What's in a Trait? Reconceptualizing Neurodevelopmental Timing by Seizing Insights From Philosophy

Philosophy has long been debated for its relevance to natural sciences. Here, I exemplify how philosophy contributed to discourses in evolutionary biology concerning the concept of genes and traits. Rather than determining traits, genes influence the plastic development of traits. This dynamic view of traits is of high relevance when trait development depends on sensitive periods, because such interactionist processes link biological variability to environmental factors. I argue that neuroscience can also benefit from conceptual analysis employing philosophical questions. To this end, I use an interactionist approach discussing heterochrony that describes temporal changes of developmental events during evolution. A key example of heterochrony and developmental plasticity is the expansion of the human neocortex. Heterochrony manifests in prolongation of postnatal brain development in modern humans and retention of brain plasticity. Plasticity allows organisms to adapt to fluctuating environments typical for the human cognitive niche, thereby contributing to diversity. While periods of plasticity enable developmental variability, they also introduce the risk of neurodevelopmental aberrations, such as in schizophrenia. Schizophrenia is characterized by an abnormal prolongation of neuroplasticity due to impaired excitatory/inhibitory balance and excessive synaptic pruning, especially in the prefrontal cortex. This "overpruning" combined with delayed maturation may contribute to the disorder's onset and progression. The interplay between environmental factors and neurodevelopment during sensitive periods is crucial in shaping the disease outcome. This interactionist reconceptualization challenges traditional gene-for-trait paradigms and advocates for a focus on developmental timing during different life stages to better understand the etiology of psychopathologies and potential intervention strategies.