Is love for green in our genes? - Agnes van den Berg

ARTICLE IN PRESS2Y. Joye, A. van den Berg / Urban Forestry & Urban Greening xxx (2011) xxx–xxx“psycho-evolutionary framework” underlying SRT, RogerUlrich (1983) mainly explored the possible proximate causes ofrestoration induced by natural environments. These are theimmediate devel- opmental (ontogenetic) and mechanic causes ofa certain behaviour or trait. Based on the empirical work of RobertZajonc (1980), Ulrich (1983) argued that the initial response modeto environments and environmental stimuli is one ofgeneralized affect. Characteris- tic to such affective responses isthat they are deemed to occur almost immediately afterexposure to the stimulus or environ- ment, to require only littlecognitive processing, and to take place without consciousrecognition. This initial affective response mode is believed tohave prehistoric roots and to have been retained across thehuman lineage because it contributed to our species’ survival.Ulrich (1983, 1986) specified a number of specific environmentalfeatures or “preferenda” that are able to trigger initial positiveaffective responses. These include “complexity”, “gross structuralfeatures” (e.g., symmetries), “depth/spatiality cues”, “even groundsurface texture”, “deflected vista”, and “absence of threats”. Whatinterests us most, however, is that Ulrich (1983) also conjecturedthat exposure to unthreatening natural environments or to certaintypes of unthreatening natural content (e.g., vegetation) will offsetsuch immediate positive affective responses. When previousto encounters with such natural settings/elements an individualwas in a negative mood or experienced stress, then theposi- tive responses induced by nature could attenuate thosenegative feelings/states, and restoration might follow. Or, assummarized by Ulrich (1983, p. 116): “For individualsexperiencing stress or anxiety, most unthreatening naturalviews may be more arousal reducing and tend to elicit morepositively toned emotional reac- tions than the vast majority ofurban scenes, and hence are more restorative in apsychophysiological sense”.According to SRT, restorative responses can thus essentiallybe considered as by-products of immediate positive affectiveresponses induced by (unthreatening) natural settings. Note thatthe centrality of affect in SRT marks an important differencewith the other major theory on restorative environments, AttentionRestoration Theory (ART), which assumes that the proximatecause of restoration lies in the replenishment of depleted cognitiveresources (Kaplan and Kaplan, 1989). Of further importance is thatSRT assumes that the link between positive affect and restorativeresponses is specific to natural environments: “. . . modern humans,as a partly genetic remnant of evolution, have a biologically preparedcapacity for acquiring and retaining restorative responses tocertain natural settings and content . . . but have no such dispositionfor most built environments and their materials” (Ulrich, 1999,p. 52). But why would it have been beneficial for humans to evolvesuch a capacity? This question taps into the ultimate or evolutionarycauses of restorative responses to nature, which are the focusof this article.Ultimate explanations of restorative responses to natureDifferent ultimate explanations run through Ulrich’s psychoevolutionaryframework. For example, Ulrich notes that whena stressor has disappeared the incidence of stress reduction “...would enhance survival chances in part because of its role inpromoting recovery from fatigue and other deleterious effectsstemming from behaving adaptively in a previous demandingsituation” (Ulrich,1993, p. 98). It is indeed a well-known fact that after astress- ful episode a failure to return to baseline levels ofarousal may have detrimental health consequences and thusmay have low- ered survival chances (Selye, 1956). While thisaccount perhaps provides an ultimate explanation for theprevalence of a general stress reduction response, it must beclear that this is not the type of “restorative” response envisionedby SRT.The central idea underlying SRT is that human individuals morequickly and more deeply recover from stress near unthreateningnatural elements and settings than near unthreatening urban environments.As noted earlier, this particular restoration process issupposed to be driven by the differential affective valence of naturalversus urban settings. Since the 1980s there seems to be an(implicit) consensus among restorative environments researchersthat the occurrence of these affective responses is “.. affected byunlearned factors of evolutionary origin” (Ulrich, 1983, p. 115), andthat they need to be considered as remnants of our species’ evolutionin natural environments. Of further importance is that it ismostly assumed that these (positive) affective reactions are evolvedadaptations. Displaying such responses to nature fulfilled a particularfunction in ancestral environments and “. . . tended to foster[human] survival and well-being during evolution” (Ulrich et al.,1991, p. 209).It must be clear that the foregoing account still leaves a numberof questions unanswered. For example, in what respect did positiveaffective responses to unthreatening nature exactly foster survivalduring our species’ evolutionary history? Within the restorativeenvironments research field it is generally assumed that some naturalcontent could offer ancestral humans opportunities for safety,could contain food resources, or at least could have been indicativeof the presence of food or safety (cfr., Ulrich et al., 1991, p. 226).Having evolved a hardwired tendency or “preparedness” to displaypositive affective responses to such natural content would haveincreased ancestral humans’ survival chances because it motivatedthem to pay attention to, or to approach or stay in environmentsthat contained elements or opportunities that were critical to theirsubsistence (i.e., food and safety).Another issue relates to the type of nature toward which ourspecies is supposed to have evolved positive affective responses.Although the empirical and theoretical literature associated withSRT is not very often outspoken on this matter, three general categoriesof “restorative nature” can be identified. First, on numerousoccasions it is proposed that exposure to unthreatening naturalsettings can elicit these immediate positive affective responses.Ulrich (1993, p. 102), for example, notes that “[c]onsistent withthe functional-evolutionary perspective . . . viewing unthreateningnatural landscapes tends to promote faster and more completerestoration than . . . urban or built environments”. A second categoryof restorative nature is vegetative elements, or settingscontaining such elements. The reason for including this categoryderives from the fact that restorative effects are often triggered byvegetated scenes, a finding that is generally regarded to becon- sistent with, and supporting the evolutionary tenets of SRT(cfr., Ulrich et al., 1991). The third and last category of naturalcontent is more specific than the two previous ones, and includesspecific types of natural settings or features that are supposed tofacilitate stress reduction. Ulrich (2008, p. 90) points out that thesecan com- prise elements/features like “calm or slowly movingwater, verdant vegetation, flowers, savanna-like or parklikeproperties. . .”.Based on the previous discussion, SRT’s ultimate account forrestorative responses to nature can be summarized as follows.A biologically prepared readiness to display positive affectiveresponses to different types of unthreatening natural content isan evolved adaptive mechanism (Ulrich, 2008, p. 89), whose functionwas to guide and support our ancestors in the processof finding food, water and shelter in ancestral environments.When having experienced a stressful episode, exposure to naturalcontent providing food/water/shelter can lead to stress reductionvia the (psychologically and physiologically) soothing effects ofpositive affect (Ulrich, 2008). The fact that, on an evolutionarytime-scale, our species has only recently begun to construct andinhabit built environments, but has experienced the “.. rewardsassociated with natural settings during a few million years ofevolution” (Ulrich