Significance
In the midst of rapid globalization, the peaceful coexistence of cultures requires a deeper understanding of the forces that compel prosocial behavior and thwart xenophobia. Yet, the conditions promoting such outgroup-directed altruism have not been determined. Here we report the results of a double-blind, placebo-controlled experiment showing that enhanced activity of the oxytocin system paired with charitable social cues can help counter the effects of xenophobia by fostering altruism toward refugees. These findings suggest that the combination of oxytocin and peer-derived altruistic norms reduces outgroup rejection even in the most selfish and xenophobic individuals, and thereby would be expected to increase the ease by which people adapt to rapidly changing social ecosystems.
Abstract
Never before have individuals had to adapt to social environments defined by such magnitudes of ethnic diversity and cultural differentiation. However, neurobiological evidence informing about strategies to reduce xenophobic sentiment and foster altruistic cooperation with outsiders is scarce. In a series of experiments settled in the context of the current refugee crisis, we tested the propensity of 183 Caucasian participants to make donations to people in need, half of whom were refugees (outgroup) and half of whom were natives (ingroup). Participants scoring low on xenophobic attitudes exhibited an altruistic preference for the outgroup, which further increased after nasal delivery of the neuropeptide oxytocin. In contrast, participants with higher levels of xenophobia generally failed to exhibit enhanced altruism toward the outgroup. This tendency was only countered by pairing oxytocin with peer-derived altruistic norms, resulting in a 74% increase in refugee-directed donations. Collectively, these findings reveal the underlying sociobiological conditions associated with outgroup-directed altruism by showing that charitable social cues co-occurring with enhanced activity of the oxytocin system reduce the effects of xenophobia by facilitating prosocial behavior toward refugees.
At this time, we are witnessing one of the largest movements of refugees since the end of World War II (1, 2). Ongoing conflicts, persecution, and poverty in the Middle East and Africa have continued forced displacement of more than 65 million people since 2015 (2). Accommodating the large influx of migrants not only challenges the humanitarian capacities of European countries but also requires their native populations to adjust to rapid growths in ethnic diversity, religious pluralism, and cultural differentiation. However, the impetus to adapt to changing social ecosystems is susceptible to considerable interindividual heterogeneity (3). Resistance to this transition often goes along with xenophobic sentiment (4), and as a consequence, recent elections in Europe have favored populist candidates who have openly expressed xenophobic attitudes toward refugees (5). However, at the same time, volunteer work for migrants in the hosting countries has reached all-time highs and is estimated to exceed 1.6 million hours per month in Germany alone (6). In the face of growing tensions over differences in ethnicity, religion, and culture (3), there is an urgent need for devising strategies for helping foster the social integration of refugees into Caucasian societies.
As a result of evolutionary selective processes, humans possess a genuine propensity to contrast ingroup members (“us”) from outgroup members (“them”) (3). This dichotomy is adaptive, as ingroup members could not have survived and reproduced without altruistic cooperation [i.e., the goodwill and reciprocity of other ingroup members (7, 8)]. Only recently has neuroscience begun to dissect the biological components of altruistic cooperation and identified oxytocin (OXT), an evolutionarily conserved peptide signaling pathway originating in the mammalian hypothalamus (9), to be a key modulator (10). These insights could be gained because intranasally administered OXT (OXTIN) penetrates the brain (11⇓–13) and alters measures of neural and behavioral response (14). Specifically, OXTIN has been revealed to enhance social cooperation (15), generosity (16), and empathy (17, 18); to induce an altruistic response bias away from nonsocial toward social priorities (19); and to reinforce parochial preferences for outgroup hostility and ingroup centricity (20, 21). Consistent with the latter are findings from field studies of wild chimpanzees showing that heightened endogenous release of OXT correlates with greater ingroup cohesion during intergroup conflict (22). Furthermore, OXTIN facilitates social norm conformity (23⇓–25). Social norms, and personally costly sanctions against defectors of these norms, an inclination defined as altruistic punishment, may have evolved to protect ingroup biases from erosion through selfish motives (26⇓⇓–29).
The biblical parable of the Good Samaritan (Luke 10:25–16:17) describes an ethical maxim of helping strangers who have fallen in need. As such, it not only captures the essence of altruistic behavior by emphasizing the personal costs of selflessness toward others but also represents a formidable example that norm-enforced altruistic cooperation is by no means limited to the ingroup, but can even extend to outgroup members in ways neither precisely understood nor systematically researched. Here, we hypothesize that normative incentives co-occurring with enhanced activity of the OXT system exert a motivational force for inducing altruism toward strangers even in the most selfish and xenophobic individuals. To specifically test this hypothesis, the present study was devised to examine social norms, administered in the presence vs. absence of a norm-enforcing treatment with OXTIN, for their efficacy to promote altruistic responses in subjects scoring high on a xenophobia inventory (Xi).
Experiment 1
To this end, the rationale of Experiment 1 was to generate normative cues for altruistic responding toward refugees, on the basis of an incentivized donation task framed in the context of Europe’s refugee crisis (Materials and Methods). This paradigm was composed of 50 authentic case vignettes briefly describing the personal needs of poor people, half of which were portrayed as refugees (outgroup) and half as natives (ingroup), respectively. The personal needs comprised those elements the United Nations has defined as minimum standards for leading a safe and dignified life (30); that is, access to food, adequate housing, or participation in social and cultural life (31, 32). Assignment of cases to ingroup vs. outgroup frames was balanced across participants to rule out systematic bias. Subjects were endowed with EUR 50 and could donate a maximum of EUR 1 to each case, leaving them the rest (EUR 0–50) as personal payoff. Before testing, subjects’ prejudicial attitudes toward refugees was assessed by measuring their individual Xi index (33) (Materials and Methods). In Experiment 1, a total of 76 healthy female (n = 53) and male (n = 23) undergraduate students (mean age ± SD, 21.2 ± 3.0 y) completed the donation task. For the purpose of generating an altruistic norm, subjects were assembled in a lecture hall, enabling reputation pressures to prompt potential donors to respond more generously. Indeed, results show that participants contributed more than 30% of their endowment. Interestingly, the donations devoted to refugees were 19% higher (EUR 8.03 ± 6.74) than those to natives [EUR 6.71 ± 6.86; t(75) = 5.35; P < 0.01; d = 0.19]. This bias indicates an altruistic preference for the outgroup and was lowest in Xi high scorers (r = −0.34; P < 0.01) (Fig. 1A). An additional analysis including gender as a between-subject variable showed that neither the donations to natives and refugees nor the outgroup bias (donations to refugees minus donations to natives) was influenced by gender (all P ≥ 0.86).
The sociobiological conditions that reduce the effects of xenophobia by facilitating prosocial behavior toward refugees. (A) In Experiment 1 (n = 76), altruistic donations for the outgroup were lowest in those scoring high on the Xi index (scores ranging from 1 = low to 10 = high). (B) In Experiment 2, an independent sample of 107 male participants received OXTIN (n = 51) or placebo (n = 56) before the donation task. OXTIN promoted a 68% (outgroup) and an 81% (ingroup) increase in the donated sums. (C) Based on the subjects’ Xi scores from the 7-item scale of the realistic threat inventory, the sample was median-dichotomized (n = 54 Xi low scorers; n = 53 Xi high scorers). Xi low scorers who received OXTIN (n = 26) more than doubled their donations to both groups, whereas the peptide did not induce generosity in Xi high scorers (n = 25). (D) Pairing OXTIN with peer-derived norms in Experiment 3 prompted Xi high scorers to increase their outgroup-related donations by 74%. OXTIN + Norm, intranasal oxytocin paired with a peer-derived norm; PLCIN + Norm, intranasal placebo paired with a peer-derived norm. Error bars indicate the SEM. #P = 0.056; *P < 0.05; **P < 0.01.
Experiments 2 and 3
Experiments 2 and 3 were carried out within the same randomized controlled trial and involved an independent sample of 107 male participants (mean age ± SD, 24.1 ± 3.2 y). Before testing, their prejudicial attitudes toward refugees were measured by the Xi index (33). Subjects self-administered a 24-IU dose of OXTIN or placebo (PLCIN), which was instructed and supervised by a blinded experimenter in accordance with the latest standardization guidelines (34). Subsequently, subjects were placed alone in separate test cubicles and tested on the donation task established in Experiment 1 (Fig. S1). Based on the subjects’ Xi index, the sample was median-dichotomized, resulting in n = 53 Xi high scorers and n = 54 Xi low scorers. A repeated-measures analysis of variance with the between-subjects factors treatment (OXTIN, PLCIN) and Xi index (low, high), the within-subjects variable “frame” (ingroup, outgroup) and the donated sums as a dependent variable yielded main effects of treatment [F(1,103) = 4.64; P = 0.03; η2 = 0.04], Xi index [F(1,103) = 13.51; P < 0.01; η2 = 0.12], and frame [F(1,103) = 24.70; P < 0.01; η2 = 0.19]. Specifically, OXTIN promoted generosity toward both the outgroup [OXTIN, EUR 4.41 ± 5.73; PLCIN, EUR 2.62 ± 3.00; t(73.90) = 2.00; P = 0.05; d = 0.40] and the ingroup [OXTIN, EUR 3.62 ± 5.44; PLCIN, EUR 1.99 ± 2.58; t(69.88) = 1.94; P = 0.06; d = 0.39], evident in a 68% (outgroup) and an 81% (ingroup) increase in the donated sums (Fig. 1B). Furthermore, we detected an interaction of frame and Xi index [F(1,103) = 12.15; P < 0.01; η2 = 0.11]; that is, irrespective of OXTIN treatment, Xi low scorers’ contributions were 31% larger for the outgroup than for the ingroup [t(53) = 4.99; P < 0.01; d = 0.22], which replicates the outgroup favoritism observed in Experiment 1. As expected, this outgroup bias was absent in Xi high scorers, whose donations were not significantly different between the two frames [ingroup, outgroup; t(52) = 1.43; P = 0.16; d = 0.09]. An additional interaction of treatment and Xi index [F(1,103) = 5.43; P = 0.02; η2 = 0.05] reflects the inefficacy of OXTIN treatment alone to induce generosity in Xi high scorers (all P values > 0.75), whereas the peptide more than doubled the contributions of Xi low scorers to both the outgroup [t(34.52) = 2.40; P = 0.02; d = 0.68] and the ingroup [t(31.20) = 2.37; P = 0.02; d = 0.68; Fig. 1C].
Task design of Experiment 2. Given are corresponding examples of ingroup and outgroup case vignettes presented in Experiment 2. In total, the task consisted of 50 such vignettes briefly describing the personal needs of poor people, half of whom were framed as refugees (outgroup) and half of whom were framed as natives (ingroup), respectively.
To address the question of whether administration of a peer-derived altruistic norm in addition to OXTIN could augment altruistic responses in Xi high scorers, the task was reiterated in Experiment 3, with the exception that this time, each case presentation also included information about the average contribution choices of all their male and female peers enrolled in Experiment 1 (Fig. S2). A repeated-measures ANOVA with “norm” (present, absent) as an additional within-subject variable revealed a three-way interaction among treatment, Xi index, and norm [F(1,103) = 5.51; P = 0.02; η2 = 0.05]. Not surprisingly, deviation from the norm was relatively low for Xi low scorers due to their distinct altruistic tendency displayed in Experiment 2, which is consistent with a trend-to-significant effect of norm administration in PLCIN-treated subjects [outgroup, t(27) = 1.73 (P = 0.095; d = 0.34); ingroup, t(27) = 1.87 (P = 0.07; d = 0.35)] and no effect at all in OXTIN-treated subjects (all P values > 0.40). Intriguingly, application of OXTIN in conjunction with the altruistic norm prompted Xi high scorers, who had been resistant to either of these interventions alone (all P values > 0.64), to increase their outgroup-related donations by 74% [EUR 3.11 ± 3.37 with norm vs. EUR 1.79 ± 2.14 without norm; t(24) = 2.61; P = 0.02; d = 0.47; Fig. 1D]. This effect was weaker for the ingroup [EUR 2.46 ± 2.93 with vs. EUR 1.51 ± 2.00 without norm; t(24) = 1.81; P = 0.08; d = 0.38]. The facilitation of altruism observed in Xi high scorers becomes even more obvious when relativizing the donated sums to those obtained in Experiment 1; relative to this 100% benchmark, donations in Xi high scorers climbed from 23% to 38% as a consequence of pairing OXTIN treatment with the peer-derived altruistic norm.
Task design of Experiment 3. Given are corresponding examples of ingroup and outgroup case vignettes presented in Experiment 3. In contrast to Experiment 2, the vignettes contained normative incentives (i.e., participants were additionally informed about the average sums their peers had donated in Experiment 1 for each case).
