langford et al., 2006), rodents also have high encephalization (Herculano-Houzel, 2007). Could it be that rodents are capable of true empathy?
Research suggests that, indeed, this is the case. In a series of sessions, researchers (Bartal, et al., 2011) placed a rat in an enclosure with another rat trapped in a clear restrainer in the centre of the arena. The free rats learned to open the restrainer to allow the trapped rats to escape. Why did the rats free their cagemates?
One explanation derives from learning theory whereby free rats may have learned to liberate the trapped rat in order to gain some reward. Indeed, free rats spent more time near the trapped rat than any other area of the enclosure, and contacted the trapped rat through holes in the restrainer, suggesting that social contact was desired. Yet, free rats learned to open the restrainer door without any training or reward (Bartal, et al., 2011). Moreover, free rats opened the restrainer door even when the liberated rat could only exit into a separate enclosure, preventing social interaction and, thus, eliminating the expectation of social contact as a motivator to door opening behaviour (Bartal, et al., 2011).
An alternative explanation is emotional contagion. As the trapped rat issued alarm calls, it may have been that the free rat's behaviour was motivated by an attempt to reduce its own distress at the alarm calls. This explanation is supported when considering that free rats did not open empty restrainers or those holding inanimate objects. Yet, when a second restrainer containing chocolate chips was added to the enclosure, the free rats opened both restrainer doors and shared the chocolate with the liberated rat (Bartal, et al., 2011).
Although this does not preclude emotional contagion as the motivation behind opening the cagemate's door, the researchers concluded that the alarm calls were too infrequent for this to be a viable explanation. Furthermore, the sharing behaviour of free rats implies an extra dimension of pro-social behaviour. Specifically, when free rats were placed in an enclosure with two restrainers (one with chocolate chips and one that was empty), the free rats ate virtually all the chocolate upon opening the door. However, in sessions that held a trapped rat in the second restrainer, the free rats ate fewer chocolate chips, sharing the food with the liberated rat (Bartal, et al., 2011). Therefore, the results suggest that the rats demonstrated targeted helping as a manifestation of empathetic perspective taking. Consequently, the results suggest that empathy is biologically derived (Bartal, et al., 2011).
So, if empathy is biologically derived and attributable to high encephalization, animals that do not have a large brain size relative to body size should not be capable of empathy. Or are they? Chickens do not have high encephalization (Jerison, 1985) yet hens have been found to exhibit increased alertness, decreased preening behaviour, and a reduction in eye temperature in response to their chicks stress at exposure to puffs of air (Edgar, et al., 2011).
These physiological and behavioural changes in response to their chick's stress were taken as signs of empathy and, thus, this research suggests that chickens possess the foundations of empathy.
Further research, however, has found that hens do not exhibit such responses towards unrelated but familiar hens (Edgar, Paul, Harris, Penturn, & Nicol, 2012). This is an important point because it shows that whether an animal is considered to possess empathy depends not only on how empathy is defined (that is, as an automatic emotional response, as a higher cognitive process, or both), but other factors such as to whom the empathy is directed (offspring, familiar other, or stranger) and what tasks are used to measure empathy (physiological responses or behavioural responses).
