Sniffing women’s' tears reduces aggression in men.
Research by Israeli scientists has shown that sniffing tears can reduce male aggression by almost 44% by lowering the level of testosterone.
The problem for Christianity here is that the entire rationale for the religion is that human free will allowed the mythical founder couple, who were magically created without ancestors, to choose to disobey their magic creator in the so-called 'Fall'.
Because the magic, omnipotent creator has never managed to get over this exercise of the free will it gave them, we need Jesus (the magic creator personified) to help him forgive us, because he had himself sacrificed in a blood sacrifice that everyone knows satiates irascible gods, especially when it's them being sacrificed. (I'm not making this up! Just ask any Christian who Jesus was and what he was born for.)
But, if behaviour is mediated by physiology in the form of hormones and if the levels of those hormones can be mediated by external influences, then external influences can modify behaviour, so where does that leave the notion of free will?
Obviously, the authors of that tale in the Bible knew nothing of hormones and pheromones and how they can modify and influence behaviour.
The research is explained in a press release from the American Committee for the Weizmann Institute of Science:
All land mammals have tear glands in their eyes, but, until recently, the human tearing experience was considered unique. After all, humans are the only animals to shed tears while watching Beaches. Now a new Weizmann Institute of Science study reveals that human tears have much more in common with those of other animals than previously thought: Just as with the tears of mice and blind mole rats, they contain chemicals that reduce aggression in others. The study, published today in PLOS Biology, showed that sniffing women’s tears lowered brain activity related to aggression in men, reducing aggressive behavior.For technical details we can turn to the open access paper on PLOS Biology:
The study addressed the long-standing mystery of why we cry. Charles Darwin was puzzled by emotional tearing, which appeared to have no useful function – beyond the role that tears play in lubricating the eye – so he concluded that such tearing must have evolved in humans by chance. However, numerous studies since then, particularly in rodents, have shown that mammalian tears contain chemicals serving as social signals that can be emitted on demand.
One of the most common purposes of these tears is to reduce aggression. The tear liquid of female mice contains chemicals that affect aggression networks in the brain, thereby reducing fighting among male mice. Similarly, subordinate male blind mole rats smear themselves in tears to reduce the aggressive behavior they face from dominant males.
Prof. Noam Sobel, whose lab in Weizmann’s Brain Sciences Department studies olfaction, the sense of smell, has hypothesized that human tears also contain chemicals that serve as social signals. In 2011, his team showed in research published in Science that sniffing women’s emotional tears reduced testosterone levels in men, resulting in somewhat diminished levels of sexual arousal.
In the new study, researchers, led by PhD student Shani Agron from Sobel’s lab, set out to determine whether tears have the same aggression-blocking effect in people as they do in rodents. In a series of experiments, men were exposed to either women’s emotional tears or saline, without knowing what they were sniffing or being able to distinguish between the two. Next, they played a two-person game designed to elicit aggressive behavior in one player toward the other, who was portrayed to be cheating. When given the opportunity, the men could get revenge on the perceived cheaters by causing them to lose money, though they themselves gained nothing. After the men sniffed women’s emotional tears, their revenge-seeking aggressive behavior during the game dropped by about 44% – or nearly in half.
This seemed equivalent to the effect observed in rodents, but rodents have a structure in their noses called the vomeronasal organ that picks up social chemical signals. Since humans don’t have this organ, researchers wanted to know how they were able to sense the social chemicals. To find an answer, the researchers applied the tears to 62 human olfactory receptors in a laboratory dish and found that four of these receptors were activated by the tears, even though tears are odorless.
The researchers repeated the experiments while examining the men’s brains in an MRI scanner. Functional imaging showed that two aggression-related brain regions – the prefrontal cortex and the anterior insula – were less active when the men were sniffing the tears. The greater the difference in this brain activity between saline and tears, the less often the player took revenge during the game.
We’ve shown that tears activate olfactory receptors and that they alter aggression-related brain circuits, significantly reducing aggressive behavior,” Sobel says. “These findings suggest that tears are a chemical blanket offering protection against aggression – and that this effect is common to rodents and humans, and perhaps to other mammals as well.
Professor Noam Sobel, senior author.
The Azrieli National Center for Human Brain Imaging and Research
Weizmann Institute of Science
Rehovot, Israel.
In fact, recent studies have found that dogs also shed emotional tears. However, more research is needed to determine whether these tears contain chemical signals that can be picked up by other dogs or by humans.
As for social interactions among humans, future research will explore whether the new study’s findings also apply to women. “When we looked for volunteers who could donate tears, we found mostly women, because for them it’s much more socially acceptable to cry,” Agron says. “We knew that sniffing tears lowers testosterone, and that lowering testosterone has a greater effect on aggression in men than in women, so we began by studying the impact of tears on men because this gave us higher chances of seeing an effect. Now, however, we must extend this research to include women to obtain a fuller picture of this impact.”
Agron adds that this effect is likely to gain in importance when verbal communication is impossible, as with babies: “Infants can’t talk, so for them relying on chemical signals to protect themselves against aggression can be critical.”
AbstractThese results are compelling evidence that tears in women and children can reduce aggression in males, in humans and other mammals. It is easy to see how this evolved, especially when the male sex hormone can promote aggression which can be an advantage when competing for females, but which can be dangerous when directed at women and children.
Rodent tears contain social chemosignals with diverse effects, including blocking male aggression. Human tears also contain a chemosignal that lowers male testosterone, but its behavioral significance was unclear. Because reduced testosterone is associated with reduced aggression, we tested the hypothesis that human tears act like rodent tears to block male aggression. Using a standard behavioral paradigm, we found that sniffing emotional tears with no odor percept reduced human male aggression by 43.7%. To probe the peripheral brain substrates of this effect, we applied tears to 62 human olfactory receptors in vitro. We identified 4 receptors that responded in a dose-dependent manner to this stimulus. Finally, to probe the central brain substrates of this effect, we repeated the experiment concurrent with functional brain imaging. We found that sniffing tears increased functional connectivity between the neural substrates of olfaction and aggression, reducing overall levels of neural activity in the latter. Taken together, our results imply that like in rodents, a human tear–bound chemosignal lowers male aggression, a mechanism that likely relies on the structural and functional overlap in the brain substrates of olfaction and aggression. We suggest that tears are a mammalian-wide mechanism that provides a chemical blanket protecting against aggression.
Introduction
Mammals use various bodily media to convey social chemical signals. For example, human social chemosignaling research has focused on sweat [1], and rodent research has focused on urine [2]. Social chemosignaling, however, also extends to media such as feces [3], milk [4], and tears [5–12]. Rodent tear signaling has been studied in 2 contexts: reproduction and aggression. In reproduction, a male-specific peptide secreted from the extraorbital lacrimal gland, named exocrine gland-secreting peptide 1 (ESP1), is transduced by female V2Rp5-expressing vomeronasal sensory neurons [5]. This triggers signals from the accessory olfactory bulb to hypothalamic and amygdaloid nuclei, which enhance female sexual receptive behavior [6]. The tear-bound signal ESP1 is also the primary signal in the Bruce effect, where a pregnant mouse will miscarry upon perceiving an ESP1 signal from a male who did not father the pregnancy [7]. These tear-bound signals function not only within species but also across species: Like ESP1 in mice, rat cystatin-related protein 1 (ratCRP1) is released from male rat tears and alters behavior in female rats. This same rat signal, however, also triggers predator avoidance in mice [9]. Beyond reproductive signaling, a primary domain for rodent tear signaling is aggression. The above noted tear signal ESP1 that promotes sexual behavior in females also increases aggressive behavior in males smelling their own ESP1 secretions [8]. However, most aggression-related tear signaling appears to block rather than promote aggression. This was first identified in blind mole rats, where subordinate males cover themselves in tears to reduce dominant male aggression toward them [10]. Similarly, mice pups emit in their tears exocrine gland-secreting peptide 22, which through a vomeronasal accessory olfactory pathway, reduces male sexual aggression toward them [11]. Finally, female mouse tear liquid contains signals that abolish intermale aggression by modulation of activity in aggression brain networks [12]. In contrast to this extensive body of research into rodent tear chemosignaling, there is only limited evidence for human tear chemosignaling. Human female tears contain a perceptually odorless chemical signal that when sniffed, lowers testosterone in human males [13,14], but the behavioral significance of this effect remains poorly understood. More specifically, one study found that sniffing tears drove a small but significant reduction in ratings of sexual arousal attributed to pictures [13], and the second study observed that despite significantly lowering testosterone, sniffing tears did not affect appetite [14]. Given that reduced male testosterone is associated with reduced male aggression [15], here, we set out to test the hypothesis that like in rodents, human tears contain a chemical signal that blocks aggression. Notably, there are indeed several instances of chemical signals altering hormonal-dependent behavior in humans [16]. Examples include maternal behavior [17,18], ingestive behavior [19,20], social behavior in general [21,22], and sociosexual behavior in particular [23–25]. In other words, that a chemical signal can alter human behavior is not unusual. Moreover, particularly emotional behaviors are a prime candidate for modulation by chemical signals [26], possibly a reflection of their shared neural substrates in the amygdaloid complex [27,28] and an extensive associated brain network spanning ventral temporal cortex, frontal cortex, anterior cingulate cortex, and insula striatum [29]. Given this neural link, and that human aggression can be measured behaviorally using various standardized tasks [30], we set out to measure the aggressive behavioral and brain response following sniffing emotional tears.
Fig 1. Tears did not perceptually differ from saline. Scatter plots of the normalized VAS ratings of tears and trickled saline for (A) pleasantness, (B) intensity, and (C) familiarity. Each dot is the average of 10 sniffs by a given participant; light-colored dots are from Experiment 1 (n = 22), and dark dots are from Experiment 3 (n = 24). The data in (A-C) are presented along a unit slope line (X = Y), such that if points accumulate above the line, this implies higher values after tears; if points accumulate below the line, this implies higher values after saline; and if points are distributed around the line, this implies no difference. Data used to generate graphs can be found in S1 Data.
Fig 2. Sniffing emotional tears blocks male aggression. (A) Aggression ratings (APR) in Experiment 1, obtained after exposure to tears or saline. Each dot is a participant, n = 25. (B) The same data as in (A), presented in violin-plot. Each dot is a participant. The white dot represents the median, and the gray bar represents the quartiles. Saline in red and tears in blue. (C) Bootstrap analysis. Gray lines represent the 10,000 repetitions; the blue line represents the actual APR difference between saline and tears. (D) Scatter plots of the aggression ratings (APR) obtained in the MRI (Experiment 3) after exposure to tears or saline. Each dot is a participant, n = 26. (E) The same data as in (A) presented in violin-plot. Saline in red and tears in blue. The data in (A) and (D) are presented along a unit slope line (X = Y), such that if points accumulate above the line, this implies higher values after tears; if points accumulate below the line, this implies higher values after saline; and if points are distributed around the line, this implies no difference. Data used to generate graphs can be found in S1 Data.
Fig 3. Perceptually odorless emotional tears activated human olfactory receptors in vitro.
The normalized luminescence from the OR response to tears or trickled saline, ranging in concentration from 1% to 3.16% (in CD293 simulation medium). A dose response to tears but not trickled saline was evident in receptors (A) OR11H6, (B) OR2AG2, (C) OR5A1, and (D) OR2J2. (E) No dose response was seen in the control empty vector—pCI. Each dot is the mean of 3 repetitions for either tears (blue) or saline (red), and the error bar is the standard error across 3 replications. A two-way ANOVA followed by a Sidàk’s multiple comparison test was performed at each concentration between the OR response to tears and saline (*** = p < 0.0001, ** = p < 0.001, * = p < 0.05, no symbol = not significantly different). Data used to generate graphs can be found in S3 Data.
Fig 4. Tears reduced activation in the brain substrates of reactive aggression.
(A) Statistical map of the GLM ANOVA Provocation > inactive time contrast with an added level of saline vs. tears (tears < saline in blue; tears > saline in red), n = 24. GLM z threshold > 2.58, cluster corrected to p = 0.05. Color bars represent z-values. (B, C) Correlation between differences in behavioral APR scores (saline -tears) and differences in beta values (saline- tears) of (B) left AIC and (C) PFC. Each dot represents a participant, n = 24. The continuous line represents the fit. The dashed line marks the confidence bounds. Spearman rank correlation coefficient and p-values are depicted. Data used to generate graphs can be found in S1 Data; fMRI data are available at https://openneuro.org/datasets/ds004274.
Fig 5. Tears coordinate the brain response in aggression.
(A) Functional connectivity statistical parametric map during provocation > inactive time with an added level of saline vs. tears. Tears < saline in blue. Tears > saline in hot colors. Color bars represent z-values, n = 24. (B, C) Scatter plots of tears vs. saline present the beta values of functional connectivity between left AIC and (B) right TP and (C) right amygdala. Each dot represents a subject, n = 24. The data are presented along a unit slope line (X = Y), such that if points accumulate above the line, this implies higher beta values for tears; if points accumulate below the line, this implies higher beta values for saline; and if points are distributed around the line, this implies no difference. (D) Spearman rank correlation between the difference in APR scores in tears vs. saline and increase in connectivity between the left AIC and right amygdala under tears. Each dot represents a participant, n = 24. The continuous line represents the fit. The dashed line marks the confidence bounds. Spearman rank correlation coefficient and p-value are depicted. Data used to generate graphs can be found in S1 Data; fMRI data are available at https://openneuro.org/datasets/ds004274.
Agron S, de March CA, Weissgross R, Mishor E, Gorodisky L, Weiss T, et al. (2023)
A chemical signal in human female tears lowers aggression in males. PLoS Biol 21(12): e3002442. https://doi.org/10.1371/journal.pbio.3002442
Copyright: © 2023 The authors.
Published by PLoS. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Evolution has produced a hormone which is useful in some situations but needs controlling in others, and tears, or rather the pheromone in them, is the means by which this is achieved. It makes sense as the result of a mindless evolutionary process but not as the result of intelligent design by a designer who should have anticipated the problem testosterone would cause. Instead, we have the result of an evolutionary arms race between males and the children and females, which seems to have reached a state of equilibrium.
But it is the notion of free will and the implications that has for the rationale of Christianity that this research calls into question. Behaviour which can be modified by external factors is not behaviour under the control of free will; it is behaviour under the control of chemicals.
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