Evidence for a geometric brain module suggested by William's syndrome defect

Context from the introduction by Lakusta et al.

When rats, human toddlers, or adults are disoriented in a chamber, they search for targets using geometric properties of the layout, often ignoring quite salient nongeometric cues. This pattern has led scientists to hypothesize that reorientation in animals (including humans) is guided by a cognitive module that engages geometric properties of layouts such as the lengths of surfaces, the angles of their intersections, and geometric sense (i.e., “left-” and “right-ness”), but does not engage nongeometric information such as surface color.

The authors find that geometric reorientation abilities are specifically impaired in Williams Syndrome patients. (Williams syndrome results from a microdeletion in chromosome 7q11.23. People with the syndrome have mild to moderate retardation and highly selective but severe impairment in a range of spatial tasks that normally engage parietal and other dorsal stream functions of the brain.)  Here is their abstract:

The capacity to reorient in one’s environment is a fundamental part of the spatial cognitive systems of both humans and nonhuman species. Abundant literature has shown that human adults and toddlers, rats, chicks, and fish accomplish reorientation through the construction and use of geometric representations of surrounding layouts, including the lengths of surfaces and their intersection. Does the development of this reorientation system rely on specific genes and their action in brain development? We tested reorientation in individuals who have Williams syndrome (WS), a genetic disorder that results in abnormalities of hippocampal and parietal areas of the brain known to be involved in reorientation. We found that in a rectangular chamber devoid of surface feature information, WS individuals do not use the geometry of the chamber to reorient, failing to find a hidden object. The failure among people with WS cannot be explained by more general deficits in visual-spatial working memory, as the same individuals performed at ceiling in a similar task in which they were not disoriented. We also found that performance among people with WS improves in a rectangular chamber with one blue wall, suggesting that some individuals with WS can use the blue wall feature to locate the hidden object. These results show that the geometric system used for reorientation in humans can be selectively damaged by specific genetic and neural abnormalities in humans.

Human pheromones - androstenol activates hypothalamus in women.

There is continuing debate over whether, and to what extent, we humans (like other mammals) might use body odors secreted from our skin in signaling sexual attraction, aggression, submission, etc.  Several progesterone derivatives have been shown to activate regions of the thalamus and hypothalamus, and the activations are differentiated with respect to sex and sexual orientation of the smeller in relation to the respective compounds.   Slavic et al. asked whether compounds actually released by our bodies have pheromone properties, and focused on highly volatile androstenol, which is found (primarily in males), in sweat, urine, plasma and saliva. They found that smelling androstenol (unlike several common odors) causes activation of a portion of the hypothalamus in women that animal data suggests mediates pheromone triggered mating behavior. (The article is open access, and you can see the brain imaging data there.)

Reward centers in men activated by optimal hip-to-waist ratio in women

Observations from Platek and Singh add to the evolutionary psychologists' discussion of determinants of men's sexual preferences. They take male preference for lower hip waist ratio in females (as indicative of reproductive quality) to be culturally universal, but I recall debate on this point, and indeed find that debate covered by cited references (17,18) at the end of the article. Their core observation is that when men view photographs of women after and before plastic surgery to achieve an optimal (~0.7) waist to hip ratio (with redistributed body fat but relatively unaffected body mass index), an increase in activation of brain rewards centers can be observed. They suggest their observations "are the first description of a neural correlate implicating waist to hip ratio as a putative honest biological signal of female reproductive viability and its effects on men's neurological processing."

Is the internet making us smarter or dumber?

During happy hour at my local watering hole, I frequently pull out my iPhone and do a bit of random web cruising. Several nights ago this yielded this piece on effects of internet use on our intelligence, suggesting extensive internet use makes us different, but not dumb. The article cites a Pew Study reporting, contra an influential article by Nicholas Carr, that 76 percent of the respondents said they agree that by 2020, "people’s use of the Internet has enhanced human intelligence; as people are allowed unprecedented access to more information, they become smarter and make better choices. The article also relays the opinions of a number of other futurists.

Universal nonverbal vocal communication of negative, but not positive, emotions.

Here is a fascinating open access article well worth having a look at:

Emotional signals are crucial for sharing important information, with conspecifics, for example, to warn humans of danger. Humans use a range of different cues to communicate to others how they feel, including facial, vocal, and gestural signals. We examined the recognition of nonverbal emotional vocalizations, such as screams and laughs, across two dramatically different cultural groups. Western participants were compared to individuals from remote, culturally isolated Namibian villages. Vocalizations communicating the so-called “basic emotions” (anger, disgust, fear, joy, sadness, and surprise) were bidirectionally recognized. In contrast, a set of additional emotions was only recognized within, but not across, cultural boundaries. Our findings indicate that a number of primarily negative emotions have vocalizations that can be recognized across cultures, while most positive emotions are communicated with culture-specific signals.

Holy surgery and the spiritual brain.

Over the past several years I've done a number of posts on brain correlates of spirituality, in particular work on lesions or temporal lobe seizures that induce mystical or spiritual states (click the religion topic in the left column to find them). Urgesi et al. have now done a clinical study on selective cortical lesions that modulate human self transcendence. They 88 brain cancer patients to fill out a widely used personality questionnaire before and after surgery to remove their tumors. One section of the test measured "self transcendence." It asked respondents, for example, about their tendency to become so absorbed in an activity that they lose track of time and place and whether they feel a strong spiritual connection with other people or with nature. They found that selective damage to left and right inferior posterior parietal regions induced a specific increase of self-transcendence. Other studies have found that some of the same regions become active during prayer and meditation. These posterior parietal brain regions have been implicated in providing awareness of the body's position and location in space.

Figure - Lesion Correlates of Increased and Decreased Self Transcendence. The authors found two clusters of voxels located in the left inferior parietal lobe (L-IPL; A) and in the right angular gyrus (R-AG; B) whose damage was associated with a significant ST increase.

The 'cutaneous rabbit' hops outside of the body!

A well known demonstration of how our brain makes assumptions about what is happening 'out there' on the basis of very limited input is the 'Cutaneous Rabbit' demonstration. If rapid sequential taps are delivered to two points on our skin, we also feel sequential taps at points intermediate between the two, as if a small rabbit were hopping along our skin. The assumption has been that this illusion is link to our somatotopic sensory cortex, which continuously maps the skin surface. Miyazaki et al. show that this illusion can be moved to an external object - a stick held between our left and right index fingers. Here is the abstract from their open access article:

Rapid sequential taps delivered first to one location and then to another on the skin create the somatosensory illusion that the tapping is occurring at intermediate locations between the actual stimulus sites, as if a small rabbit were hopping along the skin from the first site to the second (called the "cutaneous rabbit"). Previous behavioral studies have attributed this illusion to the early unimodal somatosensory body map. A functional magnetic resonance imaging study recently confirmed the association of the illusion with somatotopic activity in the primary somatosensory cortex. Thus, the cutaneous rabbit illusion has been confined to one's own body. In the present paper, however, we show that the cutaneous rabbit can "hop out of the body" onto an external object held by the subject. We delivered rapid sequential taps to the left and right index fingers. When the subjects held a stick such that it was laid across the tips of their index fingers and received the taps via the stick, they reported sensing the illusory taps in the space between the actual stimulus locations (i.e., along the stick). This suggests that the cutaneous rabbit effect involves not only the intrinsic somatotopic representation but also the representation of the extended body schema that results from body–object interactions.

Some friday morning Mozart

Working with retired professional pianist David Goldberger, I'm preparing for a 4-hands recital on Sunday, March 7 in Fort Lauderdale. I decided to make a few rehearsal recordings, to be eventually replaced by a final version. The video below is of a palatable, but we think much less than optimal, run through of the Allegro (first movement) of Mozart's Piano Sonata for 4-hands, K. 358. We will also be doing the Schubert Fantasy for 4-hands.

Effect of socioeconomic status on increase in stress hormones over time.

A sobering account from Chen et al.:

Disparities by socioeconomic status (SES) are seen for numerous mental and physical illnesses, and yet understanding of the pathways to health disparities is limited. We tested whether SES alters longitudinal trajectories of cortisol output and what types of psychosocial factors could account for these links. Fifty healthy children collected saliva samples (four times per day for 2 days) at 6-month intervals for 2 years. At baseline, families were interviewed about SES and psychosocial factors. Lower-SES children displayed greater 2-year increases in daily cortisol output compared with higher-SES children. These effects were partially mediated by children’s perceptions of threat and by family chaos. These findings may help explain, and provide some first steps toward ameliorating, low-SES children’s vulnerability to health problems later in life by identifying the tendency to perceive threat in ambiguous situations and experiences of chaos as factors that link low SES to 2-year hormonal trajectories.

Female teachers can transmit math anxiety to girls

Beilock et al. make some interesting observations:

People’s fear and anxiety about doing math—over and above actual math ability—can be an impediment to their math achievement. We show that when the math-anxious individuals are female elementary school teachers, their math anxiety carries negative consequences for the math achievement of their female students. Early elementary school teachers in the United States are almost exclusively female (more than 90%), and we provide evidence that these female teachers’ anxieties relate to girls’ math achievement via girls’ beliefs about who is good at math. First- and second-grade female teachers completed measures of math anxiety. The math achievement of the students in these teachers’ classrooms was also assessed. There was no relation between a teacher’s math anxiety and her students’ math achievement at the beginning of the school year. By the school year’s end, however, the more anxious teachers were about math, the more likely girls (but not boys) were to endorse the commonly held stereotype that “boys are good at math, and girls are good at reading” and the lower these girls’ math achievement. Indeed, by the end of the school year, girls who endorsed this stereotype had significantly worse math achievement than girls who did not and than boys overall. In early elementary school, where the teachers are almost all female, teachers’ math anxiety carries consequences for girls’ math achievement by influencing girls’ beliefs about who is good at math.

More on conservative versus liberal brains.

Nicholas Kristoff does a nice piece on a topic I have done several previous posts on - fundamental differences in the wiring of conservative versus liberal brains - the central observation being that conservatives feel threat and revulsion much more readily than liberals, with corresponding physiological changes measured, for example, by the startle blink reflex or skin conductance. Kristoff discusses work showing a remarkably strong correlation between state attitudes toward spanking children and voting patterns. Essentially, spanking states go Republican, while those with more timeouts go Democratic.

Spankers tend to see the world in stark, black-and-white terms, perceive the social order as vulnerable or under attack, tend to make strong distinctions between “us” and “them,” and emphasize order and muscular responses to threats. Parents favoring timeouts feel more comfortable with ambiguities, sense less threat, embrace minority groups — and are less prone to disgust when they see a man eating worms.

And, I thought this bit was interesting:

I moaned to the scholars that their research was utterly dispiriting for those of us in the opinion business. After all, it’s extra challenging to try to change people’s minds if they may not even share our hard-wiring. Are people who are “wrong” on the issues beyond redemption, because of their physiological inability to help themselves?..Professors Hetherington and Smith dismissed my whining and were more sanguine. For starters, they note that physiological differences are probably found among the extremes on each side, while political battles are fought in the middle. Indeed, these studies may be useful in determining what arguments to deploy against the other side...“What research like ours may help with is in figuring out how to construct an argument in a way that is going to meaningfully connect with those on the other side,” Dr. Smith said.

Conservatives may be more responsive to health reform, he suggested, if it is framed as a national security argument. For example, American companies complain about the difficulty of competing with foreign companies that don’t have to pay for employee medical coverage. In that sense, our existing health care system leaves us vulnerable...That foreign threat might make conservatives sweat so much that maybe, just maybe, they’d consider revisiting the issue.

Grumpy people may be more evolved

My son pointed me to work by Wobber et al.  which makes me feel much better about my curmudgeonly nature.  They compared the behavior of Chimpanzees, who can be quite grumpy, that that of Bonobos, who maintain childlike playfulness throughout their lives.  They suggest the chimps' ability to put aside their sociability is one of the reasons they are more intelligent and civilized than their genetically similar great ape cousins.  Perhaps being aggressive, intolerant and short-tempered could be a sign of a more advanced nature! Here is their abstract:

Phenotypic changes between species can occur when evolution shapes development. Here, we tested whether differences in the social behavior and cognition of bonobos and chimpanzees derive from shifts in their ontogeny, looking at behaviors pertaining to feeding competition in particular. We found that as chimpanzees (n = 30) reached adulthood, they became increasingly intolerant of sharing food, whereas adult bonobos (n = 24) maintained high, juvenile levels of food-related tolerance. We also investigated the ontogeny of inhibition during tasks that simulated feeding competition. In two different tests, we found that bonobos (n = 30) exhibited developmental delays relative to chimpanzees (n = 29) in the acquisition of social inhibition, with these differences resulting in less skill among adult bonobos. The results suggest that these social and cognitive differences between two closely related species result from evolutionary changes in brain development.

Cat Turf War

My apologies (and this surely falls under the 'random curious stuff' category) but I can't resist passing on this hysterical cat video.

Better to react than to act.

In ScienceNOW Tim Wogan points to recent work by Welchman et al.  showing that when it comes to execution of our movements, reaction beats intention by about 10%.

Have you ever noticed that the first cowboy to draw his gun in a Hollywood Western is invariably the one to get shot? Nobel prize–winning physicist Niels Bohr did, once arranging mock duels to test the validity of this cinematic curiosity.

Welchman's team organized simulated "gunfights" in the laboratory, with pairs of volunteers competing against each other to push three buttons on a computer console in a particular order. The researchers observed that the time interval between when players removed their hands from the first button and when they pressed the final button was on average 9% shorter for the players who reacted to an opponent moving first. However, those who reacted to a first move were more likely to make an error, presssing the buttons in the wrong order. Welchman speculates that this rapid, if somewhat inaccurate, response system may have evolved to help humans deal with danger, when immediate reaction is essential and the risk of an error worth taking.

Dialing the desired emotions in your music...

One evolutionary rationale for the origin of music is that it enhances and amplifies basic emotional states to amplify social bonding and cohesion, creating an emotional resonance that spreads through and binds a group to share joy, anger, sadness, kindness, etc. Thus I was fascinated upon receiving an email from folks who have made a new widget that appears to tap some very ancient roots in a high-tech way - an iPhone App called Moodagent that lets you adjust touchscreen sliders labeled Sensual, Tender, Joy, Aggressive and Tempo to create playlists whose musical items correspond to the emotional mix you have specified. I have several thousand items in my iTunes music library, mostly classical performances I don't even remember putting there, totaling many more gigabytes than the iPhone has, and this App, with the assistance of a small bit of downloaded software, manages to scan my collection, and offer any of its items to a list of 25 pieces selected to fit the emotional mix I have requested. (I have no idea how it does this - something about 'the cloud'). I'm discovering all sort of music I didn't realize I had.  And, having been a person who has resolutely refused to work while listening to music I sit here (like my adult kids always have) doing just that, with a playlist having a high 'tender' setting.  Now let's see what happens if I ramp up the 'sensual setting.'  Here is a demo video:



Added note: A bit of web cruising yields this information on how that small downloaded App (Moodagent Profilter) has managed to let Moodagent draw items from my whole iTunes library.

Moodagent Profiler desktop app, like Apple’s Genius function, goes through your iTunes library and uploads anonymous information about your iTunes tracks to the Moodagent server. The more people who use the app and index their music, the better Moodagent’s database will get.

Lusting while loathing...

An interesting open access article from Litt (something you knew already, but psychologists gotta have something to measure!):

We show how being “jilted”—that is, being thwarted from obtaining a desired outcome—can concurrently increase desire to obtain the outcome, but reduce its actual attractiveness. Thus, people can come to both want something more and like it less. Two experiments illustrate such disjunctions following jilting experiences. In Experiment 1, participants who failed to win a prize were willing to pay more for it than those who won it, but were also more likely to trade it away when they ultimately obtained it. In Experiment 2, failure to obtain an expected reward led to increased choice, but also negatively biased evaluation, of an item that was merely similar to that reward. Such disjunctions were exhibited particularly by individuals low in intensity of felt affect, a finding supporting an emotional basis for relative harmonization of wanting and liking. These results demonstrate how dissociable psychological subsystems for wanting and liking can be driven in opposing directions.

A chemical test for disturbed relationship?

MindBlog has done a number of posts on behavioral effects of oxytocin and vasopressin in humans (enter the terms in the search box in the left column to see them). Taylor et al. now show, in an open access article, that they may be biomarkers of distressed relationships:

Young adults in couple (pair-bond) relationships reported on the positive and negative aspects of their relationships and had blood drawn and assayed for oxytocin and vasopressin. Elevated plasma oxytocin was associated with distress in the pair-bond relationship for women, but not for men. Vasopressin, which is closely related to oxytocin in molecular structure and significantly related to male pair-bond behavior in animal studies, was elevated in men experiencing distress in the pair-bond relationship, but not in women. Controlling for estradiol and testosterone did not alter these findings. We conclude that plasma oxytocin in women and plasma vasopressin in men may be biomarkers of distressed pair-bond relationships.

Abstract thoughts move muscles.

Movements of our muscles influence our thoughts and emotions. People given neutral bland instructions to contract the specific face muscles that make a smile find it harder to generate a feeling of anger when requested to do so, and instruction to move the muscles that make an angry frown make it harder to follow a subsequent instruction to feel friendly or happy. Havas has found that blocking a frown can actually prevent a bad mood.  Natalie Angier summarizes several studies that show the opposite: how thoughts influence our muscle movements in subtle ways.  Miles et al., for example, show that when we thing of events in the future, our bodies move slightly forward, while thinking of past events causes them to move slightly backwards. Their observations are consistent with theories of "embodied cognition," in this case mental time travel may be represented in the sensorimotor systems that regulate human movement. The metaphorical “arrow of time” may be grounded in a processing architecture that integrates temporal and spatial information in a directional manner (i.e., past = back, future = forward).

Angier also notes other work on embodied cognition that I have mentioned - Students who held a hot cup of coffee in their hand were more likely to evaluate a target person as being warm and friendly than those holding a cold cup of coffee.  She notes work (this post) showing that a warm versus cold stare causes subject to evaluate the temperature of a room as warmer.  Finally she points to work (this post) showing our bodies conflate weight with greater importance or value.  (...almost makes you think that  both Angier and Bownds scan the contents of the journal "Psychological Science.")

The 4th anniversary of Deric's MindBlog

As year five of this blog starts, I find it hard to believe that I have banged out over 2,000 postings, that the blog has ~1,500 RSS feed subscribers, and is seriously engaged by 300-400 people on an average day.

(The figure is a Feedburner report, starting in July 2006.  The green line is the number of RSS subscribers, the blue indicates significant engagement, the amplitude being the weekday (new posts) - weekend (no new posts) difference).

About this time of year I usually cycle through an identity crisis regarding what kind of thinking and writing I want to do, how much energy to put into MindBlog.  Sometimes external forces nudge my efforts.  I recently got a curious invitation to an international Cognitive Neuroscience meeting in Istanbul next May 18-20.  The request was that I both present a piano recital and also give a talk on the mind.  I'm now working on the talk ("Who wants to know? - the nature of our subjective "I"), deciding on the music, and will eventually put the talk on my website, with a podcast version on this blog.  I've done a few previous podcasts (see left column of blog), but haven't really gotten into it.  I don't listen to podcasts, they seem so much less efficient than just reading.  I started to play with Twitter (left column), but aside from a few spurts of activity, I also haven't gotten into it.

Ever since the 1999 publication of my book, The Biology of Mind, I have puttered with the idea of another book. This first book had been a 'crossover' effort, written to be useful both for college course instruction and also for the educated layperson. It was reasonably successful, got some good reviews, and by now has sold ~ 9,000 copies. For the first year or two after its publication both I and the reviewers assumed that there would be a second revised edition.

But as I began to organize an updated version over the next several years, I became tempted by the prospect of doing a pure trade book, not a textbook. I got as far as a fairly complete book outline and design. Then I toyed with the idea of a short paragraph-a-day popular book, a bit of test writing being Mindstuff: bon-bons for the curious user posted on my website in 2002. Then in 2005 I attempted a still short but more continuous text: Mindstuff: a guide for the curious user. (On re-reading, it comes off as ponderous and impenetrable.) None of these efforts got to the level of seriously writing for publication - mainly because I was observing an exponential increase in the number of popular books on the mind, and thought it very likely that my effort would be lost in the noise.

I started Deric's MindBlog in early 2006, after reading a New York Times article on the blog phenomenon, and found myself reaching a larger audience than the previous writing efforts had generated, with much more feedback and interaction. Generating this blog provided a very useful excuse for doing all the reading I was doing anyway, for my own pleasure and stimulation - I could feel less self-indulgent if I was passing some of the material on. 

The problem with the blog gig, which I have mentioned before, is that it is a very episodic, present-centered, non-cumulative activity - a very different mindset from the deeper and more continuous thinking that goes into doing a book. I don't think I have the time, motivation, or energy to do both kinds of activities.

This thinking-out-loud gets me to the point of rambling further about a book title that has been popping into my head for at least the last ten years: "The 100 Millisecond Manager." (a riff on the title the popular book of the early 1980's by Blanchard and Johnson, "The One Minute Manager.") The gist of the argument would be that given in the "Guide" section of the 2005 writing I mentioned above, and actually in Chapter 12 of my book, Figure 12-7.

It might make the strident assertion that the most important thing that matters in regulating our thoughts, feelings, and actions is their first 100-200 msec in the brain, which is when the levers and pulleys are actually doing their thing. It would be a nuts and bolts approach to altering - or at least inhibiting - self limiting behaviors. It would suggest that a central trick is to avoid taking on on the ‘enormity of it all,’ and instead use a variety of techniques to get our awareness down to the normally invisible 100-200 msec time interval in which our actions are being programmed. Here we are talking mechanical, not ideological; this is where all the limbic routines that result from life script, self image, temperament, etc., actually get their start-up. The suggestion is that you can short circuit the whole process if you simply bring awareness to the level of observing the moments during which a behavior switches on, and can sometimes say “I don’t think so.”

"The 100 msec Manager" has gone through the ‘this could be a book’  cycle several times over the past ten years, the actual execution then bogging down as I actually got into description of the underlying science and techniques for expanding awareness. I keep searching for keys to making it feisty, punchy, accessible, and attractive to readers. I note the enormous number of books out there on meditation, relaxation, etc. that are all really addressing the same core processes in different ways. How attractive or effective would be an approach that didn't have the slightest whiff of 'spirituality' or 'purpose' be? (I think that spirituality and purpose are human inventions, culturally evolved psychologies, not shared with other animals, that help humans pass on their genes.)

So.... for the moment all this waffling brings me back to thinking that just doing this blog isn't such a bad deal after all.

Religiosity tied to socioeconomic status.

Gregory Paul makes an interesting comment on an article by Cullota that was the subject of my Nov. 17 post.  I think his point that belief in gods and an afterlife is unlikely to be a "strongly genetically programmed result of major selective evolutionary pressures such as social cohesion" is a good one.   But, I assume he would agree that there is genetic/development programming of things like the facial muscles that are specialized for signaling affiliative gestures that are universal across cultures. Here is his letter:

The Science News Focus story "On the origin of religion" (E. Culotta, 6 November 2009, p. 784) did not incorporate the growing body of psychosociological research that is revealing the crucial role of socioeconomics in the origin and popularity of religion, as well as in creationism (1–6). Some hunter-gatherers have minimal religion (7), and those who do not believe in the gods and an afterlife have spontaneously expanded in prosperous democracies until they are the majority in some nations, such as France, Sweden, and Denmark (1, 3, 4). Because religion is not universal, as implied in the News Focus article, serious religiosity cannot be the strongly genetically programmed result of major selective evolutionary pressures such as social cohesion (8).

In modern nations, nonreligion and the acceptance of evolution become popular when the middle class majority feels sufficiently secure and safe, thanks to low income inequality, universal health care, job and retirement security, and low rates of lethal crime; this has occurred to greater and lesser degrees in most first-world countries, from Japan to Scandinavia (1–6). Religion thrives when the majority seek the aid and protection of supernatural powers because they are impoverished, as in the third- and second-world countries or, in the case of the United States (the most religious and creationist first-world country), because the majority of Americans fear losing their middle-class status as a result of limited government support, high levels of social pathology, and intense economic competition and income disparity (1–6). Prosperous modernity is proving to be the nemesis of religion.

References

* 1. G. Paul, Evol. Psychol. 7, 398 (2009); www.epjournal.net/filestore/EP07398441_c.pdf.
* 2. T. Rees, J. Relig. Soc. 11 (2009); moses.creighton.edu/JRS/2009/2009-17.html.
* 3. P. Zuckerman, Soc. Compass 3, 949 (2009). [CrossRef]
* 4. P. Norris, R. Inghelart, Sacred and Secular (Cambridge Univ. Press, Cambridge, 2004).
* 5. A. Gill, E. Lundsgaarde, Rational. Soc. 16, 399 (2004). [CrossRef]
* 6. S. Verweii, P. Ester, R. Naata, J. Sci. Study Relig. 36, 309 (1997). [CrossRef] [Web of Science]
* 7. F. Marlowe, in Ethnicity, Hunter-Gatherers, and the "Other," S. Kent , Ed. (Smithsonian Institute Press, Washington, DC, 2002), pp. 247–281.
* 8. C. N. Wade, The Faith Instinct (Penguin, New York, 2009).