Molecular archaeology of human cognitive traits

SYSTEM XC- AS A MOLECULAR MECHANISM FOR EVOLUTIONARY NEW FORMS OF ADVANCED COGNITION

Human cognitive abilities are deeply rooted in evolutionary building blocks that maximize computation while maintaining efficiency. These abilities are not without evolutionary signatures; conserved processes like vision have undergone continual phylogenetic adjustments to better serve ecological niches. Conversely, more sophisticated forms of cognition may have required evolutionary innovations to transform existing neuronal processing to expand computational abilities. One such innovation is system xc- (Sxc), a cystine-glutamate antiporter predominantly localized to astrocytes that emerged in deuterostomes (e.g., vertebrates) after their divergence from protostomes over 550 million years ago. Previous evidence suggests that genetically modified rats that lack functional Sxc (MSxc) exhibit enhanced cocaine-seeking behavior. In this study, we deconstructed drug-seeking into its component behaviors, categorizing them as reliant on evolutionary conserved or newly evolved cognitive processes. Our results reveal that Sxc function is dispensable for conserved processes like visual, emotional, and hedonic processing, but critical for advanced, evolutionary new cognitive functions, particularly impulse control and decision making. Notably, we demonstrate a temporally specific reliance on Sxc during the learning phase of optimal decision-making, but not in maintaining established strategies. This is an important addition to our current understanding of astrocytes in non-homeostatic functions, indicating their critical role in computationally demanding phases of learning and memory. Unraveling evolutionary innovations like Sxc not only deepens our understanding of cognitive evolution but also paves the way for revolutionary, precision- targeted therapies in neuropsychiatric disorders, potentially transforming treatment paradigms and patient outcomes.

Tool evolution as a prerequisite for consciousness

Within the concept of the extended mind, the active modification of external objects, externalizations, is seen as an auxiliary means to adapt to the environment. Toolmaking and use are advanced stages of externalizations that evolve. All past or present tools can, theoretically, be precisely assigned a location in an evolutionary tree with predecessors and progeny. Tools are reliably replicated, modified, and selected by their ability to facilitate human needs. Tool evolution, therefore, fulfills Darwinian criteria where the material tool is the phenotype and the instruction to build it is the code. The ostensive triangle consisting of a pointing individual, an observing individual, and a pointed-at object or tool is the germ cell of social transmission of instructions. Tool-building instructions ultimately can be reduced to distinct sequences of motor acts that can be recombined and are socially transmitted. When executed, they replicate tools for the reward of convenience or improved fitness. Tools elicit affordances relating to their use that synchronize different individuals' perceptions, result in psychological "understanding," and thereby modify social networks. Massive tool fabrication as present today in the "tool-sphere" has, therefore, accelerated prosociality and over time led to the acquisition of an individual's third person perspective. The entangled biological evolution accelerated the ongoing cumulative cultural evolution by selecting traits facilitating social transmission. In this context, tool evolution and the corresponding acquired individual instructional content is a precondition to the emergence of higher cognition and "consciousness." A neuroscience investigating externalizations as the starting point of this process is urgently needed.

Towards correlative archaeology of the human mind

Retracing human cognitive origins started out at the systems level with the top-down interpretation of archaeological records spanning from man-made artifacts to endocasts of ancient skulls. With emerging evolutionary genetics and organoid technologies, it is now possible to deconstruct evolutionary processes on a molecular/cellular level from the bottom-up by functionally testing archaic alleles in experimental models. The current challenge is to complement these approaches with novel strategies that allow a holistic reconstruction of evolutionary patterns across human cognitive domains. We argue that computational neuroarcheology can provide such a critical mesoscale framework at the brain network-level, linking molecular/cellular (bottom-up) to systems (top-down) level data for the correlative archeology of the human mind.

An evolutionary perspective on complex neuropsychiatric disease

The forces of evolution-mutation, selection, migration, and genetic drift-shape the genetic architecture of human traits, including the genetic architecture of complex neuropsychiatric illnesses. Studying these illnesses in populations that are diverse in genetic ancestry, historical demography, and cultural history can reveal how evolutionary forces have guided adaptation over time and place. A fundamental truth of shared human biology is that an allele responsible for a disease in anyone, anywhere, reveals a gene critical to the normal biology underlying that condition in everyone, everywhere. Understanding the genetic causes of neuropsychiatric disease in the widest possible range of human populations thus yields the greatest possible range of insight into genes critical to human brain development. In this perspective, we explore some of the relationships between genes, adaptation, and history that can be illuminated by an evolutionary perspective on studies of complex neuropsychiatric disease in diverse populations.

Keeping the balance: Trade-offs between human brain evolution, autism, and schizophrenia

The unique qualities of the human brain are a product of a complex evolutionary process. Evolution, famously described by François Jacob as a “tinkerer,” builds upon existing genetic elements by modifying and repurposing them for new functions. Genetic changes in DNA may lead to the emergence of new genes or cause altered gene expression patterns. Both gene and regulatory element mutations may lead to new functions. Yet, this process may lead to side-effects. An evolutionary trade-off occurs when an otherwise beneficial change, which is important for evolutionary success and is under strong positive selection, concurrently results in a detrimental change in another trait. Pleiotropy occurs when a gene affects multiple traits. Antagonistic pleiotropy is a phenomenon whereby a genetic variant leads to an increase in fitness at one life-stage or in a specific environment, but simultaneously decreases fitness in another respect. Therefore, it is conceivable that the molecular underpinnings of evolution of highly complex traits, including brain size or cognitive ability, under certain conditions could result in deleterious effects, which would increase the susceptibility to psychiatric or neurodevelopmental diseases. Here, we discuss possible trade-offs and antagonistic pleiotropies between evolutionary change in a gene sequence, dosage or activity and the susceptibility of individuals to autism spectrum disorders and schizophrenia. We present current knowledge about genes and alterations in gene regulatory landscapes, which have likely played a role in establishing human-specific traits and have been implicated in those diseases.