Limits...
Reduced fertility in patients' families is consistent with the sexual selection model of schizophrenia and schizotypy.

Del Giudice M - PLoS ONE (2010)

Bottom Line: Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations.This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.These results have important implications for the evolutionary genetics of psychosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Center for Cognitive Science, University of Turin, Torino, Italy. marco.delgiudice@unito.it

ABSTRACT

Background: Schizophrenia is a mental disorder marked by an evolutionarily puzzling combination of high heritability, reduced reproductive success, and a remarkably stable prevalence. Recently, it has been proposed that sexual selection may be crucially involved in the evolution of schizophrenia. In the sexual selection model (SSM) of schizophrenia and schizotypy, schizophrenia represents the negative extreme of a sexually selected indicator of genetic fitness and condition. Schizotypal personality traits are hypothesized to increase the sensitivity of the fitness indicator, thus conferring mating advantages on high-fitness individuals but increasing the risk of schizophrenia in low-fitness individuals; the advantages of successful schzotypy would be mediated by enhanced courtship-related traits such as verbal creativity. Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations. However, most empirical studies find that the reduction in fertility experienced by schizophrenic patients is not compensated for by increased fertility in their unaffected relatives. This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.

Methodology: A simple mathematical model is presented, showing that reduced fertility in the families of schizophrenic patients can coexist with selective neutrality of schizotypy-increasing alleles, or even with positive selection on schizotypy in the general population. If the SSM is correct, studies of patients' families can be expected to underestimate the true fertility associated with schizotypy.

Significance: This paper formally demonstrates that reduced fertility in the families of schizophrenic patients does not constitute evidence against sexual selection on schizotypy-increasing alleles. Futhermore, it suggests that the fertility estimates derived from extant studies may be biased to an unknown extent. These results have important implications for the evolutionary genetics of psychosis.

Show MeSH

Related in: MedlinePlus

The logic of the sexual selection model (SSM) of schizophrenia and schizotypy.In the SSM, schizotypy enhances the sensitivity of a fitness indicator, by affecting brain processes so as to increase verbal/artistic creativity and other mating-related traits. As a result, schizotypal individuals enjoy higher mating and reproductive success when their genetic fitness is high, but suffer a higher risk of schizophrenia and reduced reproductive success when their genetic fitness is low. The figure shows two classes of genetic factors contributing to increased risk of schizophrenia: (a) fitness-reducing mutations and (b) schizotypy-increasing alleles.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3012205&req=5

pone-0016040-g001: The logic of the sexual selection model (SSM) of schizophrenia and schizotypy.In the SSM, schizotypy enhances the sensitivity of a fitness indicator, by affecting brain processes so as to increase verbal/artistic creativity and other mating-related traits. As a result, schizotypal individuals enjoy higher mating and reproductive success when their genetic fitness is high, but suffer a higher risk of schizophrenia and reduced reproductive success when their genetic fitness is low. The figure shows two classes of genetic factors contributing to increased risk of schizophrenia: (a) fitness-reducing mutations and (b) schizotypy-increasing alleles.

Mentions: The fitness indicator model by Shaner and colleagues can be easily integrated with Nettle's original proposal: schizotypy-increasing alleles could affect brain processes so as to increase verbal and artistic creativity (together with other mating-related psychological traits), but the outcomes may be either beneficial (mating success) or deleterious (schizophrenia), depending in part on the individual's genetic fitness and condition [15], [21]. The synthesis of the fitness indicator model with the schizotypy-creativity hypothesis can be labeled the sexual selection model (SSM) of schizophrenia and schizotypy. Figure 1 provides a schematic illustration of the model. It should be noted that, in the SSM, schizophrenia is caused by a combination of genetic factors (fitness-reducing mutations and schizotypy-increasing alleles) and environmental factors that interfere with developmental processes (thereby worsening the organism's condition); thus, the SSM is not inconsistent with the evidence that environmental factors such as drug use, nutritional deficiencies, and infections can increase the risk of schizophrenia (e.g., [22]–[25]).


Reduced fertility in patients' families is consistent with the sexual selection model of schizophrenia and schizotypy.

Del Giudice M - PLoS ONE (2010)

The logic of the sexual selection model (SSM) of schizophrenia and schizotypy.In the SSM, schizotypy enhances the sensitivity of a fitness indicator, by affecting brain processes so as to increase verbal/artistic creativity and other mating-related traits. As a result, schizotypal individuals enjoy higher mating and reproductive success when their genetic fitness is high, but suffer a higher risk of schizophrenia and reduced reproductive success when their genetic fitness is low. The figure shows two classes of genetic factors contributing to increased risk of schizophrenia: (a) fitness-reducing mutations and (b) schizotypy-increasing alleles.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3012205&req=5

pone-0016040-g001: The logic of the sexual selection model (SSM) of schizophrenia and schizotypy.In the SSM, schizotypy enhances the sensitivity of a fitness indicator, by affecting brain processes so as to increase verbal/artistic creativity and other mating-related traits. As a result, schizotypal individuals enjoy higher mating and reproductive success when their genetic fitness is high, but suffer a higher risk of schizophrenia and reduced reproductive success when their genetic fitness is low. The figure shows two classes of genetic factors contributing to increased risk of schizophrenia: (a) fitness-reducing mutations and (b) schizotypy-increasing alleles.
Mentions: The fitness indicator model by Shaner and colleagues can be easily integrated with Nettle's original proposal: schizotypy-increasing alleles could affect brain processes so as to increase verbal and artistic creativity (together with other mating-related psychological traits), but the outcomes may be either beneficial (mating success) or deleterious (schizophrenia), depending in part on the individual's genetic fitness and condition [15], [21]. The synthesis of the fitness indicator model with the schizotypy-creativity hypothesis can be labeled the sexual selection model (SSM) of schizophrenia and schizotypy. Figure 1 provides a schematic illustration of the model. It should be noted that, in the SSM, schizophrenia is caused by a combination of genetic factors (fitness-reducing mutations and schizotypy-increasing alleles) and environmental factors that interfere with developmental processes (thereby worsening the organism's condition); thus, the SSM is not inconsistent with the evidence that environmental factors such as drug use, nutritional deficiencies, and infections can increase the risk of schizophrenia (e.g., [22]–[25]).

Bottom Line: Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations.This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.These results have important implications for the evolutionary genetics of psychosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Center for Cognitive Science, University of Turin, Torino, Italy. marco.delgiudice@unito.it

ABSTRACT

Background: Schizophrenia is a mental disorder marked by an evolutionarily puzzling combination of high heritability, reduced reproductive success, and a remarkably stable prevalence. Recently, it has been proposed that sexual selection may be crucially involved in the evolution of schizophrenia. In the sexual selection model (SSM) of schizophrenia and schizotypy, schizophrenia represents the negative extreme of a sexually selected indicator of genetic fitness and condition. Schizotypal personality traits are hypothesized to increase the sensitivity of the fitness indicator, thus conferring mating advantages on high-fitness individuals but increasing the risk of schizophrenia in low-fitness individuals; the advantages of successful schzotypy would be mediated by enhanced courtship-related traits such as verbal creativity. Thus, schizotypy-increasing alleles would be maintained by sexual selection, and could be selectively neutral or even beneficial, at least in some populations. However, most empirical studies find that the reduction in fertility experienced by schizophrenic patients is not compensated for by increased fertility in their unaffected relatives. This finding has been interpreted as indicating strong negative selection on schizotypy-increasing alleles, and providing evidence against sexual selection on schizotypy.

Methodology: A simple mathematical model is presented, showing that reduced fertility in the families of schizophrenic patients can coexist with selective neutrality of schizotypy-increasing alleles, or even with positive selection on schizotypy in the general population. If the SSM is correct, studies of patients' families can be expected to underestimate the true fertility associated with schizotypy.

Significance: This paper formally demonstrates that reduced fertility in the families of schizophrenic patients does not constitute evidence against sexual selection on schizotypy-increasing alleles. Futhermore, it suggests that the fertility estimates derived from extant studies may be biased to an unknown extent. These results have important implications for the evolutionary genetics of psychosis.

Show MeSH
Related in: MedlinePlus