VI. Earth Life Emergence: Development of Body, Brain, Selves and Societies
1. The Evolution of Cerebral Form and Cognizance
Mashour, George and Michael Alkire. Evolution of Consciousness: Phylogeny, Ontogeny, and Emergence from General Anesthesia. Proceedings of the National Academy of Sciences. 110/Supple. 2, 2013. In this “In the Light of Evolution VII: The Human Mental Machinery” edition, University of Michigan Medical School, and University of California, Irvine, neurophysicians draw upon clinical experience to advance an innovative appreciation of realms of knowing awareness. In regard, a recurrence or recapitulation becomes evident from such reawakenings unto both one’s own sentience, and life’s evolutionary stirrings unto a human acumen to similarly witness and remember. As a result, and as other papers here and across the site (Animal Intelligence), a singular animal encephalization is seen to form and arise by degrees from the earliest proto-cellular origins. With reference to “Evolution of the Avian Brain and Intelligence” by Nathan Emery and Nicola Clayton (Current Biology 15/23, 2005), it is said that the old Scala Naturae from simple rudiments to complex cerebra is to be set aside for a modular, concerted and mosaic increase of cognitive anatomy and function from an original archetype, as if a brain Bauplan, from the outset. As many research fields attest, by an integral vista not possible before, life’s evolution does indeed appear as an embryonic developmental gestation of communal bodies, bilateral brains, and proactive cognizance via creatures in communities.
Are animals conscious? If so, when did consciousness evolve? We address these long-standing and essential questions using a modern neuroscientific approach that draws on diverse fields such as consciousness studies, evolutionary neurobiology, animal psychology, and anesthesiology. We propose that the stepwise emergence from general anesthesia can serve as a reproducible model to study the evolution of consciousness across various species and use current data from anesthesiology to shed light on the phylogeny of consciousness. Ultimately, we conclude that the neurobiological structure of the vertebrate central nervous system is evolutionarily ancient and highly conserved across species and that the basic neurophysiologic mechanisms supporting consciousness in humans are found at the earliest points of vertebrate brain evolution. Thus, in agreement with Darwin’s insight and the recent “Cambridge Declaration on Consciousness in Non-Human Animals,” a review of modern scientific data suggests that the differences between species in terms of the ability to experience the world is one of degree and not kind. (Abstract)
Melchionna, M., et al. Macroevolutionary Trends of Brain Mass in Primates. Biological Journal of the Linnean Society. 129/1, 2020. In this consummate year, nine evolutionary neuroscientists across Italian universities and institutes confirm life’s advancing cerebral encephalization and resultant cognitive attributes on the way to human acumen. And to reflect on their illustrated report, whomever at present is this worldwise personsphere emerging from homo to Anthropo sapience to gain a retrospective vista and import?
A distinctive trait in primate evolution is the expansion in brain mass. The potential drivers of this encephalization process due diversification dynamics are still debated. We assembled a phylogeny for 317 primate species of both extant and extinct taxa so as to identify trends in brain mass evolution. Our findings show that Primates as a whole follow a macroevolutionary increase in accord with more body mass, relative brain size and speciation rate over time. We also find that hominins, starting with Australopithecus africanus in the Oligocene, stand out for distinctly higher rates. (Abstract excerpt)
Montgomery, John and David Bodznick. Evolution of the Cerebellar Sense. Oxford: Oxford University Press, 2016. University of Auckland, New Zealand, and Wesleyan University, USA neuroscientists provide a dedicated introduction to the advent and advance of a cerebellar sense of self and sense of agency. They go on to say how better understandings of our deep neural heritage can aid human rehabilitations, sports, and technology.
The cerebellum is an intriguing component of the brain. In humans it occupies only 10% of the brain volume, yet has approximately 69 billion neurons; that is 80% of the nerve cells in the brain. The cerebellum first arose in jawed vertebrates such as sharks, and early vertebrates also have an additional cerebellum-like structure in the hindbrain. Shark cerebellum-like structures function as adaptive filters to discriminate 'self' from 'other' in sensory. It is likely that the true cerebellum evolved from these cerebellum-like precursors, and that their adaptive filter functionality was adopted for motor control; paving the way for the athleticism and movement finesse that we see in swimming, running, climbing and flying vertebrates.
Montgomery, Stephen, et al. Brain Evolution and Development. Proceedings of the Royal Society B. Vol. 283, Iss. 1838, 2016. Montgomery, a University College London geneticist, with Nicholas Mundy, Cambridge University zoology, and Robert Barton, Durham University anthropology, post a mid 2010s review from their angle, of how brains employ a either a more “concerted” mode whence modular areas evolve together, or a “mosaic” manner where they develop at different rates. Barton has long favored the latter, in contrast to Barbara Finlay and Richard Darlington (search) who proposed the former. See Principles of Brain Evolution by Georg Striedter herein for a balanced treatment.
Phenotypic traits are products of two processes: evolution and development. But how do these processes combine to produce integrated phenotypes? Comparative studies identify consistent patterns of covariation, or allometries, between brain and body size, and between brain components, indicating the presence of significant constraints limiting independent evolution of separate parts. These constraints are poorly understood, but in principle could be either developmental or functional. The developmental constraints hypothesis suggests that individual components (brain and body size, or individual brain components) tend to evolve together because natural selection operates on relatively simple developmental mechanisms that affect the growth of all parts in a concerted manner. The functional constraints hypothesis suggests that correlated change reflects the action of selection on distributed functional systems connecting the different sub-components, predicting more complex patterns of mosaic change at the level of the functional systems and more complex genetic and developmental mechanisms. These hypotheses are not mutually exclusive but make different predictions. We review recent genetic and neurodevelopmental evidence, concluding that functional rather than developmental constraints are the main cause of the observed patterns. (Abstract)
Montiel, Juan and Francisco Aboitiz. Homology in Amniote Brain Evolution. Brain, Behavior and Evolution. 91/2, 2018. From our late global vantage, Chilean neuroscientists can survey past years and decades of neural anatomy studies in a wide context of their embryo-forming mammal, avian, and reptilian occasion. As a result, a shared, repetitive ancestry in kind of genomic circuitry can be seen to persist across this evolutionary heritage. A closing paragraph alludes to a recapitulation of phylogeny and ontogeny. See also From Sauropsids to Mammals and Back: New Approaches to Comparative Cortical Development by Juan Montiel, et al in the Journal of Comparative Neurology (524/3, 2016).
The cerebral hemispheres are the most expanded brain region in most vertebrate lineages, which are generally associated with increases in behavioral complexity. In association with these expansions, the dorsal component of the hemispheres (the pallium) develops diverging morphologies in the various vertebrate classes, making it very difficult to establish correspondences between groups. The best-studied vertebrates in this sense are birds and mammals, which have both developed large brains and elaborate cognitive abilities. Comparing these two types of pallial organizations and establishing homologies between them has been a major challenge for evolutionary neuroanatomy for about a century. Recently, high-throughput analyses of all active transcripts have become a powerful method for comparing brain regions among species and for inferring homologies. (Abstract excerpt)
Moore, Brian. The Evolution of Learning. Biological Reviews. 79/2, 2004. An attempt to draw an “evolutionary cladogram” of pathways for the many modes of animal cerebration such as mimicry, imprinting and imitation. Moore then states that by this scheme, a recapitulation is evident for learning sequences between the ontogeny of an individual organism and the phylogeny of its species.
Morhardt, Ashley. From Fossils to Function: Integrative and Taxonomically Inclusive Approaches to Vertebrate Evolutionary Neuroscience. Brain, Behavior and Evolution. 91/3, 2018. A Washington University neuroscientist introduces this special issue from a 2017 Karger Workshop in Maryland with this title. Among the select papers are Human Paleoneurology and the Evolution of the Parietal Cortex by Emiliano Bruner, Development and Evolution of Cerebral and Cerebellar Cortex by D. Van Essen, et al, and Comparative Primate Connectomics by J. K. Rilling and M. van den Heuvel.
Moroz, Leonid. Biodiversity Meets Neuroscience: From the Sequencing Ship to Deciphering Parallel Evolution of Neural Systems in Omic’s Era. Integrative & Comparative Biology. 55/6, 2015. The University of Florida marine biologist and neuroscientist introduces an Origins of Neurons and Parallel Evolution of Nervous Systems: The Dawn of Neuronal Organization section. As the Abstract notes, by way of research vessel studies of rudimentary nautical life forms, along with laboratory genome sequencings, it is now possible to robustly reconstruct the earliest cerebral-cognitive structures. From this vantage, it is revealed that constant forms were in place from cellular life’s beginnings. As a result, a recurrent convergence in separate lineages and phyla, especially of visual systems, becomes quite evident.
The origins of neural systems and centralized brains are one of the major transitions in evolution. These events might occur more than once over 570–600 million years. The convergent evolution of neural circuits is evident from a diversity of unique adaptive strategies implemented by ctenophores, cnidarians, acoels, molluscs, and basal deuterostomes. But, further integration of biodiversity research and neuroscience is required to decipher critical events leading to development of complex integrative and cognitive functions. Here, we outline reference species and interdisciplinary approaches in reconstructing the evolution of nervous systems. In the “omic” era, it is now possible to establish fully functional genomics laboratories aboard of oceanic ships and perform sequencing and real-time analyses of data at any oceanic location. In doing so, fragile, rare, cryptic, and planktonic organisms, or even entire marine ecosystems, are becoming accessible directly to experimental and physiological analyses by modern analytical tools. Thus, we are now in a position to take full advantages from countless “experiments” Nature performed for us in the course of 3.5 billion years of biological evolution. Together with progress in computational and comparative genomics, evolutionary neuroscience, proteomic and developmental biology, a new surprising picture is emerging that reveals many ways of how nervous systems evolved. (Abstract)
Murray, Elizabeth, et al. The Evolution of Memory Systems. New York: Oxford University Press, 2017. The authors Elizabeth Murray (physiology and psychology) and Steven Wise (neurobiology) are at the National Institute of Mental Health, and Kim Graham is a cognitive neuroscientist at Cambridge University. They accomplish a 500 page treatise on how Earth life came to possess neural capacities to remember and retrieve so as to better survive, evolve and flourish. Five sections are Foundations of Memory systems, Architecture of Vertebrate Memory, Primate Augmentations, Hominin Adaptations, and Deconstructing and Reconstructing Memory Systems. One may add that as this homologous creaturely course reaches our sapient retrospective it quite appears as a long embryonic gestation.
Current theories about human memory have been shaped by clinical observations and animal experiments. This doctrine holds that the medial temporal lobe subserves one memory system for explicit or declarative memories, while the basal ganglia subserves a separate memory system for implicit or procedural memories, including habits. Cortical areas outside the medial temporal lobe are said to function in perception, motor control, attention, or other aspects of executive function, but not in memory. 'The Evolution of Memory Systems' proposes that several memory systems arose during evolution and that they did so for the same general reason: to transcend problems and exploit opportunities encountered by specific ancestors at particular times and places in the distant past. Instead of classifying cortical areas in terms of mutually exclusive perception, executive, or memory functions, the authors show that all cortical areas contribute to memory and that they do so in their own ways-using specialized neural representations.
Negyessy, Laszlo, et al. Convergence and Divergence are Mostly Reciprocated Properties of the Connections in the Network of Cortical Areas. Proceedings of the Royal Society B. 275/2403, 2008. A team of Hungarian neuroscientists report on a systemic complementarity which distinguishes these cortical phenomena, along with a hierarchical division of labor. These findings, if one may reflect, evince once more that a universal dynamics is instantiated in our brains and thought as everywhere else from galaxies to Gaia.
Ng, Renny, et al. Neuronal Compartmentalization: A Means to Integrate Sensory Input at the Earliest Stage of Information Processing. BioEssays. July, 2020. UC San Diego neurobiologists graphically demonstrate how life’s developmental propensity to form functional modules persists from initial rudiments across the span of invertebrate and mammalian species. From the get-go, neural operations are performed by bounded cellular whole units.
In peripheral sense organs, external stimuli are detected by sensory neurons compartmentalized within structures of cuticular or epithelial tissue. Beyond developmental constraints, such compartmentalization allows grouped neurons to functionally interact. Here, we review the prevalence of these units, describe compartmentalized neurons, and consider interactions between cells. Particular attention is paid to insect olfaction with well‐characterized mechanisms of functional, cross‐neuronal interactions. (Abstract excerpt)
Nomura, Tadashi, et al. Reptiles: A New Model for Brain Evo-Devo Research? Journal of Experimental Zoology B. Online January, 2013. Kyoto Prefectural University of Medicine, Ehime University, and National Institute of Neuroscience, Toyko, investigators contend that in the lineage of amniotic, egg laying or bearing, organisms, this ancient Reptilia Class can provide a revealing array of iconic forebears. Telencephalon, diencephalon, optic tectum, cerebellum, and medulla each appear in rudimentary forms. Lizard neurogenesis, for example, can be seen to presage avian and mammalian cerebral plans. Might one then ask, whom as if a similar, nascent global brain/mind is now proceeding altogether to reconstruct this? What kind of an abiding universe tries to learn and achieve, billions of years on, its own self-observation, witness, comprehension, so as to actively, decisively, select itself?
Vertebrate brains exhibit vast amounts of anatomical diversity. In particular, the elaborate and complex nervous system of amniotes is correlated with the size of their behavioral repertoire. However, the evolutionary mechanisms underlying species-specific brain morphogenesis remain elusive. In this review we introduce reptiles as a new model organism for understanding brain evolution. These animal groups inherited ancestral traits of brain architectures. We will describe several unique aspects of the reptilian nervous system with a special focus on the telencephalon, and discuss the genetic mechanisms underlying reptile-specific brain morphology. The establishment of experimental evo-devo approaches to studying reptiles will help to shed light on the origin of the amniote brains. (Abstract)