The Elusive “Developmental Mechanism”: What they are and how to study and test them

Few issues have garnered as much attention as that of understanding mechanisms of developmental change. Understanding mechanisms of developmental change is important because it allows researchers to go beyond studying at what age an ability emerges to understanding the processes by which those abilities develop in the first place. Despite the clear importance of mechanisms, the notion of a developmental mechanism or mechanism of developmental change remains largely undefined and there exists no clear guidance on how to study these mechanisms systematically in the developmental literature. Given these outstanding questions, this paper has two main aims. The first aim was to provide a clear definition of mechanisms of developmental change that aligns most closely with how most, if not all, developmental psychologists think about developmental mechanisms. The second goal was to provide concrete suggestions for how developmental scientists might study and test different kinds of mechanisms of developmental change based on their perceived manipulability. One of the main arguments of the paper is that there is no one-size-fits-all approach to studying and testing mechanisms of developmental change and that how developmental researchers study them depends crucially on their perceived manipulability.

Population-level asymmetry of the cerebral cortex: reproducibility, lifespan changes, heritability, and individual differences

Cortical asymmetry is a ubiquitous feature of brain organization that is altered in neurodevelopmental disorders and aging. Achieving consensus on cortical asymmetries in humans is necessary to uncover the genetic-developmental mechanisms that shape them and factors moderating cortical lateralization. Here, we delineate population-level asymmetry in cortical thickness and surface area vertex-wise in 7 datasets and chart asymmetry trajectories across life (4-89 years; observations = 3937; 70% longitudinal). We reveal asymmetry interrelationships, heritability, and test associations in UK Biobank (N=~37,500). Cortical asymmetry was robust across datasets. Whereas areal asymmetry is predominantly stable across life, thickness asymmetry grows in development and declines in aging. Areal asymmetry correlates in specific regions, whereas thickness asymmetry is globally interrelated across cortex and suggests high directional variability in global thickness lateralization. Areal asymmetry is moderately heritable (max h2SNP ~19%), and phenotypic correlations are reflected by high genetic correlations, whereas heritability of thickness asymmetry is low. Finally, we detected an asymmetry association with cognition and confirm recently-reported handedness links. Results suggest areal asymmetry is developmentally stable and arises in early life, whereas developmental changes in thickness asymmetry may lead to directional variability of global thickness lateralization. Our results bear enough reproducibility to serve as a standard for future brain asymmetry studies.

(Non)Parallel developmental pathways to vertebrate appendage reduction and loss

This is the pre-peer reviewed version of the following article: (Non)Parallel developmental mechanisms in vertebrate appendage reduction and loss , which has been published in final form at https://doi.org/10.1002/ece3.8226. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Appendages have been reduced or lost hundreds of times independently during vertebrate evolution. This suggests that selection routinely favors appendage reduction. How often are the same developmental and genetic pathways used during loss by independent lineages? We reviewed the developmental and evolutionary literatures of appendage reduction in 12 genera spanning fish, reptiles, birds, and mammals. We found that appendage reduction and loss resulted from modified gene expression in each case but one. However, the genes for which expression was modified were rarely shared. Our findings suggest that adaptive loss of complex traits might proceed relatively easily through changes in gene expression along multiple developmental pathways.

Human Culture and Cognition

<p>Human behaviour is largely influenced by culture. Culture evolves cumulatively over time. The origins of culture in our lineage necessitated the evolution of psychological biases so humans could tractably navigate the emerging information environment. I examine the nature of these biases and conclude that they are unlikely to be genetically coded to any significant degree. This is because of the flexibility such biases needed to possess in the face of fluid cultural environments and because of the developmental mechanisms of the brain. I further outline three possible views on what the nature of the information these biases act upon might be. First there is the view that cultural information is constructed and held in individual minds but does not flow in any meaningful replicative fashion between minds. Second is the view that culture is information distributed in a population and cultural evolution is the temporal change of this populationlevel information as a result of low fidelity individual copying events. Finally, I argue that meme theory, which asserts that culture is usefully seen as bits of information that replicate in transmission, is a fruitful model of cultural evolution. Keywords Cognition, cultural evolution, culture, evolutionary psychology, memes, neuroconstructivism, psychological biases.</p>

Human Culture and Cognition

<p>Human behaviour is largely influenced by culture. Culture evolves cumulatively over time. The origins of culture in our lineage necessitated the evolution of psychological biases so humans could tractably navigate the emerging information environment. I examine the nature of these biases and conclude that they are unlikely to be genetically coded to any significant degree. This is because of the flexibility such biases needed to possess in the face of fluid cultural environments and because of the developmental mechanisms of the brain. I further outline three possible views on what the nature of the information these biases act upon might be. First there is the view that cultural information is constructed and held in individual minds but does not flow in any meaningful replicative fashion between minds. Second is the view that culture is information distributed in a population and cultural evolution is the temporal change of this populationlevel information as a result of low fidelity individual copying events. Finally, I argue that meme theory, which asserts that culture is usefully seen as bits of information that replicate in transmission, is a fruitful model of cultural evolution. Keywords Cognition, cultural evolution, culture, evolutionary psychology, memes, neuroconstructivism, psychological biases.</p>

A Dual Role for Behavior in Evolution and Shaping Organismal Selective Environments

The hypothesis that evolved behaviors play a determining role in facilitating and impeding the evolution of other traits has been discussed for more than 100 years with little consensus beyond an agreement that the ideas are theoretically plausible in accord with the Modern Synthesis. Many recent reviews of the genomic, epigenetic, and developmental mechanisms underpinning major behavioral transitions show how facultative expression of novel behaviors can lead to the evolution of obligate behaviors and structures that enhance behavioral function. Phylogenetic and genomic studies indicate that behavioral traits are generally evolutionarily more labile than other traits and that they help shape selective environments on the latter traits. Adaptive decision-making to encounter resources and avoid stress sources requires specific sensory inputs, which behaviorally shape selective environments by determining those features of the external world that are biologically relevant. These recent findings support the hypothesis of a dual role for behavior in evolution and are consistent with current evolutionary theory.

(Non)Parallel developmental pathways to vertebrate appenda

This is the pre-peer reviewed version of the following article: (Non)Parallel developmental mechanisms in vertebrate appendage reduction and loss , which has been published in final form at https://doi.org/10.1002/ece3.8226. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Appendages have been reduced or lost hundreds of times independently during vertebrate evolution. This suggests that selection routinely favors appendage reduction. How often are the same developmental and genetic pathways used during loss by independent lineages? We reviewed the developmental and evolutionary literatures of appendage reduction in 12 genera spanning fish, reptiles, birds, and mammals. We found that appendage reduction and loss resulted from modified gene expression in each case but one. However, the genes for which expression was modified were rarely shared. Our findings suggest that adaptive loss of complex traits might proceed relatively easily through changes in gene expression along multiple developmental pathways.