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Hearth and Campfire Influences on Arterial Blood Pressure: Defraying the Costs of the Social Brain through Fireside Relaxation

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The importance of fire in human evolutionary history is widely acknowledged but the extent not fully explored. Fires involve flickering light, crackling sounds, warmth, and a distinctive smell. For early humans, fire likely extended the day, provided heat, helped with hunting, warded off predators and insects, illuminated dark places, and facilitated cooking. Campfires also may have provided social nexus and relaxation effects that could have enhanced prosocial behavior. According to this hypothesis, calmer, more tolerant people would have benefited in the social milieu via fireside interactions relative to individuals less susceptible to relaxation response. Using a randomized crossover design that disaggregated fire's sensory properties, pre-posttest blood pressure measures were compared among 226 adults across three studies with respect to viewing simulated muted-fire, fire-with-sound, and control conditions, in addition to tests for interactions with hypnotizability, absorption, and prosociality. Results indicated consistent blood pressure decreases in the fire-with-sound condition, particularly with a longer duration of stimulus, and enhancing effects of absorption and prosociality. Findings confirm that hearth and campfires induce relaxation as part of a multisensory, absorptive, and social experience. Enhancements to relaxation capacities in the human social brain likely took place via feedback involving these and other variables.
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Evolutionary Psychology
www.epjournal.net 2014. 12(5): 983-1003
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Original Article
Hearth and Campfire Influences on Arterial Blood Pressure: Defraying the
Costs of the Social Brain through Fireside Relaxation
Christopher Dana Lynn, Department of Anthropology, University of Alabama, Tuscaloosa, AL, USA. Email:
cdlynn@ua.edu (Corresponding author).
Abstract: The importance of fire in human evolutionary history is widely acknowledged
but the extent not fully explored. Fires involve flickering light, crackling sounds, warmth,
and a distinctive smell. For early humans, fire likely extended the day, provided heat,
helped with hunting, warded off predators and insects, illuminated dark places, and
facilitated cooking. Campfires also may have provided social nexus and relaxation effects
that could have enhanced prosocial behavior. According to this hypothesis, calmer, more
tolerant people would have benefited in the social milieu via fireside interactions relative to
individuals less susceptible to relaxation response. Using a randomized crossover design
that disaggregated fire’s sensory properties, pre-posttest blood pressure measures were
compared among 226 adults across three studies with respect to viewing simulated muted-
fire, fire-with-sound, and control conditions, in addition to tests for interactions with
hypnotizability, absorption, and prosociality. Results indicated consistent blood pressure
decreases in the fire-with-sound condition, particularly with a longer duration of stimulus,
and enhancing effects of absorption and prosociality. Findings confirm that hearth and
campfires induce relaxation as part of a multisensory, absorptive, and social experience.
Enhancements to relaxation capacities in the human social brain likely took place via
feedback involving these and other variables.
Keywords: absorption, blood pressure, fire, hypnotizability, prosociality, relaxation
response
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Introduction
Controlled fire has played a key role in human evolutionary history. For ancient
hominins, it would have provided the following: light to extend the day and illuminate
otherwise uninhabitable dark places; heat for cooking previously inedible food, warming
bodies at night, and enabling migration into colder climates; a weapon to facilitate mass
hunting and stave off predators; and, according to several scholars, social nexus. Wilson
(2012) argues that the habit of building campsites around fires reflects one of the hallmarks
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of eusocial speciesthe need to build and defend nests. Accessing, maintaining, and
benefitting from fire may have influenced cognition related to future-planning, response
inhibition, and group-level cooperation (Twomey, 2013); and such intensive use of fire,
especially for cooking, may have selected for hominins that were more tolerant of one
another (Wrangham, 2009). Likewise, McClenon (1997, 2002, 2006) speculates that Homo
erectus experiencing altered states of consciousness through the hypnotic influence of
watching campfires would have been more relaxed and prosocial than those that didn't.
This basis of his “ritual healing hypothesis” supposes that fire has the capacity to induce a
relaxation response, a position taken as given because of the common sentiment that hearth
and campfires are relaxing. Fires are multisensory experiences that have numerous
unexplored dimensions when considering human evolution. Through the current studies, I
investigate the basis of the ritual healing hypothesis by parsing the elements of fire and
examining their relationships to relaxation response, hypnotizability, absorption, and
prosociality.
Humans possess the ability to moderate relaxation response via conscious cognitive
processes, a capacity that has been attributed in part to fire manipulation, ritual behavior,
and the hypnotic influence of hearth and campfires during human evolution (McClenon,
1997, 2002, 2006; Rossano, 2007, 2010). Relaxation response, a wakeful hypometabolic
physiological state (Benson and Klipper, 2000) that deactivates or opposes stress response
(Stefano et al., 2003), is an evolutionarily old and highly conserved function that is part of
the negative feedback that deactivates stress response and has been directly linked to the
alleviation of stress-related disease (Esch, Fricchione, and Stefano, 2003; Esch, Stefano,
and Fricchione, 2002). Stress-related disorders are among the leading causes of disability in
the modern era and pose significant economic impacts worldwide (Kalia, 2002), so there is
great incentive to understand the evolved mechanisms and environmental triggers of stress-
reduction that are specific to humans.
As is true in contemporary populations, stress was doubtless both complexly
beneficial and maladaptive for hominin ancestors. Stress is a psychophysiological response
to uncontrollable or unpredictable changes in one’s environment (Koolhaas et al., 2011),
facilitating behavior to pursue rewardssuch as would have been required for coordinated
huntingand producing fight, flight, and freeze responses that help organisms avoid or
escape danger. As social group sizes increased, psychosocial factors also contributed
appreciable negative stress (Dunbar, 1993), given the calculus involved in mentally
simulating the potential number of social situations any individual could encounter
(Alexander, 1989; Flinn, Nepomnaschy, Muehlenbein, and Ponzi, 2011). Although
Sapolsky (1998) has shed much light on the stress dynamics of extremely social species,
human self- and other-awareness likely exacerbated this pressure in ways not well
understood (Flinn et al., 2011). Self- and other-awareness entail numerous benefitse.g.,
self-control, self-improvement, self-grooming, positive misperception, theory of mind, and
scenario-buildingbut they also accrue significant costs, such as self-isolation, analysis
paralysis, forecast inaccuracy, self-aggrandizement, resentment, egotism, envy, and guilt or
shame (Keenan, Gallup, and Falk, 2003). The rarity of such awareness within the animal
kingdom suggests these costs are significant. For self- and other-awareness to develop in
humans, these costs were likely mitigated, possibly by mechanisms associated with
partitioning awareness or psychological dissociation (Lynn, 2005).
The term dissociation is used for a family of experiences characterized by
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combinations of depersonalization, derealization, and absorption. These range from the
common and normal, such as “zoning out” while reading a book or playing a game, to the
rare and aberrant, as with dissociative disorders. Theoretical approaches tend toward either
a “psychiatric-adaptive” or an “anthropological-discursive” model (Seligman and
Kirmayer, 2008). The evolutionary approach underlying ritual healing theory holds that
dissociation is basically adaptive and functions to reduce or filter stress (Ludwig, 1983;
McClenon, 2006), but in cultural manifestations dissociation also has social and rhetorical
meanings (Seligman and Kirmayer, 2008). Although analogs appear in other species
(Schauer and Elbert, 2010), it is important to acknowledge that dissociation is not a unified
neural structure with a single essencethe varieties of dissociative phenomena simply
share the trait of featuring cognitive mechanisms that relinquish or direct information
processing away from the social self (Kirmayer, 1994). Dissociation is a feature of ritual
and non-ritual social behavior cross-culturally (Kirmayer, 1994; Seligman and Kirmayer,
2008), but it is difficult to discover when in evolutionary history this animal capacity was
enhanced. One possibility is that it developed in concert with language.
Several scholars suggest language, cooperation, and group size arose synergistically
and may have been pushed by the increased necessity of maintaining fires as humans
moved into geographic regions that suffered global cooling following the Mount Toba
eruption ~71,000 years ago (Ambrose, 1998; Burton, 2009; Gamble, Gowlett, and Dunbar,
2011; Gowlett, 2006, 2010; Rossano, 2007, 2010; Twomey, 2013; Wrangham, 2009). Fires
have been manipulated since roughly 1 million years ago (Berna et al., 2012), but there is
as yet no evidence of hominin knowledge of ignition or kindling until the Upper
Paleolithic, approximately the same period when evidence appears for elaboration of
symbolic communication (Gowlett, 2006, 2010; Twomey, 2013). This suggests that
ancestral groups migrated, were successful and grew in size, and then were pressured by
environmental change to better control fire as temperatures dropped. The inability to start
fires would have required groups to coordinate activities to access and maintain them. This
continual cooperation would have put pressure on cognitive capacities for social tolerance,
conceiving of others as collaborators in future cooperation, episodic memory to understand
past ecological problems, extended working memory of operations associated with fire
maintenance, and protolanguage to coordinate collective activities and intentions (Gowlett,
2006, 2010; Rossano, 2007, 2010; Twomey, 2013; Wrangham, 2009).
Campfires are still used as social pivots in modern societies, even when other forms
of light, warmth, cooking, and predator avoidance are available (see Figure 1). Fireplaces
are often kept in houses purely for decorative purposes, despite actually reducing heating
efficiency; TV channels and video recordings feature Yule fires that people watch; candle
flames are frequently used as visual foci for meditation; and virtual fires are marketed
under the auspices of promoting relaxation and used in therapeutic biofeedback (e.g., Riva
et al., 2010). Indeed, most other species avoid fire, save a few that use charcoal as medicine
or harvest other creatures serendipitously roasted in wildfires (Burton, 2009), a distinction
that seems to have had profound influences beginning approximately 400800 thousand
years ago (Twomey, 2013).
As hominin ancestors sat around hearth and campfires, they may have experienced
secondary relaxation benefits, particularly in the dark when other stimuli were limited and
firelight was the only thing to see well or focus on (McClenon, 1997). At night, circadian
rhythms and the properties of fire converge for hallucinatory effects, which may have
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influenced the emergence of religio-ritual behaviors (McClenon, 1997, 2002, 2006).
Konner (1985) reports that among the !Kung San foragers of the Kalahari Desert, there was
likely a synergy between the music, dancing, hyperventilation, smoke inhalation, and
staring into flames that produced an effect unlike any other. A parlor trick at the heart of
the children’s game Bloody Mary affirms the visual distortions firelight can create in the
dark (Caputo, 2010). Additionally, close proximity fire could have benefited social
behavior through the influences of blue spectrum light on mood and other cognitive
processes (Burton, 2009).
Figure 1. Humans build nests around fires and enjoy the mesmeric effects when camping,
even though more efficient resources are available
Photo courtesy of Heath Kinzer
The model I have outlined for a cognitive evolutionary influence of fire via its
relaxation effects is based in part on the common sentiment that firelight is relaxing and
that relaxed people are more amiable, but neither this supposed absorptive-hypnotic
influence nor a link to prosociality have been empirically verified. Therefore, through the
project outlined in this article, I tested the hypothesis that the properties of hearth and
campfires influence relaxation by reducing blood pressure and that this reduction is
enhanced by hypnotizability, absorption, and prosociality. Because fire is a multisensory
and often social experience and it would otherwise be difficult to assess what was
influencing blood pressure, I used experimental conditions to parse sensory and social
elements and test the following predictions:
1. Watching a fire should result in lower blood pressure than a control condition.
2. An audiovisual fire experience should result in lower blood pressure than a control
condition.
3. An audiovisual fire experience should result in lower blood pressure than merely
watching a fire with no sound component.
4. Hypnotizability, absorption, and prosociality should interact with the fire stimulus
to increase relaxation response.
This project changed over time because of feedback from participants and
preliminary analyses, and I therefore present it as three studies conducted in conjunction
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with a number of undergraduate research assistants. Protocols for all three studies as
outlined below were approved by the University of Alabama Institutional Review Board.
Study 1
Materials and Methods
Data were collected by undergraduate assistants, who recruited 64 adults (51
women), ages 1936 (M ± SD = 21.8 ± 3.84), via University of Alabama courses and
community postings from September 2010May 2011 to complete study questionnaires
and measurements. After obtaining contact information from potential participants, an
email was sent explaining the study and what it entailed. Participants were scheduled to
come to our lab and complete study protocols. I excluded one person who reported taking
medication known to control blood pressure, leaving a total of 63 participants for analysis.
Upon arrival, participants provided informed consent, completed a questionnaire,
and were assessed for hypnotizability, which took approximately 10 minutes, allowing their
heart rates to return to steady-state before the first blood pressure measure. The survey
queried sex; age; ethnicity; occupation; education level; major, grade point average, and
credit hours (if student); social status (Singh-Manoux, Adler, and Marmot, 2003);
relationship status; medication; social support (Blake and McKay, 1986); perceived stress
(Cohen and Williamson, 1988); and religiosity (Rohrbaugh and Jessor, 1975).
Hypnotizability was assessed using the eye-roll test (Spiegel, 1972), which entails
rotating one’s eyes toward the top of the head while keeping the head still, then slowly
rolling one’s eyelids down while continuing to look up (see Figure 2). The amount of sclera
visible during the upgaze and roll (or squint if they cannot roll) is assessed on a 5-point
scale (or 4-point scale for squints if they cannot roll their eyes down; 0 = least sclera
visible/least hypnotizable). A team of trained raters conducted scoring to achieve
agreement. Despite a 75% success rate in predicting hypnotizability in clinical cases, the
validity of the eye-roll test relative to other hypnotizability measures is only 0.22 (Hilgard,
1981, 1982), but it has the benefit of providing a spot assessment not possible via other
methods.
Figure 2. Upgaze (a and b) and eye roll (c and d) variations associated with hypnotic
capacity
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Blood pressures were assessed with regard to a 5-minute fire simulation on a
computer screen as the experimental condition and a 5-minute blank computer screen as the
control condition. Blood pressure was measured in millimeters of mercury (mmHG) before
and after each condition using an Omron HEM-711 automatic blood pressure monitor
(Omron Healthcare, Inc., Bannockburn, IL), which has reliability equivalent to mercury
sphygmomanometers (Rotch, Dean, Kendrach, Wright, and Woolley, 2001). The fire
condition involved watching a randomly assigned digital recording of either a hearth or
campfire (Ambient Fire, Jumby Bay Studies, 2006) with the sound muted (see Figure 3). In
the control condition, participants merely watched a blank computer screen (i.e., powered
off). Conditions were administered on a 19” computer monitor while wearing noise-
cancelling headphones in a darkened office with the doors closed and noise kept to a
minimum, though an experimenter remained in or just outside the room to monitor the
session. The headphones limited exposure to distractions outside the room so participants
could focus more easily in both conditions. The darkened room was meant to simulate
nighttime fireplace or campfire environments, when outside lights would be dimmed or
absent. Participants sat with their faces approximately 30–40” from the screen in a
cushioned desk chair with armrests, rollers, and a straight back. They were asked to turn off
their cell phones and other devices and not do anything else while watching the screen,
though they could move slightly or make adjustments if need be. Participants were
randomly assigned to either the control or muted-fire first and completed both conditions.
Room temperature was monitored continually throughout both conditions (M ± SD =
74.8°F ± 3.70, min/max = 67.5/83.6) and controlled for in preliminary analyses, but made
no statistical difference.
Figure 3. Screenshots of hearth and campfire videos used in fire conditions
I analyzed the data using SPSS version 20 for Windows (IBM Corp., Armonk, NY).
I calculated descriptive statistics for demographic and dependent variables and, following
the recommendation of Simmons, Nelson, and Simonsohn (2011), have provided statistics
of only those measures used for analyses. To test the hypothesis that the muted-fire
condition would influence blood pressure reduction relative to the control condition, I
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compared mean systolic and diastolic blood pressure (pre- and posttest) using paired
samples t-tests and considered results significant at p < .05.
Results
There were significantly more women than men in the sample, and the mean age
was relatively low, reflecting a preponderance of college-age participants. These subjects
were ethnically representative of the community, with 89% self-reporting as white, 9% as
African-American, 2% as Hispanic, and 2% not answering. Seventy-eight percent were
college students and 44% were single, with the remainder in some type of relationship.
Subjects were predominantly upper-middle status (M ± SD = 6.7 ± 1.34), according to self-
report on a 10-point scale (1 = least money/education, worst job, and fewest friends) and
average in hypnotizability (M ± SD = 2.6 ± 1.03).
Fifty-seven percent of participants received the fire condition first. Mean systolic
blood pressure across all three measures was 115.7 mmHG, and mean diastolic pressure
was 75.0. Comparison of the blood pressure of women (systolic: M ± SD = 117.2 ± 9.75;
diastolic: M ± SD = 75.6 ± 9.65) and men (systolic: M ± SD = 127.0 ± 12.25; diastolic: M ±
SD = 75.6 ± 12.92) at the first measure indicated a significant difference in systolic
pressure, t(62) = -3.0, p = .004, but not diastolic pressure, t(62) = 0.01, p = .99.
In testing the hypothesis, as Figure 4 illustrates, there was a significant decrease in
systolic blood pressure in the muted-fire condition (M ± SD = 3.21 ± 9.35), t(62) = 2.72, p
= .01, and a non-significant decrease in diastolic pressure (M ± SD = 2.05 ± 10.51), t(62) =
1.55, p = .13. In the control condition, a systolic decrease was borderline significant (M ±
SD = 2.10 ± 8.50), t(62) = 1.96, p = .06, and diastolic pressure increased slightly from pre-
to posttest (M ± SD = -0.89 ± 7.69), t(62) = -0.92, p = .36. Randomization of hearth or
campfire had no effect.
Figure 4. Study 1 comparisons of mean blood pressure with paired samples t-tests indicate
a significant pre-post decrease for systolic pressure in the muted-fire condition
Note. p-values shown above bars; Error bars represent 95% CI
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Discussion
The prediction that fire is captivating because of its visual flickering, influencing a
relaxation response, was partially supported by reductions in blood pressure in the muted-
fire condition, especially compared to the increase in diastolic pressure in the control.
However, the short durations and anecdotal reports by participants that both conditions
were unrealistic though somewhat relaxing indicated the need for modifications.
Study 2
Materials and Methods
Study 2 was conducted from September 2011May 2012. One hundred nine
additional participants were recruited in the same manner as Study 1 and tested with regard
to 5-minute muted-fire, fire-with-sound, and blank computer screen conditions. Of these
additional subjects, six were excluded because blood pressure measures were incomplete.
The combined total sample of data from Study 1 and Study 2 participants retained for
analysis came from 121 women and 46 men, ages 1953 (M ± SD = 21.5 ± 4.3).
The hearth- and campfire-with-sound condition included naturalistic crackling
noises and, for the campfire, faint nature ambience delivered through the headphones,
which provided a more natural simulation. Because populations and protocols for Study 1
and Study 2 were the same except for the addition of a new condition, samples were
combined for hypothesis testing. I assessed blood pressure changes and the influence of
hypnotizability using repeated measures analyses of variance (ANOVA), controlling for the
sex disparity in the sample, established age-related variation in blood pressure (Franklin et
al., 1997), and trial sequence. To assess differences between group combinations, I used
post-hoc pairwise comparisons with Bonferroni adjustments (by multiplying the p-value by
the number of comparisons). All other protocols and analyses were the same as those in
Study 1.
Results
As with Study 1, the majority of participants were white (80%), upper-middle status
(M ± SD = 6.4 ± 1.22) college students (97%), with minorities of African-American (4%),
Hispanic (5%), and Asian (1%), with the remainder (11%) not answering; and they were
average in hypnotizability (M ± SD = 2.94 ± 0.87).
Among Study 2 participants, 33% received the fire-with-sound condition first, 37%
received it as their second trial, and 30% received it last. Mean systolic blood pressure was
116.1 ± 10.63 (women: M ± SD = 112.7 ± 8.64; men: M ± SD = 125.2 ± 10.06; t[101] =
-8.0, p < .01), and diastolic was 73.7 ± 8.29 (women: M ± SD = 73.2 ± 8.03; men: M ± SD
= 75.1 ± 8.88; t[101] = -1.3, p = 0.19).
Differences among conditions in the combined sample of Study 1 and Study 2
participants are depicted in Figure 5 and indicate a significantly greater difference in
systolic blood pressure (M ± SD = 3.52 ± 7.67; t[101] = 4.63, p = .001) and diastolic blood
pressure (M ± SD = 2.31 ± 10.69; t[101] = 2.19, p = .03) in the fire-with-sound condition
relative to muted-fire (systolic: M ± SD = 1.48 ± 8.79; t[165] = 2.17, p = .03; diastolic: M ±
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SD = 0.45 ± 9.74; t[165] = 0.59, p = .56) or control (systolic: M ± SD = 2.02 ± 8.03; t[165]
= 3.25, p = 001; diastolic: M ± SD = 0.05 ± 7.06; t[165] = 0.10, p = .92). However, Figure 5
also shows that the pretest blood pressure in the fire-with-sound condition was significantly
elevated relative to the control (systolic: t[102] = 2.42, p = 0.02; diastolic: t[102] = 2.12, p
= .04) and muted-fire (systolic: t[102] = 2.49, p = .01; diastolic: t[102] = 2.56, p = .01),
despite trial randomization.
Figure 5. Comparisons of mean blood pressure with paired samples t-tests of combined
Study 1 and Study 2 participants indicated significant pre-post decreases in all conditions
for systolic pressure and only in the sound condition for diastolic pressure
Note. p-values shown above bars; Error bars represent 95% CI
One-way repeated measures ANOVAs were used to test for differences among
groups and indicated a borderline significant influence of the condition, with a moderate
effect size for systolic blood pressure, F(2, 100) = 2.90, p = .06, partial eta2 = 0.055. Post-
hoc pairwise comparisons with Bonferroni adjustments indicated a borderline significant
difference between muted and sound conditions (p = .06). However, two-way repeated
measures ANOVA models including hypnotizability as a between-subject factor, condition-
by-hypnotizability as a within-subjects factor, and controlling for sex, age, and trial
sequence (see Table 1) were not significant and indicated the between-subjects effect for
systolic blood pressure was largely due to age, F(1, 54) = 3.20, p = .08, partial eta2 = 0.054.
There were no significant differences in diastolic measures and no significant interactions
with hypnotizability or pairwise differences for systolic or diastolic pressure.
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Table 1. Two-way repeated measures ANOVA for systolic and diastolic blood pressures
with sex, age, and trial sequence as covariates
F
df
p
Partial eta2
Systolic Blood Pressure
Condition
1.7
2, 168
.18
0.020
Condition-x-hypnotizability
0.8
8, 168
.59
0.009
Hypnotizability
1.0
4, 84
.41
0.046
Diastolic Blood Pressure
Condition
0.6
2, 112
.57
0.010
Condition-x-hypnotizability
0.5
8, 112
.86
0.034
Hypnotizability
0.7
4, 56
.63
0.044
Discussion
In study 2, I tested the revised hypothesis that fire with sound would produce the
greatest relaxation effect and muted fire would be secondary in its influence, controlling for
baseline variation in hypnotizability. I found a reduction from pre- to posttest in the fire-
with-sound condition that approached significance, but only with regard to systolic blood
pressure; it is possible this effect was due to the relatively elevated blood pressure in the
fire-with-sound pretest. Muted fire did not produce the effect I expected and, based again
on post-experiment reports from participants, may have been an irritant because of its lack
of other sensory components. Furthermore, the greater influence on systolic pressure
according to the two-way ANOVA appears to have been age.
As with Study 1, participants reported that the period of time for each condition was
so short the entire experiment felt like a relaxing respite from other obligations, indicating
the need to extend trial durations in subsequent study.
Study 3
Materials and Methods
Ninety-five adults were recruited from September 2013May 2014 for Study 3 via
the same mechanisms as studies 1 and 2 but were sent a link to complete questionnaires
online before being scheduled for the experimental conditions. Twenty-three did not arrive
for the experimental portion, and another 11 did not provide enough information for
inclusion, leaving 60 participants (53 women) for Study 3 analyses.
Feedback regarding Study 2 led to several modifications in Study 3. An expanded
survey queried the following: experience with fireplaces and campfires, computers,
television, and smartphones (to control for conditioning to fire- and screen-based
relaxation); anxiety (to control for ability to relax during the experiment); absorption (as a
better validated measure than the eye-roll test of ability to focus attention); and prosociality
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(to test fire’s theorized role in influencing cooperation and social tolerance). Caffeine,
tobacco, and recreational drug use were queried as possible influences on blood pressure or
relaxation but exhibited no associations. Participants were also asked to complete a paper-
and-pencil exit-survey upon finishing the experiment.
Absorption was measured using the Tellegen Absorption Scale (TASTellegen
and Atkinson, 1974) on a 5-point Likert array (Glisky, Tataryn, Tobias, Kihlstrom, and
McConkey, 1991). TAS is a 34-item standardized survey and elicited a reliability
coefficient of 0.92 for this study. Anxiety was measured using the State-Trait Anxiety
Inventory (Spielberger and Gorsuch, 1983), which is a standardized survey including two
20-item subscales that measure anxiety with regard to one’s current state and the degree to
which it is part of one’s general personality. Cronbach’s alphas for state and trait anxiety
were both 0.91, indicating excellent reliability, but state anxiety had a significantly lower
response rate and was therefore excluded from analyses. Media and fire habituation were
elicited with items querying the average number of leisure hours per week spent in front of
a TV, computer, or smartphone (1 = none, 2 = 12, 3 = 35, 4 = 59, 5 = 10+),
and no/yes questions measured if one’s family home had a fireplace that was regularly
used, if the participant had gone camping often and built fires, or if the TV was the center
of the family home. I tested these items for collinearity and, finding none, summed them to
create a single variable. Prosociality was measured using 43 items from the Myer-Briggs
Personality Inventory (Myers and McCaulley, 1988) and the Altruistic Personality Scale
(Rushton, Chrisjohn, and Fekken, 1981). These combined items achieved an extremely
reliable Cronbach’s alpha of 0.85.
Because Study 1 and Study 2 participants indicated that all 5-minute conditions
were relatively relaxing, condition lengths were extended to 15 minutes. Additionally, the
blank computer screen control was replaced with an upside-down screenshot of the
campfire used in the other conditions (see Figure 6). Given the hypothesis that the
flickering light and sudden sounds may stimulate orienting response, the upside-down
static fire retains the structural properties of the experimental fires (e.g., color, brightness,
shapes) while eliminating and thus isolating other sensory aspects that may be effective. All
other Study 3 protocols were the same as those in studies 1 and 2.
I conducted analyses using repeated measures ANOVAs as in Study 2.
Figure 6. Upside-down static campfire image used in study 3 to control for structural
features of a normal fire
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Results
As in studies 1 and 2, subjects were mostly white (69%), upper-middle status (M ±
SD = 6.4 ± 1.53) college students (76%) with average hypnotic capacity (M ± SD = 2.9 ±
0.66), and were also average in absorption (M ± SD = 71.0 ± 14.95).
Thirty-eight percent of the participants received the fire-with-sound condition first,
35% received it second, and 27% received it third. Mean systolic blood pressure at the first
measure was 124.4 ± 7.91 (women: M ± SD = 114.8 ± 9.95; men: M ± SD = 134.0 ± 5.86;
t[58] = -4.98, p < .001), and diastolic pressure was 72.6 ± 7.93 (women: M ± SD = 72.8 ±
8.11; men: M ± SD = 72.4 ± 7.74; t[58] = 0.11, p = .91). Average change in blood pressure
is depicted in Figure 7 and shows that blood pressure increased in the control (systolic: M ±
SD = -3.2 ± 7.06; diastolic: M ± SD = -2.4 ± 8.48) and muted-fire (systolic: M ± SD = -3.3
± 7.06; diastolic: M ± SD = -2.0 ± 9.43) conditions but decreased in the fire-with-sound
condition (systolic: M ± SD = 5.9 ± 7.36, diastolic: M ± SD = 3.0 ± 7.53). However, the
pretest blood pressure was significantly elevated in the fire-with-sound condition relative to
the control (systolic: t[69] = 6.97, p < .001; diastolic: t[69] = 3.69, p < .001) or muted-fire
(systolic: t[69] = 6.97; p < .001; diastolic: t[69] = 3.64; p = 0.001), despite randomization
of the order of the conditions. Furthermore, posttest blood pressures were lower in the fire-
with-sound condition than for the control (systolic: t[66] = -1.32, p = .19; diastolic: t[66] =
-1.85, p = .07) and muted conditions (systolic: t[66] = -1.32, p = .19; diastolic: t[66] =
-1.85, p = .07). Though these latter differences were not statistically significant, they
indicate a relatively large decrease overall in blood pressure for fire-with-sound.
Figure 7. Study 3 comparisons of mean blood pressure with paired samples t-tests
indicated significant pre-post increases in systolic and diastolic in the control condition and
in systolic in the muted condition but significant pre-post decreases in systolic and diastolic
in the sound condition
Note. p-values shown above bars; Error bars represent 95% CI
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A one-way repeated measures ANOVA indicated a significant influence of
condition for systolic pressure with a large effect size, F(1, 66) = 45.04, p < .001, partial
eta2 = 0.406. Post-hoc pairwise comparisons indicated significant differences between fire-
with-sound and control (p < .01) and between fire-with-sound and muted-fire (p < .01). I
also found a significant difference with a large effect size for diastolic pressure, F(2, 65) =
7.40, p = .001, partial eta2 = 0.185, with significant pairwise differences between fire-with-
sound and control (p = .001) and between fire-with-sound and muted-fire (p = .01).
I tested the influence of hypnotizability, absorption, and prosociality on these
differences using two-way ANOVA models while controlling for sex, age, anxiety,
screen/fire habituation, and trial sequence. As outlined in Table 2, the systolic multivariate
model was borderline significant with a large effect size and a borderline significant
within-subjects condition-by-prosociality interaction. Pairwise differences between fire-
with-sound and control and fire-with-sound and muted-fire remained significant (p = .03).
The diastolic multivariate model for condition and pairwise comparisons were not
significant, but there was a significant within-subject condition-by-absorption interaction
and a large between-subject effects for absorption and prosociality (see Table 2).
Table 2. Two-way repeated-measures ANOVAs for systolic and diastolic blood pressure
with sex, age, anxiety, screen/fire habituation, and trial sequence as covariates
To understand the nature of these effects, I transformed absorption and prosociality
into dichotomous variables based on their means (absorption: low = 4271, high = 72101;
F
df
p
Partial eta2
Systolic Blood Pressure
Within-subjects
Condition
3.2
2,62
.05
0.092
Condition-x-hypnotizability
1.3
4,62
.28
0.077
Condition-x-absorption
0.4
2,62
.71
0.011
Condition-x-prosociality
3.1
2,62
.05
0.091
Between-subjects
Hypnotizability
0.8
3,31
.48
0.047
Absorption
0.3
1,31
.59
0.010
Prosociality
3.0
1,31
.10
0.087
Diastolic Blood Pressure
Within-subjects
Condition
1.0
2,42
.40
0.043
Condition-x-hypnotizability
0.2
4,62
.93
0.013
Condition-x-absorption
4.1
2,62
.02
0.116
Condition-x-prosociality
1.9
2,62
.17
0.057
Between-subjects
Hypnotizability
0.7
2,31
.51
0.042
Absorption
12.4
1,31
.001
0.285
Prosociality
8.3
1,31
.01
0.212
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Evolutionary Psychology ISSN 1474-7049 Volume 12(5). 2014. -996-
prosociality: low = 67101, high = 102135) so they could be plotted against pre-posttest
blood pressure differences at each condition. Figures 8a and c suggest that those relatively
higher in absorption were more relaxed in the control and muted-fire trials than participants
with lower absorption, but the fire-with-sound condition not only produced the greatest
relaxation effect, it did so amongst those with the lower absorptive capacities. Figures 8b
and 8d illustrate a similar relationship with regard to prosociality, except that the relaxation
effect is diminished in the fire-with-sound condition for those more highly prosocial.
Figure 8. Between-subjects effects of absorption (a and b) and prosociality (c and d)
dichotomized as high/low and plotted against estimated marginal means of pre-posttest
differences in systolic (a and c) and diastolic (b and d) blood pressure across conditions,
controlling for sex, age, anxiety, screen/fire habituation, and trial sequence
Finally, 51% of Study 3 participants provided study feedback via the post-
experiment survey. Thirty-eight percent of those respondents found the fire-with-sound
condition the most relaxing, while 11% felt it was the muted-fire condition, and 1%
preferred the control.
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Discussion
In Study 3, I found a significant decrease in blood pressure in the fire-with-sound
condition and effects of absorption and prosociality. Although these effects were not
consistent across models, they support the hypothesis that the fire-with-sound condition is
the most influential in effecting relaxation response and involves focused attention and
cooperative intent. The hypothesis that muted fire would be secondarily influential,
however, was not supported.
By extending the duration of conditions and using a finer-grained control, Study 3
established the influential effect of fire-with-sound versus the other conditions as a
multisensory experience rather than a visual effect. In fact, the upside-down image had
unforeseen side effects, as several participants reported seeing faces in the image or that the
inversion bothered them.
Despite validating Study 2’s t-test and one-way ANOVA results, Study 3 also
replicated a curious elevation in the pretest blood pressure for the fire-with-sound
condition, which cannot be accounted for by trial sequence. Continued research should
compare fire with sound to more naturalistic conditions to explore the physiological
influences fireside environmental and circumstantial factors exert on relaxation response.
General Discussion
Across three studies, I tested the common belief that staring into fires is relaxing, a
rather noncontroversial supposition but one that lacked empirical support or explanations as
to why fires might elicit said effect. I used a randomized, controlled pre-posttest paradigm
that measured arterial blood pressure to investigate the model that fire’s relaxing influence
comes via hypnotic susceptibility (McClenon, 1997, 2002, 2006). Specifically, I
hypothesized that just watching a fire without any other sensory stimuli would produce a
hypnotic quiescence that would lower blood pressure relative to control conditions. In
testing this with two different controls across three different studies, I found little support
for a visual-only effect. My next hypothesis was that a combined audiovisual experience of
fire would result in lower blood pressure than control conditions, which was supported in
studies 2 and 3 through t-tests and when controlling for covariates in regression models. A
third hypothesis was that the visual fire with sound would be more effective in producing
relaxation than the fire without sound, which also was supported in studies 2 and 3. Finally,
I predicted that hypnotizability, absorption, and prosociality would interact with the fire
stimuli to increase relaxation response and, indeed, found absorption and prosociality
predict the greatest degree of relaxation, particularly in the fire-with-sound condition.
Several overall conclusions can be drawn from these findings. First, it appears that
fire with sound consistently produces reductions in systolic and diastolic blood pressure,
and reductions grow stronger with temporal exposure. Second, muted fire produces an
inconsistent effect, resulting in decreases in blood pressures in studies 1 and 2 but not much
moreand sometimes lessthan control conditions. It appears that initial relaxation in the
muted-fire condition may get counteracted as participants grow bored or annoyed. Finally,
there does not appear to be a steady linear increase in relaxation effect in moving from a
blank screen as control (no visual pattern, no movement, no sound) to a static image (visual
pattern, no movement, no sound) to muted fire (visual pattern, movement, no sound) to
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auditory fire (visual pattern, movement, sound). Instead, it seems that a blank screen leads
to modest relaxation, a static image has no relaxation effect, muted fire has variable effects,
and fire with sound is consistently relaxing and increasingly so with greater exposure.
The blank screen appears to allow viewers to focus their attention and use their
imaginations for relaxation, whereas the static image seems confusing and meaningless,
leading to cognitive dissonance. Muted fire seems to allow for the visual focusing of
attention, but the lack of sound may be distracting, leading viewers to listen for external
sounds or get caught up in their own thinking and planning, since the experiments took
place during the day in the midst of classes. This distraction effect likely increased with
time, resulting in the increased pre-posttest blood pressures of Study 3. Fire with sound is
visually and aurally naturalistic, allowing for multisensory absorption into the experience,
and thereby provided the greatest relaxation effect. This was supported by the significant
associations with absorption in Study 3 and greater relaxation for people higher in
absorption, particularly in the fire-with-sound condition. Nevertheless, pre-posttest
reduction in systolic pressure was observed across all three studies.
Greater variability in systolic than diastolic pressure is consistent with blood
pressure research (Littler, West, Honour, and Sleight, 1978; Watson, Stallard, Flinn, and
Littler, 1980), supporting the general hypothesis that sitting in front of a fire benefits
relaxation response, but such fireside relaxation may be enhanced in social settings.
Subjects were largely alone in this study, but those scoring higher in prosociality received
greater relaxation benefits, supporting Wrangham’s (2009) suggestion that manning fires
may be functionally related to social gregariousness. Future research should consider
fireside relaxation effects under varying social circumstances.
Stress reduction in the fire-with-sound condition also lends credence to the theory
that fireside healing rituals could have benefited dissociative genotypes (McClenon, 1997,
2002, 2006). Although still speculative, understanding the relaxing influences of fire could
be critical to unraveling mysteries of human cognitive evolution. For instance, selection to
suppress prepotent selfish impulses in favor of cooperative planning and maintenance of
fires (Rossano, 2007, 2010; Twomey, 2013) could have been abetted by relaxation effects
(Hudetz, Hudetz, and Reddy, 2004). Susceptibility to relaxation appears to vary by
circadian phase (Gorman and Lee, 2002) and, therefore, could be affected by time of day
and fire-influenced phase shifts. Future tests can address this by controlling for time and
varying the intensity of blue light (Vandewalle et al., 2007, 2010) and lux entering the eye
(Burton, 2009).
Furthermore, given the theoretical role of fireside relaxation in enhancing
dissociative phenotypes (McClenon, 1997, 2002) and associations among hypnotizability,
absorption, and anomalous experience (Cardeña and Terhune, 2008), I expected to see an
interaction between the experimental condition and hypnotizability and absorption, which
are both aspects of or closely related to dissociation (e.g., Granqvist, Reijman, and
Cardeña, 2011; Luhrmann, 2005; Snodgrass, Lacy, Dengah, Fagan, and Most, 2011;
Winkelman, 2011). Consistent with Glisky et al. (1991), hypnotizability and absorption
were positively associated in this study, but a significant effect was observed only with
regard to absorption. Yet hypnotizability and absorption differ in that the former is more
associated with suggestibility and the latter subject to conditioning (Zachariae, Jorgensen,
and Bjerring, 2000; Zachariae et al., 2007). People high in absorption may be more
sensitive to minute psychological and physiological changes associated with autonomic
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nervous system activity (Zachariae et al., 2000), which may lead them to be more prosocial,
whereas absorption has been associated with “personal mental thin boundaries, but not to
‘world’ boundaries such as opinion of others” (Cardeña and Terhune, 2008; p. 61). My
findings in this regard are inconclusive because of the low reliability of the eye-roll
technique, but the significance of this line of inquiry is that hypnosis and hypnotic guided
imagery therapy have been associated with psychoneuroimmunological benefits
(Zachariae, 2009). More reliable methodology might confirm similar autonomic effects for
firelight.
Several caveats should be borne in mind when considering these interpretations.
The sound of fire may be more influential than the visual component, so future efforts
should test sound-only conditions. The significantly elevated blood pressure for the fire-
with-sound pretest condition in studies 2 and 3 is a concern. This anomaly cannot be
explained by trial sequence or experiment priming, since conditions were randomized and
posttest measures of the preceding condition were pretest measures of the following, but it
should be investigated. Also, despite controlling for factors that would influence relaxation
response, a fire on a computer screen presents a number of obvious limitations, not the least
of which are the lack of fire’s warmth and smell and the awkwardness of sitting alone or in
a room with an experimenter, knowing that one is under surveillance. In the future, the
influences of heat, smell, and social context will have to be tested to minimize these
impediments. The social effect of sitting around a fire and conversing is doubtless very
important in fireside relaxation and the evolution of cooperation.
Conclusion
Hearth and campfires are widely held to influence a relaxation effect. Although the
importance of controlled fires in human evolution is indisputable, the relaxation aspect had
remained uninvestigated. In the course of three studies with varying sensory conditions, I
found significant reductions in blood pressure associated with fire with a naturalistic
auditory component, confirming commonly perceived relaxation effects of hearth and
campfires. However, lack of significant relaxation effects when subjects watch a flickering
fire but are deprived of its sound indicate the influence of fire is not a visual “trance-
inducing” effect alone. Furthermore, the combined audiovisual relaxation effect of fire is
enhanced among those with greater capacities for absorption and prosociality. These
findings complement models of human cognitive evolution with regard to fire control and
use and warrant further research to assess more fine-grained psychophysiological
influences, as well as evolutionary and therapeutic implications, especially with regard to
the communal influences of fires at group levels.
Acknowledgements: Preliminary data from this study have been presented at meetings of
the Society for Psychological Anthropology, the American Anthropological Association,
the Southern Anthropology Society, the NorthEastern Evolutionary Psychology Society,
the UA EvoS Club, and the Society for Anthropological Sciences. Thank you to all
members of the University of Alabama Human Behavioral Ecology Research Group for
assistance in conducting this study and to Jim Bindon, Bill Dressler, Larry Schell, Nate
Pipitone, Gordon Gallup, Matt Rossano, Michaela Howell, Elizabeth Rowe, Megan
Workman, three anonymous reviewers, and editor Elizabeth Cashdan for helpful comments
Hearth and campfire influences on blood pressure
Evolutionary Psychology ISSN 1474-7049 Volume 12(5). 2014. -1000-
on previous drafts. The author has no competing interests in interpreting or presenting these
data.
Received 04 June 2013; First Revision Submitted 02 June 2014; Second Revision
Submitted 01 August, 204; Accepted 13 September 2014
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... We may be drawn to the warmth it produces, watching the ickering ames, or listening to the sounds of the crackling wood-whichever it is, the multisensory components of re captivate humans in a unique way. In one previous study, a simulated re on a DVD in uenced a relaxation response even during the daytime in a laboratory setting (Lynn, 2014). In the current study, we tested the in uence of an electric replace speci cally designed for meditative effects. ...
... We retested the widespread belief that staring into res is relaxing using an electric replace instead of the DVD re used in the original study (Lynn, 2014). In this replication study, we expected cardiovascular activity to decrease the most with the audiovisual experience of the electric replace. ...
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In previous research, fire’s sensory components were disaggregated into separate experimental conditions using a Yule log video to test the hypothesis that domestic fire can induce a relaxation response. The study recorded blood pressure and skin conductance before and after participants watched the 15-minute fire video with and without sound and found a relaxation effect for the audiovisual condition. The current study replicates this with an electric fireplace by measuring pre- and posttest blood pressure (and calculated mean arterial pressure [MAP]) and heart rate (HR) using a randomized crossover design with 101 adults aged 18–60. We duplicated the three original experimental conditions and added an additional condition of fire sounds only. We predicted that the multisensory condition would produce the most relaxation and among those highest in absorption and prosociality. We found a relaxation response for all conditions and more consistent relaxation (systolic, MAP, and HR) and an absorption effect for the multisensory effect; however, the absorption effect was the opposite of our prediction (pre-trial MAP = 92.19 ± 10.95; post-trial = 90.61 ± 10.05, P = .02, df = 97). Our data partially replicate the original study, but the roles of absorption and prosociality need further exploration.
... They are storytellers (Cree & Gersie, 2014) and use a range of creative skills and practices to support participants' engagement (Harding, 2021). This includes offering opportunities for participants to undertake creative endeavour, like creating wild art and bush craft (Coates & Pimlott-Wilson, 2019;Harris, 2018), role play and drama (Craft et al., 2014), campfire cooking (Lynn, 2014) and singing/music (Brady, 2011;Ward, 2018). Through this, Forest School offers opportunities for creative and spiritual growth (Knight, 2017), allowing participants to connect with their inner selves through a connection with the wilder world. ...
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A growing evidence base has demonstrated the value of Forest School as an outdoor learning approach which supports a range of benefits including improved physical, social and mental wellbeing, increased confidence and self‐esteem and the development of problem‐solving skills. However, critics of Forest School have argued that a lack of theoretical coherence and detail risks the misinterpretation of Forest School and its pedagogy by both practitioners and researchers. This paper responds to these concerns, establishing a comprehensive and detailed theoretical framework for Forest School. Through a thorough examination of evidence supporting Forest School delivery, we examine the theoretical keystones of this pedagogical approach to inform an interdisciplinary theoretical understanding of Forest School. We argue that Forest School is a particular socially constructed approach to outdoor education, which is informed by social constructivist experiential learning theory. This is driven by two core components. First, play‐pedagogy, which includes the opportunity to experience risk and be creative. Next, biophilic interaction, which examines the human innate desire to be in nature. This is informed by the cultural origins of Forest School development as underpinned by Nordic notions of friluftsliv and by theories of place attachment. Taken together, this theoretical framework considers the breadth of knowledge that underpins Forest School and recognises its growing evidence base, which positions it as a rich and valuable pedagogical approach.
... Plants fueled the early anthropic controls of fire since~790,000 B.P. (years before the present; taken as 1950 CE) (1,2) or even earlier (3,4). Since then, fuel has become an indispensable resource in subsistence, particularly considering that making fire was vital for early humans to better adapt to the living environment, and has probably profoundly affected their physiology and social organization (5)(6)(7)(8). Subsequently, wood, charcoal, and dung were widely used as fuels. Coal became more important in the Chinese Song Dynasty (990 to 671 B.P.) (9) and played an obbligato role in the European Industrial Revolution (10). ...
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Coal has long fueled human civilizations. The history of systematic coal fuel exploitation has been traced back to the late third millennium before present (post-2500 B.P.). Although sporadic combustion of coal for fuel was reported in some prehistoric archaeological sites, evidence for the systematic exploitation of coal for fuel before 2500 B.P. remains lacking. Here, we report comprehensive understanding for the earliest systematic exploitation of coal for fuel at the Jirentaigoukou site in Xinjiang, northwestern China, at ~3600 B.P. The main body of the site witnessed systematic exploitation of bituminous coals, illustrating a complete chaîne opératoire with selective mining, planned storage, and extensive combustion. Our results transform the knowledge of energy history by extending the upper limit of the systematic exploitation of coal for fuel by approximately a millennium, and provide a precedent of energy transition under intense conflict between social demand and environmental deterioration.
Chapter
For eons, the indigenous peopleIndigenous people of BangladeshBangladesh have lived in isolated locations away from the modern benefits of health and nutritionNutrition care. Despite initiatives by government and development partners over three decades to bring them modern services, the majority of the indigenous population are living outside the coverage and are depending on their indigenous knowledgeIndigenous knowledge of health, nutritionNutrition, and environmentEnvironments to survive environmental shocks and hazards. Our study tried to understand the effectiveness of their related knowledge and practices from a modern scientific perspective and examined the possibility of adopting them into the mainstream Bangladeshi society. We conducted 23 in-depth interviews with members of selected indigenous tribes for 1 month, in addition to literature review. The study result found a wide range of traditional health, nutritionNutrition, and environmental practices used by the indigenous communities of BangladeshBangladesh that were passed through the generations. Some of the practices were found to have confirmed positive health and nutritionNutrition benefits, which deserve further research and possible integrationIntegration into modern care. There were other practices identified that are hazardous for health, and, consequently, not recommended for integrativeIntegrative care. Moreover, we recommend that the scope of scientific knowledgeScientific knowledge and modern practices should be expanded among the indigenous peopleIndigenous people giving equal importance to the communities of hill tracts and the plain lands. It is recommended that integrativeIntegrative care can be achieved best through the development of an indigenous communities-focused operation plan in Health, Population and NutritionNutrition Sector Development Program (HPNSDP) for BangladeshBangladesh to improve health services in the region. Scientifically accepted good health, nutritionNutrition, and environmental practices should be adopted in the mainstream societies of BangladeshBangladesh to expand the scope of services related to health, nutritionNutrition, and environmentEnvironments.
Chapter
Evolutionary psychiatry attempts to explain and examine the development and prevalence of psychiatric disorders through the lens of evolutionary and adaptationist theories. In this edited volume, leading international evolutionary scholars present a variety of Darwinian perspectives that will encourage readers to consider 'why' as well as 'how' mental disorders arise. Using insights from comparative animal evolution, ethology, anthropology, culture, philosophy and other humanities, evolutionary thinking helps us to re-evaluate psychiatric epidemiology, genetics, biochemistry and psychology. It seeks explanations for persistent heritable traits shaped by selection and other evolutionary processes, and reviews traits and disorders using phylogenetic history and insights from the neurosciences as well as the effects of the modern environment. By bridging the gap between social and biological approaches to psychiatry, and encouraging bringing the evolutionary perspective into mainstream psychiatry, this book will help to inspire new avenues of research into the causation and treatment of mental disorders.
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Ritual alterations of consciousness are a virtual universal of human cultures, reflecting a basic human drive generally considered of central importance to religion and spiritual practices. Cross-cultural perspectives show both similarities in the experiences of altered consciousness (AC) that implicate biological factors as the basis for similarities across cultures, time, and space, as well as cultural differences in the manifestations of these potentials that implicate social factors. Individual and group experiences of altered consciousness may vary in many ways, but it is commonal-ities and recurrent patterns, rather than unique differences, that are crucial to understanding AC. This introduction reviews evidence for the universal manifestation of altered consciousness. This universal manifestation is not well explained in the classic paradigms of altered states of consciousness that emphasize their individual nature. In contrast, a biological approach to consciousness helps to situate altered consciousness within human nature. This perspective provides a foundation for an approach that characterizes AC in terms of an integrative mode of consciousness that reflects systemic features of brain functioning. This integrative mode of consciousness is typified in theta wave patterns that synchronize the frontal cortex with discharges from lower brain structures. This integration of ancient brain functions into the frontal cortex explains many of the key features of AC.
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The data includes measures collected for the two experiments reported in “False-Positive Psychology” [1] where listening to a randomly assigned song made people feel younger (Study 1) or actually be younger (Study 2). These data are useful because they illustrate inflations of false positive rates due to flexibility in data collection, analysis, and reporting of results. Data are useful for educational purposes.
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The mastery of fire is a great human achievement which has helped shape our species. This chapter addresses the wider importance of fire, arguing that it is part of a fundamental motor of human evolution, deeply tied into our biology as well as economy and technology, and indeed a motor of the social brain. It seems likely that fire was involved in this nexus from a very early period, probably back to the time of increases in human brain size in the early Pleistocene, and indeed that it may have been a necessity for the subsequent physical evolutionary and social developments in Homo. Fire may be associated so strongly with imagery, imagination and symbolism in the modern world as a result of its primary role in effecting transformation of materials, and acting to link various strands of material culture.
Book
We've all witnessed this moment: a dog, a cat, or another animal reacting to its own reflection in the mirror, treating it as another animal to be played with or confronted. As human beings, we take self-recognition for granted, but this seemingly simple ability represents one of the most complex mysteries of neuroscience. The Face in the Mirror takes readers on a lively tour of the neurological, anthropological, and psychological roots of self-recognition -- from the intricate network in the brain that enables higher primates to recognize their image to complex, self-related emotions such as humor, embarrassment, and jealousy that play a crucial role in our evolution and survival. From animals who share our ability for self-recognition to case studies of patients who no longer recognize who they are, the authors examine some of the latest evidence on a subject that has puzzled philosophers and scientists for millennia -- how do we know who we are?
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Drawing together evidence from a wide range of scientific disciplines, this book presents an evolutionary history of religion. That history begins with the social lives and rituals of our primate ancestors. As our ancestors' social world grew increasingly complex, their mental powers grew in concert. Among these mental powers was an increasingly sophisticated imagination. A supernatural world filled with gods, spirits, and ancestors was an outgrowth of that imagination-especially children's imagination. Belief in the supernatural provided important adaptive benefits. Religion's initial adaptive benefit was its power to heal. Quickly, though, this benefit was augmented by religion's power to create highly cooperative and cohesive groups. So significant were these benefits that eventually human groups bonded together by religion out-competed all other groups and literally conquered the world. The book argues that at its core, religion is relational-it represents a supernatural extension of the human social world. Far from just a frivolous adornment, this expanded social world holds the key to what made us human.