A science debate for presidential candidates?

A note for this day of the Iowa presidential primary...I have signed on with many others at Science Debate 2008 to urge the candidates to debate issues in science and technology, and would urge readers of this blog to do the same. Here are some comments by John Tierney.

Liberals are smarter than conservatives...?

A British study by Deary et al. titled "Bright Children become Enlightened Adults" (Psychological Science, Volume 19 pp. 1-6, January 2008) shows a correlation between general intelligence (g) at age 10 and liberal and anti-traditional social attitudes at age 30...

We examined the prospective association between general intelligence (g) at age 10 and liberal and antitraditional social attitudes at age 30 in a large (N = 7,070), representative sample of the British population born in 1970. Statistical analyses identified a general latent trait underlying attitudes that are antiracist, pro-working women, socially liberal, and trusting in the democratic political system. There was a strong association between higher g at age 10 and more liberal and antitraditional attitudes at age 30; this association was mediated partly via educational qualifications, but not at all via occupational social class. Very similar results were obtained for men and women. People in less professional occupations—and whose parents had been in less professional occupations—were less trusting of the democratic political system. This study confirms social attitudes as a major, novel field of adult human activity that is related to childhood intelligence differences.

Alarms and Anxiety in 2008 - guaranteed

John Tierney does a very nice piece in the Jan 1 NY Times Science section describing how activists, journalists and publicity-savvy scientists (called availability entrepreneurs by social scientists) selectively monitor the globe looking for newsworthy evidence of a new form of sinfulness, burning fossil fuels. Some clips from his text:

A year ago, British meteorologists made headlines predicting that the buildup of greenhouse gases would help make 2007 the hottest year on record. At year’s end, even though the British scientists reported the global temperature average was not a new record — it was actually lower than any year since 2001 — the BBC confidently proclaimed, “2007 Data Confirms Warming Trend.”

When the Arctic sea ice last year hit the lowest level ever recorded by satellites, it was big news and heralded as a sign that the whole planet was warming. When the Antarctic sea ice last year reached the highest level ever recorded by satellites, it was pretty much ignored. A large part of Antarctica has been cooling recently, but most coverage of that continent has focused on one small part that has warmed.

When Hurricane Katrina flooded New Orleans in 2005, it was supposed to be a harbinger of the stormier world predicted by some climate modelers. When the next two hurricane seasons were fairly calm — by some measures, last season in the Northern Hemisphere was the calmest in three decades — the availability entrepreneurs changed the subject. Droughts in California and Australia became the new harbingers of climate change (never mind that a warmer planet is projected to have more, not less, precipitation over all).

The most charitable excuse for this bias in weather divination is that the entrepreneurs are trying to offset another bias. The planet has indeed gotten warmer, and it is projected to keep warming because of greenhouse emissions, but this process is too slow to make much impact on the public.

When judging risks, we often go wrong by using what’s called the availability heuristic: we gauge a danger according to how many examples of it are readily available in our minds. Thus we overestimate the odds of dying in a terrorist attack or a plane crash because we’ve seen such dramatic deaths so often on television; we underestimate the risks of dying from a stroke because we don’t have so many vivid images readily available.

Slow warming doesn’t make for memorable images on television or in people’s minds, so activists, journalists and scientists have looked to hurricanes, wild fires and starving polar bears instead. They have used these images to start an “availability cascade,” a term coined by Timur Kuran, a professor of economics and law at the University of Southern California, and Cass R. Sunstein, a law professor at the University of Chicago.

The availability cascade is a self-perpetuating process: the more attention a danger gets, the more worried people become, leading to more news coverage and more fear. Once the images of Sept. 11 made terrorism seem a major threat, the press and the police lavished attention on potential new attacks and supposed plots. After Three Mile Island and “The China Syndrome,” minor malfunctions at nuclear power plants suddenly became newsworthy.

...Once a cascade is under way, it becomes tough to sort out risks because experts become reluctant to dispute the popular wisdom, and are ignored if they do. Now that the melting Arctic has become the symbol of global warming, there’s not much interest in hearing other explanations of why the ice is melting — or why the globe’s other pole isn’t melting, too.

Nature versus Nurture in Ventral Visual Cortex

Polk et al. do functional magnetic resonance imaging of monozygotic and dizygotic twins to show that genetics play a significant role in determining the cortical response to faces and places, more so than to orthographic stimuli (chairs or pseudowords). Here is their abstract, a paragraph from their concluding section and one figure from the paper.

Using functional magnetic resonance imaging, we estimated neural activity in twins to study genetic influences on the cortical response to categories of visual stimuli (faces, places, and pseudowords) that are known to elicit distinct patterns of activity in ventral visual cortex. The neural activity patterns in monozygotic twins were significantly more similar than in dizygotic twins for the face and place stimuli, but there was no effect of zygosity for pseudowords (or chairs, a control category). These results demonstrate that genetics play a significant role in determining the cortical response to faces and places, but play a significantly smaller role (if any) in the response to orthographic stimuli.


Figure legend: Patterns of estimated neural activity when viewing the four stimulus categories (axial slice). Functional activation maps were computed for the four contrasts of interest (faces, houses, pseudowords, and chairs relative to the phase-scrambled control condition), and the similarity measures (r) between these functional maps were computed for each twin pair. (Click on figure to enlarge)

The results of this study demonstrate that genetics play a significant role in determining the cortical response to faces and places. Of course, these findings do not imply that experience plays no role in determining the observed activity. To take just one example, genes that affect social behavior could potentially lead some people to look at faces and places more than other people, and the resulting difference in experience could lead to changes in the neural circuitry (we thank one of the anonymous reviewers for this example). The results simply demonstrate that genetics do play a crucial role. The results also show that genetics play a significantly smaller role in determining the cortical response to visually presented orthographic stimuli. Overall, the findings are consistent with the view that the cortical substrates of face recognition and place recognition are partially innately specified, but that the cortical response to orthographic stimuli is more dependent on experience. Face and place recognition are older than reading on an evolutionary scale, they are shared with other species, and they provide a clearer adaptive advantage. It is therefore plausible that evolution would shape the cortical response to faces and places, but not orthographic stimuli.

Experimental Philosophy - moving out of the armchair?

The Dec. 9 New York Times Magazine has a fascinating article by Kwame Appiah that I have been meaning to mention, on the new philosophical trend of designing explicit experiments - many to probe the classic philosophical concept of intentionality. The following sort of result is now called the "Knobe effect" after the philosophy graduate student who devised the experiment (and the article describes a number of further experiments):

Suppose the chairman of a company has to decide whether to adopt a new program. It would increase profits and help the environment too. “I don’t care at all about helping the environment,” the chairman says. “I just want to make as much profit as I can. Let’s start the new program.” Would you say that the chairman intended to help the environment?

O.K., same circumstance. Except this time the program would harm the environment. The chairman, who still couldn’t care less about the environment, authorizes the program in order to get those profits. As expected, the bottom line goes up, the environment goes down. Would you say the chairman harmed the environment intentionally?

I don’t know where you ended up, but in one survey, only 23 percent of people said that the chairman in the first situation had intentionally helped the environment. When they had to think about the second situation, though, fully 82 percent thought that the chairman had intentionally harmed the environment. There’s plenty to be said about these interestingly asymmetrical results.

... is it a good thing that we attribute intention in the curious way that we do, and if so, why? (Is the Knobe effect a bug or a feature?) You can conduct more research to try to clarify matters, but you’re left having to interpret the findings; they don’t interpret themselves. There always comes a point where the clipboards and questionnaires and M.R.I. scans have to be put aside. To sort things out, it seems, another powerful instrument is needed. Let’s see — there’s one in the corner, over there. The springs are sagging a bit, and the cushions are worn, but never mind. That armchair will do nicely.

Accelerated Human Evolution in past 40,000 years.

An interesting article by Nicholas Wade from the Dec. 11 NY Times:

Researchers analyzing variation in the human genome have concluded that human evolution accelerated enormously in the last 40,000 years under the force of natural selection.

The finding contradicts a widely held assumption that human evolution came to a halt 10,000 years ago or even 50,000 years ago. Some evolutionary psychologists, for example, assume that the mind has not evolved since the Ice Age ended 10,000 years ago.

But other experts expressed reservations about the new report, saying it is interesting but more work needs to be done.

The new survey — led by Robert K. Moyzis of the University of California, Irvine, and Henry C. Harpending of the University of Utah — developed a method of spotting human genes that have become more common through being favored by natural selection. They say that some 7 percent of human genes bear the signature of natural selection.

By dating the time that each of the genes came under selection, they have found that the rate of human evolution was fairly steady until about 50,000 years ago and then accelerated up until 10,000 years ago, they report in the current issue of The Proceedings of the National Academy of Sciences. The high rate of selection has probably continued to the present day, Dr. Moyzis said, but current data are not adequate to pick up recent selection.

Click on graphic to enlarge...

The brisk rate of human selection occurred for two reasons, Dr. Moyzis’ team says. One was that the population started to grow, first in Africa and then in the rest of the world after the first modern humans left Africa. The larger size of the population meant that there were more mutations for natural selection to work on. The second reason for the accelerated evolution was that the expanding human populations in Africa and Eurasia were encountering climates and diseases to which they had to adapt genetically. The extra mutations in their growing populations allowed them to do so.

Dr. Moyzis said it was widely assumed that once people developed culture, they protected themselves from the environment and from the forces of natural selection. But people also had to adapt to the environments that their culture created, and the new analysis shows that evolution continued even faster than before.

The researchers took their data from the HapMap project, a survey designed by the National Institutes of Health to look at sites of common variation in the human genome and to help identify the genes responsible for common diseases. The HapMap data, generated by analyzing the genomes of people from Africa, East Asia and Europe, has also been a trove for people studying human evolutionary history.

David Reich, a population geneticist at the Harvard Medical School, said the new report was “a very interesting and exciting hypothesis” but that the authors had not ruled out other explanations of the data. The power of their test for selected genes falls off in looking both at more ancient and more recent events, he said, so the overall picture might not be correct.

Similar reservations were expressed by Jonathan Pritchard, a population geneticist at the University of Chicago.

“My feeling is that they haven’t been cautious enough,” he said. “This paper will probably stimulate others to study this question.”

MindBlog freezes and thaws again

A holiday trip back to Madison Wisconsin, view from front door and back door of house on Twin Valley Road - just before the third time I had to shovel the walk... another 6 inches of snow since I left to return...

...back to Fort Lauderdale, view from front and back of condo on the South branch of the Middle River, 60-70 degree farenheit temperature increase:

Repressed Memory - A recent cultural invention?

Literary references to depression, hallucinations, anxiety, and dementia can be found throughout history. A fascinating article in Harvard Magazine by Ashley Pettus describes the research of Harrison Pope, who reasoned that if dissociative amnesia were an innate capability of the brain it also should appear in ancient texts. An extensive search, and a $1000 reward, was able to find no reference earlier than Nina, an opera by Dalayrac and Marsollier performed in Paris in 1786. The absence of dissociative amnesia in works prior to 1800 suggests that the phenomenon is not a natural neurological function, but rather a “culture-bound” syndrome rooted in the nineteenth century. From the article:

What, then, accounts for “repressed memory’s” appearance in the nineteenth century and its endurance today? Pope and his colleagues hope to answer these questions in the future. “Clearly the rise of Romanticism, at the end of the Enlightenment, created fertile soil for the idea that the mind could expunge a trauma from consciousness,” Pope says. He notes that other pseudo-neurological symptoms (such as the female “swoon”) emerged during this era, but faded relatively quickly. He suspects that two major factors helped solidify “repressed memory” in the twentieth-century imagination: psychoanalysis (with its theories of the unconscious) and Hollywood. “Film is a perfect medium for the idea of repressed memory,” he says. “Think of the ‘flashback,’ in which a whole childhood trauma is suddenly recalled. It’s an ideal dramatic device.”

Cognitive Recovery in Socially Deprived Young Children

With elaborate consideration of the ethical issues involved (commented on by Millum and Emanuel), Nelson et al. have compared the cognitive development of abandoned children reared in institutions to abandoned children placed in institutions but then moved to foster care (The Bucharest Early Intervention Project):

In a randomized controlled trial, we compared abandoned children reared in institutions to abandoned children placed in institutions but then moved to foster care. Young children living in institutions were randomly assigned to continued institutional care or to placement in foster care, and their cognitive development was tracked through 54 months of age. The cognitive outcome of children who remained in the institution was markedly below that of never-institutionalized children and children taken out of the institution and placed into foster care. The improved cognitive outcomes we observed at 42 and 54 months were most marked for the youngest children placed in foster care. These results point to the negative sequelae of early institutionalization, suggest a possible sensitive period in cognitive development, and underscore the advantages of family placements for young abandoned children.

Motion perception and production - similar neural coding

Another example of how our brain's representations of motion are tuned to biological actions. Here is the abstract of the open access article from Dayan et al., which contains some very elegant imaging figures:

Behavioral and modeling studies have established that curved and drawing human hand movements obey the 2/3 power law, which dictates a strong coupling between movement curvature and velocity. Human motion perception seems to reflect this constraint. The functional MRI study reported here demonstrates that the brain's response to this law of motion is much stronger and more widespread than to other types of motion. Compliance with this law is reflected in the activation of a large network of brain areas subserving motor production, visual motion processing, and action observation functions. Hence, these results strongly support the notion of similar neural coding for motion perception and production. These findings suggest that cortical motion representations are optimally tuned to the kinematic and geometrical invariants characterizing biological actions.

[Note: The 2/3 power law links path curvature C and angular velocity A along the movement by a power law with an exponent of 2/3. K is the velocity gain factor, which is piecewise constant during entire movement segments:
]

Monkeys and college students: similar in non-verbal math

This work from Cantlon and Brannon suggests that humans and nonhuman primates share a cognitive system for nonverbal arithmetic, suggesting an evolutionary link in their cognitive abilities., full text in PLoS Biology, here is the abstract:

Adult humans possess mathematical abilities that are unmatched by any other member of the animal kingdom. Yet, there is increasing evidence that the ability to enumerate sets of objects nonverbally is a capacity that humans share with other animal species. That is, like humans, nonhuman animals possess the ability to estimate and compare numerical values nonverbally. We asked whether humans and nonhuman animals also share a capacity for nonverbal arithmetic. We tested monkeys and college students on a nonverbal arithmetic task in which they had to add the numerical values of two sets of dots together and choose a stimulus from two options that reflected the arithmetic sum of the two sets. Our results indicate that monkeys perform approximate mental addition in a manner that is remarkably similar to the performance of the college students. These findings support the argument that humans and nonhuman primates share a cognitive system for nonverbal arithmetic, which likely reflects an evolutionary link in their cognitive abilities.

Human genetic variation - breakthrough of the year

We differ from each other in the number and order of our genes, and in their composition. A few edited clips from E. Pennisi's summary of Science Magazine's breakthrough of the year in the Dec. 21 issue:

There are an estimated 15 million places along our genomes where one base can differ from one person or population to the next. By mid-2007, more than 3 million such locations, known as single-nucleotide polymorphisms (SNPs), had been charted. Called the HapMap, this catalog has made the use of SNPs to track down genes involved in complex diseases--so-called genome-wide association studies--a reality....New gene associations now exist for type I and II diabetes, heart disease, breast cancer, restless leg syndrome, atrial fibrillation, glaucoma, amyotrophic lateral sclerosis, multiple sclerosis, rheumatoid arthritis, colorectal cancer, ankylosing spondylitis, and autoimmune diseases. One study even identified two genes in which particular variants can slow the onset of AIDS, demonstrating the potential of this approach for understanding why people vary in their susceptibility to infectious diseases.

Genomes can differ in many other ways. Bits of DNA ranging from a few to many thousands, even millions, of bases can get lost, added, or turned around in an individual's genome. Such revisions can change the number of copies of a gene or piece of regulatory DNA or jam two genes together, changing the genes'products or shutting them down. This year marked a tipping point, as researchers became aware that these changes, which can alter a genome in just a few generations, affect more bases than SNPs....In one study, geneticists discovered 3600 so-called copy number variants among 95 individuals studied. Quite a few overlapped genes, including some implicated in our individuality--blood type, smell, hearing, taste, and metabolism, for example. Individual genomes differed in size by as many as 9 million bases.

Learning from errors - genetic differences between humans

From Holden's brief summary of the work:

"Once burned, twice shy" works for most people. But some people are slow to learn from bad experiences.

This work shows that:

...people with a particular gene variant have more difficulty learning via negative reinforcement.
...demonstrates that a single-base-pair difference in the genome is associated with a remarkably different ability to learn from past mistakes is quite an accomplishment
...combines brain imaging with a task in which participants chose between symbols on a computer screen,
...centers on the A1 variant, or allele, of the gene encoding the D2 receptor, a protein on the surface of brain cells activated by the neurotransmitter dopamine. Earlier studies have hinted that this variant alters the brain's reward pathways and thereby makes people more vulnerable to addictions.

Brain activity was monitored (color) as a subject chose between two symbols (inset) and was rewarded with a smiley or frowny face. In the left panel the lower colors are hippocampus, the upper one the posterior medial frontal cortex.

Here is the abstract from Klein et al.

The role of dopamine in monitoring negative action outcomes and feedback-based learning was tested in a neuroimaging study in humans grouped according to the dopamine D2 receptor gene polymorphism DRD2-TAQ-IA. In a probabilistic learning task, A1-allele carriers with reduced dopamine D2 receptor densities learned to avoid actions with negative consequences less efficiently. Their posterior medial frontal cortex (pMFC), involved in feedback monitoring, responded less to negative feedback than others' did. Dynamically changing interactions between pMFC and hippocampus found to underlie feedback-based learning were reduced in A1-allele carriers. This demonstrates that learning from errors requires dopaminergic signaling. Dopamine D2 receptor reduction seems to decrease sensitivity to negative action consequences, which may explain an increased risk of developing addictive behaviors in A1-allele carriers.

Another difference in the brains of musicians...

Being a performing musician myself (cf. the YouTube video below), I'm always fascinated by work of the sort recently done by Chen et al. They show that musicians use the prefrontal cortex to a greater degree than nonmusicians to deconstruct and organize a rhythm's temporal structure. Here is their abstract (I will spare you the MRI images this time), followed by a bit of free music...

Much is known about the motor system and its role in simple movement execution. However, little is understood about the neural systems underlying auditory–motor integration in the context of musical rhythm, or the enhanced ability of musicians to execute precisely timed sequences. Using functional magnetic resonance imaging, we investigated how performance and neural activity were modulated as musicians and nonmusicians tapped in synchrony with progressively more complex and less metrically structured auditory rhythms. A functionally connected network was implicated in extracting higher-order features of a rhythm's temporal structure, with the dorsal premotor cortex mediating these auditory–motor interactions. In contrast to past studies, musicians recruited the prefrontal cortex to a greater degree than nonmusicians, whereas secondary motor regions were recruited to the same extent. We argue that the superior ability of musicians to deconstruct and organize a rhythm's temporal structure relates to the greater involvement of the prefrontal cortex mediating working memory.

Haydn Fantasia:

J. S. Bach - Christmas Oratorio - Schlafe, mein Liebster

John Eliot Gardiner leads the Monteverdi Choir and the English Baroque Soloists, with Bernarda Fink in "Schlafe, mein Liebster," from Bach's Christmas Oratorio (BWV 248).

Schlafe, mein Liebster, genieße der Ruh,
Wache nach diesem vor aller Gedeihen!
Labe die Brust,
Empfinde die Lust,
Wo wir unser Herz erfreuen!

Sleep now, my dearest, enjoy now thy rest,
Wake on the morrow to flourish in splendor!
Lighten thy breast,
With joy be thou blest,
Where we hold our heart's great pleasure!

Neural correlates of trust

Krueger et al. offer an MRI study of brain changes that occur during a reciprocal trust game. They:

.used hyperfunctional magnetic resonance imaging, in which two strangers interacted online with one another in a sequential reciprocal trust game while their brains were simultaneously scanned. By designing a nonanonymous, alternating multiround game, trust became bidirectional, and we were able to quantify partnership building and maintenance...We show that the paracingulate cortex is critically involved in building a trust relationship by inferring another person's intentions to predict subsequent behavior. This more recently evolved brain region can be differently engaged to interact with more primitive neural systems in maintaining conditional and unconditional trust in a partnership. Conditional trust selectively activated the ventral tegmental area, a region linked to the evaluation of expected and realized reward, whereas unconditional trust selectively activated the septal area, a region linked to social attachment behavior. The interplay of these neural systems supports reciprocal exchange that operates beyond the immediate spheres of kinship, one of the distinguishing features of the human species.

Figure - Brain responses for decisions to trust. (a) Trust building. Decisions to trust contrasted with the control condition activated the PcC (Brodmann's areas, BA 9/32). (b) Trust maintenance. Decisions to trust contrasted with the control condition activated the SA (together with the adjoining hypothalamus)

Laws of Nature as resting on faith...

Dennis Overbye does a brief piece in the Dec. 18 NY Times that derives from the small firestorm of commentary ignited by a previous OpEd piece by Paul Davis, an Arizona State Univ. cosmologist, asserting that science, not unlike religion, rests on faith, not in God but in the idea of an orderly universe. (I almost did a post on that OpEd article, but decided not to). The not so minor difference, of course, is that the "laws" of science simply reflect that the order we perceive in nature has been explored and tested for more than 2,000 years by observation and experimentation. The methods of science are well known. What are the methods of faith? Overbye's article proceeds to describe positions held by a number of prominent philosophers, physicists, and cosmologists on the underlying nature of the universe.

I'm with the late Nobel laureate physicist Richard Feynman, whose famous quote is included in the article - “Philosophy of science is about as useful to scientists as ornithology is to birds.”

Children attributing causality - extension to religious and political imitation.

Blog reader Rick Thomas makes a brief comment on the previous post on children attributing causality (a comment I wish I had made), that is sufficiently pungent to bring into a post where more people will note it:

" Fascinating. I guess the effect will extend to adult religious and political imitation as well."

Even though the experiments of Lyons et al. mentioned in the previous post deal with imitation of mechanical sequences, the same tenacious and irrational attribution of causality might explain why people find it so difficult to overcome habits instilled by their early religious and political environment.

The hidden structure of over-imitation

Human children, unlike chimpanzees, will copy unnecessary or arbitrary parts of an action sequence they observe in adults, Lyons et al. term this process overimitation and suggest in an open access article with the title of this post that it reveals a hidden structure behind how children learn to attribute causality. Here is their abstract, and a graphic showing one of the three puzzle boxes used in the experiements:

Young children are surprisingly judicious imitators, but there are also times when their reproduction of others' actions appears strikingly illogical. For example, children who observe an adult inefficiently operating a novel object frequently engage in what we term overimitation, persistently reproducing the adult's unnecessary actions. Although children readily overimitate irrelevant actions that even chimpanzees ignore, this curious effect has previously attracted little interest; it has been assumed that children overimitate not for theoretically significant reasons, but rather as a purely social exercise. In this paper, however, we challenge this view, presenting evidence that overimitation reflects a more fundamental cognitive process. We show that children who observe an adult intentionally manipulating a novel object have a strong tendency to encode all of the adult's actions as causally meaningful, implicitly revising their causal understanding of the object accordingly. This automatic causal encoding process allows children to rapidly calibrate their causal beliefs about even the most opaque physical systems, but it also carries a cost. When some of the adult's purposeful actions are unnecessary—even transparently so—children are highly prone to mis-encoding them as causally significant. The resulting distortions in children's causal beliefs are the true cause of overimitation, a fact that makes the effect remarkably resistant to extinction. Despite countervailing task demands, time pressure, and even direct warnings, children are frequently unable to avoid reproducing the adult's irrelevant actions because they have already incorporated them into their representation of the target object's causal structure.

Vegansexuality

Jeff Stryker gives us more from the fringe (Dec. 9 NY Times Magazine):

Forget homo-, bi- or even metro-: the latest prefix in sexuality is vegan-, as in “vegansexual.” In a study released in May, Annie Potts, a researcher at the University of Canterbury and a director of the New Zealand Centre for Human-Animal Studies, surveyed 157 vegans and vegetarians (120 of them women) on the topic of cruelty-free living. The questions ranged from attitudes about eating meat to keeping pets to wearing possum fur to, yes, “cruelty-free sex” — that is, “rejecting meat eaters as intimate partners.”

Some of the survey respondents volunteered their reluctance to kiss meat eaters. “I couldn’t think of kissing lips that allow dead animal pieces to pass between them,” a 49-year-old vegan woman from Auckland said. For some, the resistance is the squeamishness factor. “Nonvegetarian bodies smell different to me,” a 41-year-old Christchurch vegan woman said. “They are, after all, literally sustained through carcasses — the murdered flesh of others.” For some, it is a question of finding a like-minded life partner. An Auckland ovo-vegetarian had tried a relationship with a carnivore, but reported that despite the sexual attraction, the gulf in “shared values and moral codes” was just too wide.

Potts, who coined the term vegansexuality, says the “negative response of omnivores” to her study has surprised her. Even some fellow animal lovers question the wisdom of vegansexuality. A blog for People for the Ethical Treatment of Animals noted that sleeping with only fellow vegans means forgoing the opportunity to turn carnivores into vegans by the most powerful recruiting tool available — sex.

PETA’s founder and president, Ingrid Newkirk, agrees that vegans smell fresher. (“There’s science to prove it,” she says.) But Newkirk is all about the recruiting, even if it means one convert at a time. “When my staff members come to me and say: ‘Guess what? My boyfriend, now he’s a vegan,’ I say, half-jokingly: ‘Well, it is time to ditch him and get another. You’ve done your work; move on.’ ”