The cliff edge model of the evolution of schizophrenia: Mathematical, epidemiological, and genetic evidence

How has schizophrenia, a condition that significantly reduces an individual's evolutionary fitness, remained common across generations and cultures? Numerous theories about the evolution of schizophrenia have been proposed, most of which are not consistent with modern epidemiological and genetic evidence. Here, we briefly review this evidence and explore the cliff edge model of schizophrenia. It suggests that schizophrenia is the extreme manifestation of a polygenic trait or a combination of traits that, within a normal range of variation, confer cognitive, linguistic, and/or social advantages. Only beyond a certain threshold, these traits precipitate the onset of schizophrenia and reduce fitness. We provide the first mathematical model of this qualitative concept and show that it requires only very weak positive selection of the underlying trait(s) to explain today's schizophrenia prevalence. This prediction, along with expectations about the effect size of schizophrenia risk alleles, are surprisingly well matched by empirical evidence. The cliff edge model predicts a dynamic change of selection of risk alleles, which explains the contradictory findings of evolutionary genetic studies.

Evolutionary perspectives on substance and behavioural addictions: Distinct and shared pathways to understanding, prediction and prevention

Addiction poses significant social, health, and criminal issues. Its moderate heritability and early-life impact, affecting reproductive success, poses an evolutionary paradox: why are humans predisposed to addictive behaviours? This paper reviews biological and psychological mechanisms of substance and behavioural addictions, exploring evolutionary explanations for the origin and function of relevant systems. Ancestrally, addiction-related systems promoted fitness through reward-seeking, and possibly self-medication. Today, psychoactive substances disrupt these systems, leading individuals to neglect essential life goals for immediate satisfaction. Behavioural addictions (e.g. video games, social media) often emulate ancestrally beneficial behaviours, making them appealing yet often irrelevant to contemporary success. Evolutionary insights have implications for how addiction is criminalised and stigmatised, propose novel avenues for interventions, anticipate new sources of addiction from emerging technologies such as AI. The emerging potential of glucagon-like peptide 1 (GLP-1) agonists targeting obesity suggest the satiation system may be a natural counter to overactivation of the reward system.

Adaptive Calibration of Dyadic Sexual Desire Is Sex Differentiated and Disrupted by Hormonal Contraceptives

Adaptive calibration models suggest that features of people's childhood ecologies can shape their reproductive outcomes in adulthood. Given the importance of dyadic sexual desire (i.e., desire for sex with a partner) for relationships and reproduction, we examined the extent to which people's childhood ecologies-especially the unpredictability of those ecologies-adaptively calibrate such desire. Nevertheless, because female (versus male) sexual desire is presumed to be more sensitive to situational factors, and because hormonal contraceptives alter myriad aspects of female physiology that influence female sexual desire, we predicted that adaptive calibration of dyadic sexual desire would emerge more strongly for naturally cycling females (versus females who use hormonal contraceptives and versus males). In Study 1, a total of 630 participants (159 males, 203 naturally cycling females, and 268 females using hormonal contraceptives) completed questionnaires assessing the harshness and unpredictability of their childhood ecologies as well as their sexual desire. Consistent with predictions, childhood unpredictability (but not harshness) was positively associated with dyadic (but not solitary) sexual desire among naturally cycling females (but not among females using hormonal contraceptives nor among males). Study 2, which consisted of 736 females (307 naturally cycling females, 429 females using hormonal contraceptives), replicated this pattern of results for females. These findings add to a growing literature suggesting that the instability of people's early childhood ecologies can adaptively calibrate their adult reproductive motivations and behaviors, including their dyadic sexual desire. Not only is the current finding among the first to show that some adaptive calibration processes may be sex differentiated, it further highlights that hormonal contraceptives, which alter the evolved reproductive physiology of females, may disrupt adaptive calibration processes (though such disruption may not be inherently negative).

Development and psychometric evaluation of the Anticipated Food Scarcity Scale (AFSS)

Mass media extensively inform societies about events threatening the global food supply (e.g., pandemics or Brexit). Consumers exposed to such communication may perceive food resources as becoming scarcer. In line with an evolutionary account, these perceptions can shift decision-making in domains such as food preferences or prosociality. However, existing literature has solely focused on actual and past food insecurity experiences threatening mostly low-income families, thus neglecting the future-oriented perceptions among the general population. This paper broadens the food insecurity research scope by developing a new construct-anticipated food scarcity (AFS)-which is defined as the perception that food resources are becoming less available (in the future). We have developed and psychometrically validated the 8-item Anticipated Food Scarcity Scale (AFSS) in eight studies (N = 1333). The 8-item AFSS is unidimensional and has good psychometric qualities. The scale is sensitive to food scarcity cues and, therefore, can be used in experimental research. Moreover, its relatively narrow set of items makes it an exceptionally potent tool for use in online surveys, field settings, and lab studies. Taken together, the AFSS presents an alternative approach to food scarcity measurement in affluent societies and, consequently, can foster novel research on food waste, prosocial behaviors, and other similar topic areas.

The Evolutionarily Mismatched Impact of Urbanization on Insomnia Symptoms: a Short Review of the Recent Literature

PURPOSE OF REVIEW

For the most part of human existence, individuals have been living a rural lifestyle in a rural setting. However, such sleep-conducive conditions have largely been transformed dramatically by urbanization within a relatively short span of time in recent history, and the resulting evolved mechanisms-environment mismatch is theorized to bring about an increased risk for insomnia symptoms. This brief review of the recent literature is designed to evaluate the veracity of this proposition.

RECENT FINDINGS

The majority of recent findings have suggested that most proposed evolutionarily mismatched urban factors are indeed related to the presence of insomnia symptoms. However, there is a general paucity of longitudinal evidence (and for some other factors, a lack of enough evidence of any kind). Although there is a preponderance of recent findings indicating a link between evolutionarily mismatched urban phenomena and insomnia symptoms, more longitudinal data are needed before any causative conclusion can be drawn.

Out of balance: the role of evolutionary mismatches in the sex disparity in autoimmune disease

Over the past century autoimmune disease incidence has increased rapidly in (post-) industrialised, affluent societies, suggesting that changes in ecology and lifestyle are driving this development. Epidemiological studies show that (i) 80% of autoimmune disease patients are female, (ii) autoimmune diseases co-occur more often in women, and (iii) the incidence of some autoimmune diseases is increasing faster in women than in men. The female preponderance in autoimmunity is most pronounced between puberty and menopause, suggesting that diverging sex hormone levels during the reproductive years are implicated in autoimmune disease development. Using an evolutionary perspective, we build on the hypotheses that female immunity is cyclical in menstruating species and that natural selection shaped the female immune system to optimise the implantation and gestation of a semi-allogeneic foetus. We propose that cyclical immunomodulation and female immune tolerance mechanisms are currently out of balance because of a mismatch between the conditions under which they evolved and (post-)industrialised, affluent lifestyles. We suggest that current changes in autoimmune disease prevalence may be caused by increases in lifetime exposure to cyclical immunomodulation and ovarian hormone exposure, reduced immune challenges, increased reproductive lifespan, changed reproductive patterns, and enhanced positive energy balance associated with (post-)industrialised, affluent lifestyles. We discuss proximate mechanisms by which oestrogen and progesterone influence tolerance induction and immunomodulation, and review the effect of the menstrual cycle, pregnancy, and contraceptive use on autoimmune disease incidence and symptoms.

Inflammatory bowel diseases, the hygiene hypothesis and the other side of the microbiota: Parasites and fungi

This review tackles the concept of the evolutionary mismatch, in relation with the reduction of the prevalence of the so-called "dirty old friends". These formed the variegated community of parasites and microorganisms, either prokaryotic or eukaryotic, that, over long evolutionary times, co-evolved with humans and their ancestors, inhabiting their digestive tracts, and other body districts. This community of microbial symbionts and metazoan parasites is thought to have evolved a complex network of inter-independence with the host, in particular in relation with their immune stimulating capacity, and with the consequent adaptation of the host immune response to this chronic stimulation. Strictly related to this evolutionary mismatch, the hygiene hypothesis, proposed by David Strachan in 1989, foresees that the increase in the incidence of inflammatory and autoimmune disorders during the twentieth century has been caused by the reduced exposure to parasites and microorganisms, especially in industrialized countries. Among these pathologies, inflammatory bowel diseases (IBDs) occupy a prominent role. From these premises, this review summarizes current knowledge on how variations in the composition of the gut bacterial microbiota, as well as its interactions with fungal communities, influence the overall immune balance, favouring or counteracting gut inflammation in IBDs. Additionally, the effect of worm parasites, either directly on the immune balance, or indirectly, through the modulation of bacterial and fungal microbiota, will be addressed. Finally, we will review a series of studies related to the use of molecules derived from parasitic worms and fungi, which hold the potential to be developed as postbiotics for the treatment of IBDs.

Impact of reproductive evolutionary mismatch on women's health and the need for action and research

Efforts by the health and scientific community have focused on providing women with the means to control and regulate their fertility. We paid less attention to the reality of women achieving their reproductive revolution while burdened with a reproductive system that evolved to fit the life of our ancestor hunter-gatherers, where women were destined to spend most of their reproductive years pregnant or breastfeeding. This state of evolutionary mismatch impacts on women's health as the reproductive system continues incessantly to work, producing a monthly ovum and exposing the reproductive organs to cyclic hormonal stimulation without the benefit of pregnancy and breastfeeding. Women have to cope with a life of menstrual cycles, decreased fecundity owing to reproductive ageing, and a higher risk of reproductive cancers, in addition to uterine fibroids, and endometriosis. The burden will increase in low-resource countries as more women are adopting the new model of reproductive behavior, and resources to cope with the impact are limited. The reproductive revolution is benefiting not only women, but also their societies and the world at large. The health profession and the scientific community have an obligation to support women to cope with the impact of reproductive evolutionary mismatch.

A teleofunctional account of evolutionary mismatch

When the environment in which an organism lives deviates in some essential way from that to which it is adapted, this is described as "evolutionary mismatch," or "evolutionary novelty." The notion of mismatch plays an important role, explicitly or implicitly, in evolution-informed cognitive psychology, clinical psychology, and medicine. The evolutionary novelty of our contemporary environment is thought to have significant implications for our health and well-being. However, scientists have generally been working without a clear definition of mismatch. This paper defines mismatch as deviations in the environment that render biological traits unable, or impaired in their ability, to produce their selected effects (i.e., to perform their proper functions in Neander's sense). The machinery developed by Millikan in connection with her account of proper function, and with her related teleosemantic account of representation, is used to identify four major types, and several subtypes, of evolutionary mismatch. While the taxonomy offered here does not in itself resolve any scientific debates, the hope is that it can be used to better formulate empirical hypotheses concerning the effects of mismatch. To illustrate, it is used to show that the controversial hypothesis that general intelligence evolved as an adaptation to handle evolutionary novelty can, contra some critics, be formulated in a conceptually coherent way.