VI. Life’s Cerebral Cognizance Becomes More Complex, Smarter, Informed, Proactive, Self-Aware

B. A Neural Encephalization from Minimal Stirrings to an Earthuman Cognizance

Hartenstein, Volker and Angelika Stollewerk. The Evolution of Early Neurogenesis. Developmental Cell. 32/4, 2016. As our nascent cerebral humankinder reconstructs how we came to be ourselves, UCLA and Queen Mary University of London evo/devo neuroscientists provide a comparative overview of neural progenitors across the animal kingdom, along with neurogenetic mechanisms which form embryonic brains.

The foundation of the diverse metazoan nervous systems is laid by embryonic patterning mechanisms, involving the generation and movement of neural progenitors and their progeny. Here we divide early neurogenesis into discrete elements, including origin, pattern, proliferation, and movement of neuronal progenitors, which are controlled by conserved gene cassettes. We review these neurogenetic mechanisms in representatives of the different metazoan clades, with the goal to build a conceptual framework in which one can ask specific questions, such as which of these mechanisms potentially formed part of the developmental “toolkit” of the bilaterian ancestor and which evolved later. (Abstract)

Neurogenesis before the Rise of Bilaterian Animals: Cnidaria and Ctenophora are the first metazoan clades with neurons, even though the molecular machinery enabling a cell to sense external stimuli and generate/conduct electric impulses evolved much earlier in single-cell organisms. Accordingly, in the first multicellular animals that lacked a nervous system (e.g., sponges), one can detect different types of cells that already encapsulate many aspects of neurons. (394) During embryonic development, proneural genes and the Notch signaling pathway control the number and pattern of flask cells. This or related cell types could have given rise to the neurons that occurred in the common ancestor of bilaterians and cnidarians. (394)

Hartenstein, Volker, et al. Modeling the Developing Drosophila Brain. BioScience. 58/9, 2008. By creative employ of digital three-dimensional models, UCLA developmental biologists provide a graphic display of the compartmental and hierarchic maturation of the fly brain from neurons and axons to a macrocircuit anatomy.

Harzsch, Steffan, ed. Development of the Arthropod Nervous System: A Comparative and Evolutionary Approach. Arthropod Structure & Development. 32/3-4, 2003. An update to the volume by Breidbach and Kutsch above, with contributions on invertebrate neurogenesis in chelicerates, crustaceans and hexapods.

Haun, Daniel, et al. Origins of Spatial, Temporal and Numerical Cognition. Trends in Cognitive Sciences. 14/12, 2010. In a special issue on the subject, psychologists and anthropologists from Germany, England, Italy, and the Netherlands, including Nicola Clayton and Giorgio Vallortigara, attest to a progression of complex brains and their acuities which is now realized to grace and orient the span of life’s emergent evolution.

Herculano-Houzel, Suzana. Coordinated Scaling of Cortical and Cerebellar Numbers. Frontiers in Neuroanatomy. 4/Article 12, March, 2010. A further exposition by the Brazilian researcher in favor of brain evolution “in concert” via a “universal numerical relationship” that spans the sequence of mammalian species. We people possess a highest, optimum neuron population and complex net arrangement, but what makes us extra special is our membership in the major evolutionary transition to a social worldwide collective intelligence.

Here I show for the first time that the numbers of neurons in the cerebral cortex and cerebellum are directly correlated across 19 mammalian species of four different orders, including humans, and increase concertedly in a similar fashion both within and across the orders Eulipotyphla (Insectivora), Rodentia, Scandentia and Primata, such that on average a ratio of 3.6 neurons in the cerebellum to every neuron in the cerebral cortex is maintained across species. This coordinated scaling of cortical and cerebellar numbers of neurons provides direct evidence in favor of concerted function, scaling and evolution of these brain structures, and suggests that the common notion that equates cognitive advancement with neocortical expansion should be revisited to consider in its stead the coordinated scaling of neocortex and cerebellum as a functional ensemble. (Abstract, 1)

Herculano-Houzel, Suzana. The Human Brain in Numbers: A Linearly Scaled-up Primate Brain. Frontiers in Human Neuroscience. 3/Art. 31, November, 2009. From our late vantage, humankind’s collaborative facility is progressively reconstructing the Metazoan neural architectures it arose from. By way of novel instrumentation, an Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, neuroscientist here argues for an evolutionary continuum best tracked by the number and density of neurons and networks. As a result, prior views of encephalization by brain size or mosaic areas are set aside for a concerted, integrative cerebral coordination. While human brains possess a premier neuronal quantity, this can be set in a constant train with life’s long cognitive ramification.

To conclude that the human brain is a linearly scaled-up primate brain, with just the expected number of neurons for a primate brain of its size, is not to state that it is unremarkable in its capabilities. However, as studies on the cognitive abilities of non-human primates and other large-brained animals progress, it becomes increasingly likely that humans do not have truly unique cognitive abilities, and hence must differ from these animals not qualitatively, but rather in the combination and extent of abilities such as theory of mind, imitation and social cognition. (8)

Hofman, Michel. Evolution and Complexity of the Human Brain. Gerhard Roth and Mario Wullimann, eds. Brain Evolution and Cognition. Heidelberg: Spektrum, 2001. Common organizing principles are seen to persist throughout their evolutionary ramification which then suggests an archetypal Bauplan. Since we posted this in March 2004, the Netherlands Institute for Neuroscience researcher has stayed on message. See for example a 2014 paper Evolution of the Human Brain in Frontiers in Neuroanatomy (Vol. 8/Art. 15).

It is evident that the potential for brain evolution results not from the unorganized aggregations of neurons but from cooperative associations by the self-similar compartmentalization and hierarchical organization of neural circuits and the invention of fractal folding, which reduces the interconnective axonal distances. (518)

Holland, Linda, et al. Evolution of Bilaterian Central Nervous Systems: A Single Origin? EvoDevo. 4/Art. 27, 2013. In this new online journal from BioMed Central, a team of American, French, British and Taiwanese marine biologists, drawing on research findings going back to the 1980s are able, as others also, to now reach a mature conclusion. The answer is Yes. From “urbilaterian” rudiments in the earliest organisms a common ramification of neural anatomy and physiology is seen to radiate and elaborate. For a similar view, see Evidence for Deep Regulatory Similarities in Early Developmental Programs across Highly Diverged Insects by Majid Kazemian, et al (search).

Thus, their expression is a better criterion for CNS homologs than the expression of anterior/posterior patterning genes, many of which (for example, Hox genes) are similarly expressed both in the CNS and in the remainder of the ectoderm in many bilaterians. The evidence leaves hemichordates in an ambiguous position – either CNS centralization was lost to some extent at the base of the hemichordates, or even earlier, at the base of the hemichordates + echinoderms, or one of the two hemichordate nerve cords is homologous to the CNS of protostomes and chordates. In any event, the presence of part of the genetic machinery for the anterior neural ridge, the zona limitans intrathalamica and the isthmic organizer in invertebrate chordates together with similar morphology indicates that these organizers were present, at least in part, at the base of the chordates and were probably elaborated upon in the vertebrate lineage. (Abstract)

There is general agreement that the relatively complex central nervous system (CNS) characterizing most higher metazoan animals can be traced back through evolution to a nerve net in a cnidarian-like ancestor. (1) In sum, similar expression patterns of developmental genes involved in both A/P and D/V patterning in the protostome and chordate nerve cords as well as anatomical and functional similarities support the view that the ancestral bilaterian had a CNS. (15)

EvoDevo publishes articles on a broad range of topics associated with the translation of genotype to phenotype in a phylogenetic context. Understanding the history of life, the evolution of novelty and the generation of form, whether through embryogenesis, budding, or regeneration are amongst the greatest challenges in biology. We support the understanding of these processes through the many complementary approaches that characterize the field of evo-devo.

Hopfield, John. Neural Networks and Physical Systems with Emergent Collective Computational Abilities. Proceedings of the National Academy of Sciences. 79/2554, 2011. A latest contribution by the renowned Princeton biophysicist who at Caltech wrote the original paper describing neural networks. Some three decades later this self-organized complex network revolution in neuroscience is now reaching a robust veracity and acceptance via its worldwide collaboration.

Computational properties of use to biological organisms or to the construction of computers can emerge as collective properties of systems having a large number of simple equivalent components (or neurons). (2554)

Innocenti, Giorgio and Jon Kaas. The Cortex. Trends in Neuroscience. 18/9, 1995. A special issue devoted to the evolutionary emergence of the mammalian neocortex. There is a homologous correspondence and similarity among species in brain design with regard to overall dimensions and the number of connected neurons.

Iwaniuk, Andrew, et al. A Mosaic Pattern Characterizes the Evolution of the Avian Brain. Proceedings of the Royal Society of London B. Biology Letters S. 4, 2004. Two main theories are in play for how brains evolve and grow in size. The “developmental constraints” view says that modular brain regions scale-up together. A “mosaic” school argues that these specific areas change in size independently of each other. The authors lean toward the latter for birds, but advise that both modes are variously going on during vertebrate cerebral evolution.

Jerison, Harry. On the Evolution of Mind. David Oakley, ed. Brain and Mind. London: Metheun, 1985. A pioneer in the field explains how large brains, as information processing systems, are arranged in a nested hierarchical fashion.

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