Brain evolution crosses an ontogenetic 'ant's country' that escapes analysis
Brain evolution crosses an ontogenetic 'ant's country' that escapes analysis
The central idea I want to present is that the brain of vertebrates is highly complex structurally. This is due to developmental mechanisms that regionalize its primordium in multiple independent histogenetic units. Rather than chaotic, this process is highly ordered, since it is fundamented on a hierarchic inherited Bauplan that is strongly conserved evolutionarily. The independent histogenetic units of the brain wall (composed of progenitors) obtain each a distinct genetic profile based on an unique combination of approximately hundred developmental genes (minimally). As a result, these units regulate individually developmental variables controlling growth (proliferation and patterns of neurogenesis) as well as differentiation of the neuronal daughter cells (neuronal typology and positioning in the brain, and their axonal navigation leading to sinaptogénesis). All this is previous to any functions, which will eventually appear once they are possible. Each areal histogenetic process is strictly causal and obeys the structural master plan (thats's why we invariably detect homologies when we compare the brains of diverse vertebrate species). Each unit creates just a small part of the whole edifice, and may collaborate in some other parts by contributing needed cells, or trophic factors, for instance. However, the enormous multiplicity of such units and the increment in complexity generated as progenitors produce vast amounts of neurons that interconnect one with another in complex arrays generates a gigantic amount of developing causal phenomena in a multilevel system of parts. This level of complexity makes it practically impossible to predict the final result. Nevertheless, a reasonable end result -a normal brain- obtains in most ontogenies. This situation corresponds to the "Ant's Country" described by Ian Stewart and Jack Cohen in "Figments of Reality. The Evolution of the Curious Mind" (Cambridge Univ. Press 1997). In Ant's Country unfathomable causal paths among numbers of paths that escape our calculation powers repeatedly lead finally to a recognizable result. I suppose that changes in brain evolution occur by emergence of novel routes across this complexly causal Ant's Country resulting from the diverse ontogenetic potencies. The evolved complex ontogenetic system is apparently highly canalized in the genome (insured from failure by many redundant gene actors) and it accordingly tends to produce once and again a brain capable of functioning, though it is practically impossible to discern the molecular and cellular details that cause an adaptative brain.
The central idea I want to present is that the brain of vertebrates is highly complex structurally. This is due to developmental mechanisms that regionalize its primordium in multiple independent histogenetic units. Rather than chaotic, this process is highly ordered, since it is fundamented on a hierarchic inherited Bauplan that is strongly conserved evolutionarily. The independent histogenetic units of the brain wall (composed of progenitors) obtain each a distinct genetic profile based on an unique combination of approximately hundred developmental genes (minimally). As a result, these units regulate individually developmental variables controlling growth (proliferation and patterns of neurogenesis) as well as differentiation of the neuronal daughter cells (neuronal typology and positioning in the brain, and their axonal navigation leading to sinaptogénesis). All this is previous to any functions, which will eventually appear once they are possible. Each areal histogenetic process is strictly causal and obeys the structural master plan (thats's why we invariably detect homologies when we compare the brains of diverse vertebrate species). Each unit creates just a small part of the whole edifice, and may collaborate in some other parts by contributing needed cells, or trophic factors, for instance. However, the enormous multiplicity of such units and the increment in complexity generated as progenitors produce vast amounts of neurons that interconnect one with another in complex arrays generates a gigantic amount of developing causal phenomena in a multilevel system of parts. This level of complexity makes it practically impossible to predict the final result. Nevertheless, a reasonable end result -a normal brain- obtains in most ontogenies. This situation corresponds to the "Ant's Country" described by Ian Stewart and Jack Cohen in "Figments of Reality. The Evolution of the Curious Mind" (Cambridge Univ. Press 1997). In Ant's Country unfathomable causal paths among numbers of paths that escape our calculation powers repeatedly lead finally to a recognizable result. I suppose that changes in brain evolution occur by emergence of novel routes across this complexly causal Ant's Country resulting from the diverse ontogenetic potencies. The evolved complex ontogenetic system is apparently highly canalized in the genome (insured from failure by many redundant gene actors) and it accordingly tends to produce once and again a brain capable of functioning, though it is practically impossible to discern the molecular and cellular details that cause an adaptative brain.