Saturday, February 25, 2023

The human appetite for recreational drugs could be a heritage of the Stone Age switch to a meat-based diet and the need to protect an ever-expanding brain from zoonotic infections

Homo medicus: The transition to meat eating increased pathogen pressure and the use of pharmacological plants in Homo. Edward H. Hagen, Aaron D. Blackwell, Aaron D. Lightner, Roger J. Sullivan. American Journal of Biological Anthropology, February 23 2023.

Abstract: The human lineage transitioned to a more carnivorous niche 2.6 mya and evolved a large body size and slower life history, which likely increased zoonotic pathogen pressure. Evidence for this increase includes increased zoonotic infections in modern hunter-gatherers and bushmeat hunters, exceptionally low stomach pH compared to other primates, and divergence in immune-related genes. These all point to change, and probably intensification, in the infectious disease environment of Homo compared to earlier hominins and other apes. At the same time, the brain, an organ in which immune responses are constrained, began to triple in size. We propose that the combination of increased zoonotic pathogen pressure and the challenges of defending a large brain and body from pathogens in a long-lived mammal, selected for intensification of the plant-based self-medication strategies already in place in apes and other primates. In support, there is evidence of medicinal plant use by hominins in the middle Paleolithic, and all cultures today have sophisticated, plant-based medical systems, add spices to food, and regularly consume psychoactive plant substances that are harmful to helminths and other pathogens. We propose that the computational challenges of discovering effective plant-based treatments, the consequent ability to consume more energy-rich animal foods, and the reduced reliance on energetically-costly immune responses helped select for increased cognitive abilities and unique exchange relationships in Homo. In the story of human evolution, which has long emphasized hunting skills, medical skills had an equal role to play.


The final category of pharmacological plant use that requires an evolutionary explanation is the widespread, habitual use of “recreational” drugs like caffeine, nicotine, and THC, which we also conceptualize as (mostly) a constitutive defense. Previously, two of the authors (EHH and RJS) and their colleagues proposed that use of these substances might have evolved as constitutive and inducible defenses against pathogens (Hagen et al., 2009; Hagen et al., 2013; Roulette et al., 2014; Sullivan et al., 2008). Here we extend this hypothesis to the behavioral defense of the CNS specifically, which tripled in size in the Pleistocene and might have been subject to increased virulent infections, as described earlier. This extension is based on the substantial differences in immune defenses of the brain vs. other tissues and organs.

Most tissues have mechanisms to restore functionality when damaged or infected, which typically involves the destruction and removal of injured or infected cells (D'Arcy, 2019; Deretic et al., 2013), and the generation of new cells (Clevers & Watt, 2018; Xia et al., 2018). Herpes simplex virus infection of skin cells, for example, results in massive immune- and virus-mediated cell death, followed by rapid replacement of the cells. Most human neurons, however, cannot be replaced in adulthood because loss of neurons entails the loss of functionality and often irreplaceable information, such as in Alzheimer's disease where neuronal cell death causes permanent loss of memory and other cognitive dysfunctions (Arendt et al., 2015). Although adult neurogenesis has been reported in a wide range of vertebrates, including birds, rodents, and primates, in humans it is very limited and perhaps non-existent (Denoth-Lippuner & Jessberger, 2021; Franjic et al., 2022; Gage, 2019; Lucassen et al., 2020; Moreno-Jiménez et al., 2019; Oppenheim, 2019; Sorrells et al., 2018). The unique value of neurons presents a conundrum to the immune system: how to defend the brain from pathogens if destroying infected neurons would cause permanent loss of critical learned information or other functionality (Miller et al., 2016; Solomos & Rall, 2016)? Moreover, CNS inflammatory responses interfere with CNS functions, sometimes permanently, even without neuronal death (Klein et al., 2017). Constitutive defenses are one solution (Paludan et al., 2021).

8.1 The blood-brain barrier, a constitutive defense

The brain is defended by a physical blood brain barrier (BBB). The BBB prevents most blood-borne pathogens from infecting the brain. It also prevents most plant toxins and other xenobiotics from entering the brain (Banks, 2016; Iadecola, 2017; Villabona-Rueda et al., 2019), including most pharmaceuticals, which often chemically resemble plant toxins (Agúndez et al., 2014). These properties pose a considerable challenge to drug treatment of pathogens that do manage to infect the CNS (Pardridge, 2012; Terstappen et al., 2021). Certain small molecules can cross the BBB via lipid-mediated free diffusion, however, including widely used “recreational drugs” like nicotine and caffeine.

8.2 CNS immune privilege and defense

For much of the last century, knowledge that the BBB prevented most pathogens from reaching the CNS and that tissue grafts implanted in the CNS parenchyma (functional tissue) did not provoke rejection, supported the view that the CNS was an “immune privileged” site. Recent discoveries that the brain parenchyma is connected to the peripheral immune system via meningeal lymphatic vessels have stimulated debate over the nature of immunity in the brain.

One mainstream view is that barriers establish compartments in the CNS that differ functionally in their access to the immune system and some are immune privileged and others are not (Engelhardt et al., 2017). The meninges surrounding the CNS parenchyma, for instance, contain a wide repertoire of immune cells, including monocytes and B cells from special skull and vertebral bone marrow reservoirs, that provide immune surveillance of the CNS (Alves de Lima et al., 2020; Brioschi et al., 2021; Cugurra et al., 2021). Although the CNS parenchyma can mount an inflammatory response to infection via resident microglia (brain-specific macrophages) and other cells, as well as cells migrating from the meninges, it is characterized by a dearth of adaptive and innate immune responses relative to peripheral tissues (Engelhardt et al., 2017).

Immune privilege is a double-edged sword, however. Despite formidable CNS defenses such as the BBB, pathogens do manage to infect the CNS. The protection immune privilege provides to neurons also creates a niche in which pathogens that manage to infect the CNS can evade destruction by the immune system (Cain et al., 2019; Forrester et al., 2018). In fact, to maintain neuronal integrity, immune responses in the CNS might favor controlling pathogens rather than eliminating them (Matta et al., 2021; Miller et al., 2016).

8.3 Habitual recreational drug use as a constitutive pathogen defense

Humans have evolved to be exceptionally reliant on learned information and other CNS functions across a lifespan that exceeds that of most other mammals, and they occupied a dietary niche with high exposure to potentially zoonotic pathogens, including those that infect the CNS. Yet immune defense of the CNS is constrained. Chemoprophylaxis and chemotherapy with compounds that are harmful to CNS pathogens but well-tolerated by the CNS would complement the immune system. Such an evolved chemoprotective strategy for the CNS requires antipathogenic compounds that can cross the BBB.

Most common recreational drugs, including caffeine, nicotine, THC, and arecoline in betel nut, are plant defensive neurotoxins (ethanol, a yeast fermentation product, is the major exception). Sullivan, Hagen, and colleagues argued that the prevailing evolutionary “hijack hypothesis” of recreational drug use, in which evolutionarily novel substances incidentally activate dopamine reward circuits (Kelley & Berridge, 2002; Wise, 1998), was implausible because similar compounds have been part of primate diets for millions of years (Hagen et al., 2009; Hagen et al., 2013; Sullivan et al., 2008; Sullivan & Hagen, 2002).

Psychoactive substance seeking might instead be an evolved self-medication strategy to defend against intestinal helminths and other pathogens (Hagen et al., 2009; Hagen et al., 2013; Sullivan et al., 2008; Sullivan & Hagen, 2002). All globally popular recreational drugs are toxic to helminths, as are some hallucinogenic plants used by Amazonian peoples (Rodríguez et al., 1982); nicotine was widely used to deworm livestock prior to the development of modern anthelmintics, and has the same mechanism of action as some commercial anthelmintics; an aqueous solution of tobacco is still used to deworm livestock in some low-income settings (efficacy quantitatively verified); tobacco is widely mentioned as an anthelmintic in ethnomedical texts; treatment of intestinal helminths in hunter-gatherers transiently reduces tobacco use, and tobacco and cannabis use is negatively associated with worm burden and reinfection; and there is a switch-like transition by virtually all humans to regular use of one or more of these pharmacologically potent substances in adolescence once teratogenic risks to the developing brain have dropped (Hagen et al., 2009; Hagen & Sullivan, 2018; Roulette et al., 2014; Roulette, Kazanji, et al., 2016; Sullivan et al., 2008; Sullivan & Hagen, 2002). In this model, females avoid culturally identified teratogenic substances such as tobacco during pregnancy and their reproductive years, increasing use postmenopause (Hagen et al., 20162013; Hagen & Tushingham, 2019; Placek et al., 2017). See Figures 7 and 8.


(a–d) The universal transition to psychoactive druge use in adolescence. Cumulative distribution of self-reported age of first use of alcohol, tobacco, cannabis, and cocaine in a large (N = 85,052) cross-national sample of users of these substances. Figure from Degenhardt et al. (2016). (e) Prevalence of tobacco and cannabis use among Aka forager children, adolescents, and adults, by sex (no children reported use). Data from Roulette, Hagen, et al. (2016). (f) Urinary caffeine metabolite (AAMU: 5-acetylamino-6-amino-3-methyluracil) excretion rate in a nationally representative US sample (N = 2714); 97.5% had detectable AAMU. Self-reported caffeine intake in this sample exhibited the same age dependence, as did concentrations of urinary caffeine and other caffeine metabolites. Figure and data from Rybak et al. (2015). These patterns suggest the existence of a developmental “switch” to psychoactive drug use during adolescence.


Theoretical model of recreational drug use as an evolved constitutive pathogen defense that varies by age, sex, reproductive status, total fertility rate (TFR), and cultural information about teratogenic substances. For details, see Hagen et al. (2016) and Hagen and Tushingham (2019).

Helminths are an important class of CNS parasites, and of course all recreational drugs cross the BBB. Here we extend the antiparasite hypothesis of recreational drug use to pathogens that infect the CNS, focusing on the helminth T. solium as a key example. Humans, dogs, and other animals infected with Taenia and other tapeworm species have often been treated with arecoline hydrobromide (Gemmell, 1958; Li et al., 2012). Arecoline is an agonist of muscarinic acetylcholine receptors, which have numerous roles including in neuromuscular junctions. Arecoline's mechanism of action against cestodes is probably to induce paralysis (Liu et al., 2016). Arecoline readily crosses the BBB and is the primary psychoactive alkaloid in the seed of Areca catechu palm, which is typically chewed with the leaf of the Piper betle and slaked lime, a concoction termed betel quid or paan (Volgin et al., 2019). Betel quid is widely consumed in Asia and the Pacific and is probably the fourth most widely used psychoactive substance after caffeine, alcohol, and tobacco (Arora & Squier, 2019; Gupta & Warnakulasuriya, 2002; Mehrtash et al., 2017). Areca seeds, often combined with pumpkin seeds, were one of several frequently mentioned treatments of Taenia infections in Chinese medical texts dating back about 2000 years (Zou & Ye, 2014). In a controlled study in humans this combination was found to be close to 90% effective at expelling Taenia tapeworms (Li et al., 2012). Whether arecoline also kills Taenia larvae in the brain is unknown, and killing larvae in the brain induces inflammation, potentially creating more problems than it solves. However, most of the medical community has accepted that the benefits of antiparasitic treatment of neurocysticercosis outweigh the risks (García et al., 2003). In an observational study of individuals suffering epileptic seizures, many of whom probably had neurocysticercosis based on the local prevalence of this disease, chewers of Areca catechu (1/3 of the sample) had 59% fewer seizures in the month prior, compared to non-chewers (a mean of 1.4 vs. 3.3 seizures, respectively, Mateen et al., 2017).

It is intriguing that a tapeworm that humans acquired from carnivores in the Pleistocene, and which infects the CNS and other tissues, is potentially treatable with the active compound in one of the world's most popular “recreational” drugs, used on a daily basis by a sizable fraction of the world's population, and that among those with seizures, use of the drug is negatively associated with seizure frequency. It is also intriguing that caffeine, the world's most popular drug, inhibits growth of T. gondii (Munera López et al., 2019), another common neurotropic pathogen. Consumption of ethanol, like consumption of pharmacological plant substances, could also be a self-medication strategy: it is a potent antimicrobial compound, and there is evidence that it mitigates infections of H. pylori in vitro and in vivo (Liu et al., 2016; Xia et al., 2020).

Extending previous work (Hagen et al., 2009; Hagen et al., 2013; Sullivan et al., 2008), we propose that when the benefits exceed the costs, humans, and perhaps other animals, have an evolved propensity to seek out and regularly consume psychoactive plant defensive chemicals, that is, those that cross the BBB and interfere with neural signaling, so as to deter, control, and eliminate pathogen invasions of the immune privileged CNS parenchyma.

So-called "positive psychology" has a negative track record in scientific soudness

The critiques and criticisms of positive psychology: A systematic review. Llewellyn E. van Zyl et al. The Journal of Positive Psychology, Feb 23 2023.

Abstract: The purpose of this systematic literature review was to explore the current critiques and criticisms of positive psychology and to provide a consolidated view of the main challenges facing the third wave of research. The review identified 32 records that posed 117 unique criticisms and critiques of various areas of the discipline. These could be grouped into 21 categories through conventional content analysis, culminating in six overarching themes or ‘broad criticisms/critiques’. The findings suggested that positive psychology (a) lacked proper theorizing and conceptual thinking, (b) was problematic as far as measurement and methodologies were concerned, (c) was seen as a pseudoscience that lacked evidence and had poor replication, (d) lacked novelty and self-isolated itself from mainstream psychology, (e) was a decontextualized neoliberalist ideology that caused harm, and (f) was a capitalistic venture. We briefly reflect on the findings and highlight the opportunities these criticisms and critiques present.

Keywords: Criticisms of positive psychologycritiqueschallengesopportunitiespositive psychologyThird Wave Positive Psychology

Discussion and future directions

This systematic literature review aimed to explore the contemporary critiques and criticisms posed of the discipline and to provide a consolidated view of the main challenges facing the third wave of positive psychology. The review identified 32 records that posed 117 unique criticisms and critiques of various areas of the discipline. These could be grouped into 21 categories through conventional content analysis, culminating in six overarching themes or ‘broad criticisms/critiques’. The findings discussed in the previous section suggested that positive psychology (a) lacked proper theorizing and conceptual thinking, (b) was problematic as far as measurement and methodologies were concerned, (c) was seen as a pseudoscience that lacked evidence and had poor replication, (d) lacked novelty and self-isolated from mainstream psychology, (e) was a decontextualized neo-liberalist ideology that caused harm, and (f) was a capitalistic venture (cf., Figure 2). We briefly reflect on the findings and highlight future directions in the discussion below.

Getting to the root(s) of the problem: improper theorizing and poor measurement/methods

Although the relative importance of the six broad criticisms/critiques was difficult to determine, each of the 32 records highlighted problems relating to improper theorizing and conceptual thinking within positive psychology and issues with its measurement and (research) methodologies. It can be argued that these two issues are the proverbial root cause of problems in positive psychology.

Our first finding showed that most critics believed that positive psychology lacked proper theorizing and conceptual thinking. According to them, positive psychology lacked a unified metatheory that grounded the philosophy underpinning the science and failed to provide a clear set of ideas or criteria regarding how positive psychological phenomena had to be conceptualized, examined, and approached. These criticisms and the limitations to theory development are neither new nor neglected by positive psychologists (Van Zyl & Rothmann, Citation2022; Wissing, Citation2021). Positive psychological scientists have had widespread debates on the epistemological, ontological, and axiological beliefs driving the discipline (cf., Diener, Citation2012; Lomas & Ivtzan, Citation2016; M. Seligman, Citation2018; Waterman, Citation2013; Wissing, Citation2021). These philosophical debates have aimed to create widespread consensus on the world views of positive psychology to determine the most appropriate methods, terminologies, and types of theories required to move the discipline forward (cf., Wissing, Citation2021). Over time, these philosophical debates about the view of positive psychology of human nature and the real world (ontology), beliefs regarding how knowledge is generated/validated (epistemology), and views of what it values or what is considered desirable/undesirable (axiology) have become more ‘tangible’ (Wissing, Citation2021). Recently, Ciarrochi et al. (Citation2022), Wissing (Citation2021), Lomas et al. (Citation2021), and M. Seligman (Citation2018), and others started to clarify the philosophical position of positive psychology, presented clearer guidelines for theory development, highlighted the methods/approaches required to advance the field, and set guidelines on how to address paradigmatic issues.

For example, Seligman’s (Citation2011, p. 13) PERMA framework of well-being (Positive emotions, Engagement, positive Relationships, Meaning, and Accomplishments) received widespread criticism from scholars. Critics argued that PERMA was not a theory of well-being, but rather just a listing of factors that had been shown to be related to well-being (Wong & Roy, Citation2018), that there was no theoretical justification for why these factors related/had to be included (Donaldson et al., Citation2022), that PERMA did not attribute any unique variance in general well-being frameworks, and that it was redundant (Goodman et al., Citation2018). In response, M. Seligman (Citation2018) contended that PERMA was not a framework of what well-being was, but rather a set of elements required to facilitate well-being. He, furthermore, indicated that PERMA was not an exhaustive framework and that it could be expanded. In line with the propositions of Kuhn (Citation1970) and Wallis (2000) on theory development, M. Seligman (Citation2018) proposed six criteria required for expanding the PERMA framework: (a) new elements had to directly relate to well-being, (b) an element had to be pursued in its own right and not as a means to pursue another, (c) new elements had to lead to developmental interventions, (d) all factors had to be parsimonious, (e) PERMA had to be open and flexible to new developments, and (f) each new element had to be independently defined and measured. M. Seligman’s (Citation2018) response and criteria, thus, provided a basis for scientific advancement, as they ‘addressed a number of the criteria underpinning the creation of robust theories: clarifying the purpose of the theory (through highlighting that it’s an approach to rather than of well-being), highlighting what additional types of approaches/elements are needed for its expansion, setting specific criteria for theory development and evaluation and inviting further theorizing’ (Donaldson et al., Citation2022, p. 5).

Similarly, Lomas et al. (Citation2021) presented more explicit criteria for the types of theories, methods, and approaches needed to facilitate scientific advancement in the third wave of positive psychology. They argued that positive psychology had to broaden its scope by developing more contextually relevant theories and employing more systems-informed and cultural/linguistic approaches to theory development (and creating ethical guidelines) and had to expand its methods by employing more qualitative/mixed-method methodologies, using implicit assessment tools, and using more advanced computational approaches to analyze data. Expanding on this narrative, Wissing (Citation2021) postulated the types of holistic perspectives that were required in positive psychology and how contextually specific approaches to positive phenomena had to be approached, as well as highlighting the value of interdisciplinary work. She also highlighted the importance of embedding the theories and methods of positive psychology within its meta-assumptions. Wissing (Citation2021), additionally, laid the foundation for creating more clarity in the world views of positive psychology (ontology, epistemology, and axiology), proposed criteria for expanding its empirical context, identified the types of measurements required, and highlighted the importance of investing in emerging focus domains. Similarly, Pawelski (Citation2016) attempted to provide a descriptive overview of what constituted ‘positive’ in positive psychology and highlighted the six discrete meanings underpinning this from prior research.

Taken together, it was clear that positive psychology researchers had taken heed of prior critiques and had made active attempts to clarify the metatheoretical assumptions of positive psychology. Despite the progress, there are still a number of matters requiring clarity. Positive psychology should attempt to clarify its metaphysical perspective of reality, present a consolidated view of ontological/epistemological/axiological beliefs, clarify and create consensus as to what is considered ‘positive’, address consistencies in and between theories, and develop its own theory of human development. Furthermore, the field should move beyond the positivist paradigm and the accompanying reductionist way of thinking. There is value in adopting either a postpositivist or constructive-interpretivist perspective when exploring/explaining positive psychological phenomena (Wong, Citation2011). Multiple realities exist, and researchers/practitioners cannot be entirely objective or void of bias. Therefore, acknowledging this limitation and appreciating the presence of multiple perspectives and how one’s own biases affect the interpretation of the world may lead to more robust theories and methods (Friedman & Brown, Citation2018). Moreover, specific attention needs to be given to creating ethical decision-making models that inform and evaluate judgements about the values and future priorities of the discipline (Friedman & Brown, Citation2018). Positive psychology should also refrain from reporting and exaggerating sensationalist claims and should acknowledge limitations of important findings (especially when communicated in the public domain).

In addition, positive psychology can apply what has been learnt in other areas, such as the psychology of religion and spirituality, where these problems have largely been resolved. Scholars in the psychology of religion and spirituality present vastly different philosophical world views; yet the field has begun to coalesce around a ‘multi-level interdisciplinary paradigm’ of spirituality (Emmons & Paloutzian, Citation2003; Paloutzian & Park, Citation2005). Here, the aim is to appreciate the unique value each different approach toward spirituality and religion brings to explaining psychological phenomena and allowing for researchers from other domains to operationalize their concepts within this broader framework. This approach will recognize that positive psychology is indeed a ‘psychology’, but will encourage researchers to explore their constructs at different levels of abstraction. It will also allow researchers to compare their findings to, and collaborate more actively with, those from adjacent fields (e.g., anthropology, historical sciences, neurosciences, evolutionary biology, sociology, theology). These adjacent fields have specialized knowledge that explains human flourishing in different ways, and more holistic views can be developed through active collaboration. For positive psychology, this approach will allow for positive psychology researchers’ contributions to be valued (most notably at the individual level) and yet urge researchers to take a broader view of where their work fits into the wider efforts to understand human flourishing better. Therefore, this approach will be non-reductive and will recognize that explaining a phenomenon at one level does not explain it away from others.

Despite these opportunities to develop the philosophy and theorizing underpinning positive psychology, it is unreasonable of critics to assume that complete consensus on all philosophical issues within the discipline can be reached. Critics should consider how fields such as personality psychology operate with theoretical perspectives built on vastly different philosophical foundations. There are fundamental differences in how Freud, Rogers, Skinner, Klein, and others viewed human nature and, thus, presented vastly different approaches to understanding personality development (Allen, Citation2000). Despite these vast differences, scholars do not argue that personality psychology is ‘fundamentally flawed due to a lack of consensus or irreconcilable differences’ in the approaches. Most personality psychologists seem to appreciate ideological pluralism and build on the findings and limitations of other approaches (Cloninger, Citation2009; Strack, Citation2005). For example, the emphasis of behaviorism on overt behavior emerged partially in response to the psychoanalytic view of people as only driven by unobservable unconscious processes (Strack, Citation2005). Similarly, humanistic perspectives partly emerged in response to the behaviorist view of people as merely stimulus-response organisms. These different approaches drew from, and built on, elements of their predecessors.

Our second finding showed that critics highlighted issues with the measurement of positive psychological constructs and with the research methodologies the discipline favored. From the literature, it was clear that critics argued that positive psychology showed poor operationalization and measurement of its constructs, employed flawed research methodologies, over relied on empiricism/positivism, and failed to employ more robust research approaches. These critiques are not unfounded and have been widely acknowledged by positive psychological scientists (e.g., Disabato et al., Citation2019; Donaldson et al., Citation2022; Lomas et al., Citation2021; Van Zyl & Rothmann, Citation2022; Wissing, Citation2021). It is well established that popular positive psychological measuring instruments tend to produce different factorial models, with varying internal consistency ranges between studies and contexts (cf., Disabato et al., Citation2019; Van Zyl & Ten Klooster, Citation2022). For example, the Mental Health Continuum – Short Form (Keyes, Citation2002) and the Grit-O Scale (Duckworth et al., Citation2007) have produced at least 10 different factorial structures, inconsistent findings regarding the factorial equivalence between groups, and reliability indicators ranging from poor to acceptable in different contexts. Furthermore, to ensure acceptable levels of model-data fit, authors have been required to make significant modifications to the factorial structures (e.g., item parceling; Van Zyl & Ten Klooster, Citation2022). Positive psychological researchers have also acknowledged that not all popular psychometric instruments employed robust psychometric test construction principles during their initial development (Van Zyl & Rothmann, Citation2022; Wissing, Citation2021). For example, Van Zyl et al. (Citation2022) highlighted that Govindji and Linley’s (Citation2007) popular strength use and strengths knowledge scales were comprised of a set of self-generated items that had not been pilot-tested, that no evidence as to their face validity was presented, that they only used a single sample and sample population (university students) that were used to ‘validate’ the instrument, and that the items were only subjected to simple principal component analysis. Similarly, Lomas et al. (Citation2021) and Wissing (Citation2021) acknowledged that the discipline favored quantitative research and positivist approaches and relied heavily on self-report measures and cross-sectional over longitudinal designs to investigate claims.

Although the validity of these claims is not disputed, it is important to note that (a) positive psychology is still a relatively new field and (b) these problems plague the entire psychological discipline. First, it is normal for research into new areas or domains to employ ‘quick and dirty’ measures and cross-sectional studies during the first wave of research on novel topics. This practice serves to provide an initial glimpse into previously unstudied or unexplored phenomena. Journal editors are interested in novel work and will tend to overlook methodological simplicity if a study offers new insights or ‘fresh’ ideas. However, as more scientific research on the novel topic starts accumulating, more nuanced research questions emerge. Here, the same simple methodologies and ‘quick and dirty’ measures will not suffice. For this reason, more sophisticated measures and methods will be employed and, eventually, preferred by the scientific community. Over time, methodological standards will progressively be raised. Therefore, the criticisms in this regard do not highlight a fundamental flaw unique to positive psychology, but rather highlight the discourse of the normal scientific enterprise in the early stages. Second, these methods and approaches are not unique to positive psychology. Recent systematic literature reviews regarding the methods and approaches employed in psychology showed that over 90% of publications in psychology were quantitative, most favoring the positivistic approach (Scholtz et al., Citation2020Citation2021; Wilhelmy & Köhler, Citation2022). In their review, Scholtz et al. (Citation2020) showed that only 4.7% of the publications employed a qualitative design and even fewer mixed- or multi-methods. Furthermore, they showed that most publications used cross-sectional and non-experimental research designs, with only 3.9% being longitudinal. These authors also reported that most studies in psychology employed some form of self-report questionnaire (76.8%) to measure psychological phenomena. Similar trends were found in all subdisciplines of psychology, ranging from organizational and social psychology to educational psychology (Coetzee & Van Zyl, Citation2013; McCrudden et al., Citation2019; Sassenberg & Ditrich, Citation2019; Scholtz et al., Citation2021; Wilhelmy & Köhler, Citation2022). Similarly, Reynolds and Livingston (Citation2021) noted that poor test construction processes and practices were apparent in all subdisciplines of psychology, exacerbated by the rapid development of new assessment technologies and analytical approaches.

Given that measurement and methodology are crucial elements for advancing a discipline, positive psychological researchers should be more rigorous in developing and validating new psychometric instruments. There is a need to develop stricter guidelines for developing and validating new instruments and adapting and validating existing methods for new contexts. All positive psychological assessment measures should comply with the International Test Commission (Citation2017) and the European Federation of Psychologists’ Associations (European Federation of Psychologists’ Associations, Citation2013) guidelines on test construction, adaption, and validation, as well as the ISO standards for assessment methods and procedures (International Organization for Standardization, Citation2011). In addition, newly developed psychometric instruments should be subjected to more scrutiny by reviewers and editors, as these are key to addressing issues in the field. Multi-study designs should be favored by following conventional standards in psychometric test development. Separate studies should be used to explore the factorial structure, confirm its factorial validity, explore its factorial equivalence, and establish its predictive validity. Besides this, more attention should be paid to establishing face, discriminant, predictive, and incremental validity of new measures. Given that positive psychology suffers from the ‘jingle-jangle’ fallacy, both researchers and reviewers should be more critical of the unique contribution each new construct or assessment measure makes. As Goodman et al. (Citation2018) point out, there is a significant overlap in psychological constructs, and new constructs do not necessarily explain any new variance in well-being. Furthermore, new psychometric tests should show evidence of their cross-cultural fairness and be developed in line with local traditions and values. Similarly, more innovative analytical approaches should be considered, which compensate for the limitations of current assessment practices (Van Zyl & Ten Klooster, Citation2022). These can include exploratory structural equation modelling (which compensates and controls for differences in the interpretation of items), Bayesian confirmatory factor analysis, machine learning approaches, and the like. There is also an opportunity to develop more objective positive psychological assessment measures to assess positive states/traits/behaviors through kinetic measures, motion capture systems, accelerometers, eye trackers, speech analysis, hormonal endocrinal responses (e.g., cortisol, alpha-amylase), central brain activity (e.g., through electroencephalograms, neuroimaging, electric/magnetic stimulation, connectomes), contextual/attentional measures (e.g., electromagnetic articulography indexing, motion capture systems), and arousal systems (e.g., galvanic skin response, facial electromyography; Cipresso & Immekus, Citation2017). There should additionally be greater focus on incorporating new developments in natural language processing, meta-data mining (e.g., web scraping), and machine learning as methods to assess positive characteristics.

In terms of research methodologies, we echo the calls of Lomas et al. (Citation2021) and Wissing (Citation2021), who state that positive psychology should employ more robust designs (e.g., longitudinal or experimental designs) and approaches such as qualitative, mixed-method, and experimental research. Although these methods and approaches are not entirely absent from the field, they are vastly overshadowed by cross-sectional studies and quantitative research. The overreliance on cross-sectional designs likely feeds the perception that causal inferences are too often inappropriately made within positive psychology. This is a fair concern, even if it applies less to the science itself and more to the exaggerated interpretations of research results often made within the popular psychology literature.

Positive psychologists should, therefore, move away from the reductionist way of thinking by engaging in more phenomenological work as a means of understanding, rather than explaining, psychological experiences. Mixed-method approaches can help explain how and why (or why not) certain factors relate and provide a means to self-correct theories. Here, journals should attempt to showcase these designs and highlight their value to the discipline by calling for more special issues on the topic. Finally, more robust research designs should be utilized. Cross-sectional designs should be limited to exploring ideas, or multiple cross-sectional studies should be published in the same paper to confirm hypotheses. The value of cross-sectional research can be enhanced by using multiple measurement methods and especially by developing and deploying more objective measures to assess positive states, traits, and behaviors.

Growing concerns: a pseudoscience lacking novelty, and self-isolation from general psychology

Stemming from the two roots of the problem, critics had growing concern regarding the status of positive psychology as a science and its relevance to the broader nomological psychological network.

Our third finding showed that positive psychology was seen as a pseudoscience that lacked evidence and showed poor replicability. Critics argued that positive psychology presented (false) claims that were not supported by empirical evidence and that its benefits were vastly exaggerated. Positive psychology was said to be rife with confirmation bias and not self-correcting (i.e., continued adherence to theories that had been empirically discredited rather than updating theoretical assumptions and moving forward). Academic research was focused on generating superficial knowledge, which presented obvious conclusions. The findings also highlighted critics’ belief that positive psychological research findings could not be replicated.

Although some of these critiques have merit, the overarching idea that positive psychology is a pseudoscience is questionable. Curd and Psillos (Citation2014) define a pseudoscience as a set of beliefs, assumptions, statements, or practices about a particular phenomenon that is claimed to be factual and scientific, yet incompatible with the scientific method. According to Curd and Psillos (Citation2014), positive psychology can only be considered a pseudoscience if it meets eight criteria:

  1. It is unfalsifiable (i.e., employing vague, exaggerated, or untestable claims; unable to prove it wrong). Although there are inconsistencies in terminology and theories (as discussed above), positive psychological constructs are, for the most part, clearly defined, with specific indicators/components. Given the ‘over reliance on empiricism’ noted by the critics, mentioned in the previous section, it is clear that hypotheses can be tested and accepted/not accepted.

  2. Collection of evidence is improper (i.e., relying heavily on testimonials; cherry-picking confirming evidence/ignoring disconfirming results). The progress of positive psychology has relied heavily on empiricism and scientism. Although this has resulted in other issues as discussed above, it does support the idea that findings and assumptions are based on scientific evidence that attempts to confirm/disconfirm results. Furthermore, several journals are focused explicitly on collating scientific evidence on positive psychology, along with various societies aimed at disseminating information.

  3. It lacks openness to scrutiny by others. Several authors from adjacent or even unrelated fields (e.g., physics) have scrutinized positive psychological research, processes, and practices. For example, N. J. L. Brown et al. (Citation2013) criticized the analytical strategy used to establish the critical positivity ratio. This, in turn, led to Fredrickson (Citation2013) partially retracting the original paper and responding to the critique. Furthermore, journals such as Frontiers in Psychology (Positive Psychology) invite reviewers from different paradigmatic perspectives to evaluate positive psychological research.

  4. Theory progression is absent (i.e., not self-correcting). This element can, however, not entirely be refuted. Positive psychology does not easily self-correct. For example, despite the paper on the critical positivity ratio being partially retracted, authors are still debating the relevance of the ratio. The original paper continues to garner citations, and the original claims are still positioned as fact in new studies (Friedman and Brown, Citation2018). Van Zyl and Rothmann (Citation2022) argue that researchers rely heavily on ‘contextual factors’ to justify or explain negative results and, therefore, do not self-correct or update existing theories.

  5. Confirmation bias exists (i.e., favoring findings that confirm one’s prior beliefs/assumptions). Confirmation bias is present in all fields of psychology and, therefore, also present in positive psychology. Fairly few studies have been published that show negative results, and there is evidence of data being interpreted to favor inherent beliefs.

  6. It makes exaggerated or extraordinary claims. This element was heavily present during the first decade of the existence of positive psychology and was criticized by both academics and society (cf., Coyne et al., Citation2010). However, during the last decade, scientists have become more cautious about the presentation and interpretation of their results. Yet the problem is quite prolific in the popular psychological press, where findings are taken out of context or over exaggerated, and where causation is often inferred or implied when reporting on correlational research. The problem, therefore, seems to be related to the dissemination of findings to a broader audience rather than the science itself.

  7. It lacks peer review. The vast majority of the journals publishing positive psychological research subject claims to extensive peer review.

  8. Replication of results is poor. The entire discipline of psychology is faced with a replication crisis, and positive psychology is not immune (cf., Efendic & Van Zyl, Citation2019; Maxwell et al., Citation2015). For example, it has been a struggle to replicate findings on the effectiveness of popular positive psychological intervention studies such as the gratitude visit, as well as the three good things exercise, in contexts outside of the USA (Wong & Roy, Citation2018). A number of issues underpin the poor replication of positive psychology: (a) reliance on small, underpowered samples, (b) publication bias, (c) questionable research practices such as p-hacking, (d) a lack of transparency in research practices, and (e) publication pressure and poor funding (Efendic & Van Zyl, Citation2019).

Although there is some justification for the claims made by critics, positive psychology does not seem to conform to the definition of a pseudoscience. There are, however, several areas that warrant further exploration and development. In respect of the lack of replicability and managing confirmation bias, positive psychological journals should actively drive the implementation of open science practices (cf., Van Zyl, Citation2019). Positive psychological journals should consider implementing the transparency and open science promotion guidelines (cf., Nosek et al., Citation2015). These guidelines provide journals with minimum standards for (a) citations plans, (b) data transparency, (c) analytical methods transparency, (d) research materials transparency, (e) research design transparency, (f) pre-registration of studies, (g) pre-registration of analysis plans, and (h) information on how to encourage replication studies (Nosek et al., Citation2015). At a minimum, journals should require authors to submit their raw data and their statistical codes as part of the review process as well as encourage the submission of null results/replication studies. This will allow for more transparency in the theory building and testing process. In addition, journals and editors should encourage pre-registration of studies to reduce ‘analytical flexibility’ and other systematic biases. Pre-registering study protocols may reduce the occurrence of questionable research practices such as HARKing, p-hacking, data fabrication, and the like (Nosek et al., Citation2015; Van Zyl, Citation2019; Van Zyl & Junker, Citation2019). Furthermore, to enhance the quality of peer review, positive psychology journals should consider experimenting with open or collaborative peer review processes. According to Efendic and Van Zyl (Citation2019), collaborative peer review facilitates an open and active dialogue between stakeholders (reviewers/editors/authors) from the original design of a study through to the final submitted manuscript. A collaborative review allows authors to actively engage with reviewers/editors to clarify expectations and discuss content in a meaningful fashion. This reduces reviewer biases, provides opportunities for professional development, ensures transparent feedback, and enhances the quality of the overall manuscript (Dobele, Citation2015; Miller, Citation2006). It is also suggested that the editorial boards of the various top positive psychology journals meet annually to discuss publication trends, share best-practice guidelines, and develop shared strategies to enhance the quality of positive psychological research for the coming year.

Our fourth finding showed that positive psychology lacked novelty and self-isolated from mainstream psychology. Critics contended that positive psychology brought nothing new to the proverbial table and that it willfully created a divide between ‘negative’ psychology and the study of ‘optimal human functioning’ to justify the reason for its existence. In response to these claims, Seligman (Citation2011) confirmed that studying human strengths and virtues was not new and acknowledged the historical origins of the discipline. Seligman (Citation2011) maintained that the origins of ‘positive psychology’ could be traced back to the contributions of William James, Abraham Maslow, Albert Bandura, Carl Rogers, and Victor Frankl (to name a few). The call for a new science with regard to positive experiences, characteristics, and institutions did not disregard these contributions, but rather brought them to the fore and emphasized the need for further development (Seligman & Csikszentmihalyi, Citation2000). This renewed focus on studying what was right, rather than wrong, led to significant contributions to our understanding of well-being and the factors facilitating/undermining it (Seligman, Citation2019). Seligman (Citation2019) argued that positive psychology had produced several unique insights such as that (a) optimists lived longer and healthier lives than pessimists and were less likely to die from cardiovascular disease, (b) women who showed genuine smiles at 18 reported higher levels of marital satisfaction later in life, (c) environmental factors only contributed around 15% of the variance in well-being/happiness, (d) self-discipline and grit were stronger predictors of academic performance than IQ, (e) happy teenagers earned substantially more income 15 years later than their unhappy peers, (f) those who pursued meaningful life experiences had a distinctive genetic profile, and (g) mindfulness interventions could lead to increased resilience. Therefore, positive psychology had played an essential role in advancing our understanding of the human condition.

However, as rightfully stated by critics, Seligman and Csikszentmihalyi’s (Citation2000) call did create a fictitious divide between traditional psychological approaches and positive psychology. This led to several adverse outcomes, as discussed above. This criticism was acknowledged by Seligman (Citation2011Citation2019), who stated that the intent was not to create a divide, but rather to focus more on understanding positive states, traits, behaviors, and institutions. Nevertheless, the discipline has moved beyond this fictitious divide during the last decade. According to Wong (Citation2011), Lomas et al. (Citation2021), and Wissing (Citation2021), positive psychology has started to recognize the value of ‘the negative’ as a means of facilitating positive experiences and that suffering is essential for the development of strengths, happiness, and well-being; consequently, there is a better alignment with mainstream psychological approaches. More recent theoretical frameworks, such as Bohlmeijer and Westerhof’s (Citation2021) model for sustainable mental health, actively incorporate mental illness, dysfunctional cognitions, emotions, and behaviors as part of its ‘positive framework’.

Despite these advancements, there are still some challenges to consider. According to Joseph (Citation2021), despite two decades of debate, there is still no clarity or consensus on the relationship between humanistic psychology and positive psychology. Although various attempts have been made to consolidate the differences and facilitate a more integrative perspective, humanistic psychologists remain critical of positive psychology, and vice versa. Furthermore, most positive psychological interventions and therapy models are built on principles of cognitive-behavioral therapy; yet the discipline does not actively acknowledge this. It, thus, gains value through incorporating approaches that ‘work well’ in other domains in terms of its own theoretical and intervention frameworks. Positive psychology can be further enriched by incorporating more of what can be learnt from other psychological approaches or domains such as systems sciences (M’Pherson, Citation1974), depth psychology (Staude, Citation1976), and evolutionary psychology (Cosmides & Tooby, Citation2013). Moreover, positive psychology should attempt to explore opportunities to incorporate developments from adjacent domains such as the neurosciences, decision sciences, environmental studies, economic sciences, and computer sciences.

Branching out: a harmful decontextualized neo-liberal ideology and capitalistic venture

The criticisms and critiques branched out into two additional areas. Our fifth and sixth findings showed that positive psychology was a decontextualized neo-liberal ideology that caused harm and that it was presented as little more than a capitalistic venture. Positive psychology is classified as a neo-liberalist ideology, where optimal functioning and success are seen as an individual enterprise and a consequence of one’s own life choices. This neo-liberal ideology positions Western values as ‘universal’ and superimposes these onto other cultures. It neglects the role of culture, social context, and the environment in understanding positive phenomena. This, in turn, pathologizes normal human behavior, marginalizes groups, reinforces (gender/cultural) stereotypes, creates stigma, and causes harm.

Clearly not all of positive psychology is fairly captured in these critiques, yet it is a substantial enough problem within the field that these concerns are often raised, and by multiple voices. Marecek and Cristopher (Citation2018) stated that positive psychology had positioned itself as an ‘indigenous psychology’, where positive experiences, characteristics, and phenomena were deemed to be universally relevant and applicable. However, it failed to incorporate indigenous knowledge, social contexts, or cultural perspectives in the pursuit of explaining positive experiences or phenomena (Hendriks et al., Citation2019; Wissing, Citation2021). There are significant differences in how collectivistic and individualistic cultures view mental health and well-being (cf., Hendriks et al., Citation2019); yet the Western model is positioned to be universally applicable (Van Zyl & Rothmann, Citation2022). For example, in African and Eastern cultures, well-being is approached as a function of social contexts (e.g., family functioning, community well-being), whereas in individualistic cultures, the pursuit of well-being is placed solely on the individual (Hendriks et al., Citation2019). Therefore, positive psychological theories, psychometric instruments, and interventions may not be applicable to non-Western cultures (Hendriks et al., Citation2019; Lomas et al., Citation2021; Wissing, Citation2021). This may reinforce cultural stereotypes and create unrealistic expectations about mental health and well-being, which, in turn, may cause significant harm, create stigma, and marginalize certain groups (Hendriks et al., Citation2019; Thompson, Citation2018; Van Zyl & Rothmann, Citation2022).

This critique highlights the need for more culturally relevant or ‘indigenous’ perspectives on positive psychological phenomena that incorporate local traditions, values, and perspectives and present an opportunity for more cross-cultural and cross-national studies in positive psychological phenomena. Echoing the calls of Lomas et al. (Citation2021) and Wissing (Citation2021), there is, thus, a need to further develop a positive cross-cultural psychology, where the specific focus should be on creating more holistic indigenous positive psychological theories, methods, and interventions. Specific attention should also be given to investigating the unique experiences of marginalized or under-represented societal groups (e.g., expatriates and the LGBTQ community) and developing tailored solutions to their unique problems. Here, more participatory action-research-based approaches can be used to allow members of these marginalized communities to co-construct theories, approaches, measures, and solutions alongside academic researchers. Creating a more inclusive culture, where participants are seen as ‘co-developers’ of theories/methods/solutions, can generate unique perspectives on the problems marginalized communities face. Similarly, it is also imperative for positive psychology to create its own ethical research and intervention guidelines to mitigate the potential harm that its theories, methods, and interventions can cause (cf., Jarden et al., Citation2021).

Finally, our results showed that positive psychology was also seen as a capitalistic venture that aimed to commercialize ‘positivity’ as a means to further facilitate individualism, consumerism, and the medicalization of positive experiences. Critics argued that positive psychology created a market of ‘impossible dreams’ that set unrealistic expectations of what a ‘good life’ entailed. It facilitated the medicalization of positive phenomena and, thus, created a market for test developers, consultants, and practitioners to capitalize on people’s ‘pathological unhappiness’.

Although the commercialization of positive psychology cannot be disputed, it is important to reflect on the nature of its intent. No economic, social, or political system, whether it be socialism, capitalism, or communism, is ‘good’ or ‘evil’ by design (Hoppe, Citation1989). The intent driving the system and its implications for society define whether economic, social, or political policies are harmful or beneficial to its constituents (Hoppe, Citation1989). The commercialization of positive psychological tools and techniques indicates their popularity in practice and usefulness to society. Commercial drivers around positive psychological tools and techniques seem to be centered on scalability, with the intent to increase access to valuable resources that can facilitate ‘the good life’ (cf., Richter et al., Citation2021). Scalability requires innovation, physical resources (e.g., information technology (IT) infrastructure), the automation of processes/practices, and people to design content/systems/services. The scalability of a product or service increases accessibility, limits barriers to access, and decreases costs for consumers (Jabłoński & Jabłoński, Citation2020). However, these come at a cost, as the physical resources driving them are finite. So the commercialization of positive psychological tools and techniques helps to facilitate the development of positive states, traits, and behaviors cost-effectively.

It should also be noted that the access to, and the scalability of, positive psychological tools and techniques are not just facilitated by practitioners and industry. Various non-profit organizations, professional societies, and academic institutions provide access to positive psychological tools and techniques at no charge. For example, the Greater Good Science Center aims to provide individuals with easily useable tools and self-development activities to facilitate the development of positive states, traits, and behaviors. Similarly, the University of Pennsylvania provides free access to many positive psychological assessment measures (such as the VIA Signature Strengths Inventory) to help individuals identify their strengths and positive experiences. There are also a number of free (or partially free) apps such as Headspace, Happify, ThinkUp, Happy Habits, and the like that have been developed along with academic institutions to facilitate positive states and behaviors (Feldman, Citation2017). Research entities such as the Optentia in South Africa and the University of Pennsylvania provide free lectures/webinars/workshops, tools, and techniques to upskill practitioners and empower individuals to facilitate their personal growth. There is, thus, a balance between the ‘paid’ and ‘free’ services that aim to increase accessibility to positive psychological tools and techniques.

However, as long as there is a high demand for positive psychological tools, techniques, and interventions, there will always be a gap between what science supports and what practitioners are designing/communicating/implementing (Jarden et al., Citation2021). The challenge for the discipline is, consequently, to (a) work to close the gap by continuing to develop and test interventions, (b) educate practitioners on science/practice integration using the scientist/practitioner or clinical/scholar models of training, (c) urge adherence to the relevant ethical codes (American Psychological Association, American Educational Research Association, etc.) that govern the practice/application of psychology, and (d) educate the public to help them tell the difference between evidence-based practice and quackery.

Limitations and recommendations

Despite attempts to ensure a relevant and rigorous systematic review, there are still a number of limitations to consider. First, confirmation bias may be present, given the nature of this project and that all the authors self-identify as ‘positive psychologists’. To reduce bias, a clear search protocol was established, and specific strategies were implemented (e.g., multiple evaluators/raters were used, inter-rater reliability was calculated, multiple searches were conducted, etc.). Second, no ‘grey literature’ was included in the search protocol. Future research could employ artificial-intelligence-assisted systematic literature review tools to help manage potential biases (cf., Van De Schoot et al., Citation2021). Third, only including academic literature that had been subjected to traditional quality standards and peer review may have led to the exclusion of popular psychology press books/chapters/texts and dissertations/theses that may have presented alternative critiques from different perspectives. Therefore, excluding grey literature may have presented a biased (only academic) view of the criticisms/critiques of positive psychology. Future research could consider conducting a systematic review of grey literature to determine practitioners’ perspectives on the issues within positive psychology. In the fourth place, although the best-practice guidelines for systematic reviews were followed and numerous strategies were considered to ensure that all possible relevant texts were included, there is a possibility that several important manuscripts may have been excluded. For example, Joseph’s (Citation2021) paper was not originally included, as our search and key terms were not present in the title, keywords, or abstract. Finally, the relative importance of the six themes was not established. Although a deductive, theory-driven approach was used to position issues with theory and measurement as the root cause of the other problems, their relative importance was not established. Future research could employ a heuristic iterative classification process with a number of academics and practitioners to determine the relative importance of these criticisms and to generate more holistic solutions to these problems.