Autism and Schizophrenia Are Disorders of Evolvability

摘要

Autism and schizophrenia are of particular interest because new developments in genomic medicine address three aspects of the conditions that have been difficult, thus far, to resolve: their heterogeneity, from subclinical manifestations to disorders that are gravely disabling; the genetic basis for their high heritability; and the persistence of disorders in light of their high heritability but low reproductive success they convey. The origins of autism and schizophrenia, their persistence and heterogeneity can be understood by integrating information from genomic science, the social brain and the evolution of socialization, intelligence and language. Both conditions are associated with structural changes in the genome, specifically copy number variants. Such systemic mutations contribute to an unstable and mutable genome and have been especially notable during primate > hominid evolution. Along with mechanisms that affect gene expression, they contribute to a genome characterized by variability and evolvability. A dynamic and variable genome is reflected by a high degree of phenotypic variation. This, in turn, is reflected in the diversity of neurodevelopmental disorders, in particular autism and schizophrenia. Evolvability is more than a dispositional concept, it is a trait in its own right. In the special case of hominid evolution, evolvability has been both an independent and a dependent variable. Evolution of the modern human brain seems to have arisen during the cultivation of unstable regions in the genome that were conducive to a high degree of inter-individual and inter-generational variation. The consequence of even small aberrations in evolutionary processes and phenotypic variations is most likely to be manifest in the functions of the social brain: self-referential processing, perspective taking and the dual components of empathy; also language as well as intelligence itself. The trade-off is a dynamic genome that can rearrange itself in untoward ways and may be felt in one or more of the above functions. The occurrence of neurodevelopmental disorders ranging from the learning disabilities and ADD to autism and schizophrenia, are epiphenomenal to a genome that is unstable and mutable. The selective advantage of such a genome is the runaway evolution of positive prosocial and intellective traits. If there is a core to the pathology that emerges in autism and schizophrenia, it is at the genomic level, and is probably related to the unique evolvability of the human genome. Genetic transformation as an agent of evolvability is necessarily associated with untoward consequences. Just as point mutations may have deleterious effects, so do genomic transformations. The neurodevelopmental disorders, therefore, are the consequence of evolvability.