Flaws in evolutionary theory  and interpretation

We make three points. First, even if Finlay et al.'s proposed developmental mechanisms hold, there remains great scope for selection on specific brain structures. Second, the positive covariance among the size of brain structures provides far less support for the proposed developmental mechanisms than Finlay et al. acknowledge. Third, even if the proposed mechanisms are the primary size determinants for most brain structures, these structures should not be considered “spandrels.”

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The time when the “Tomte” of evolution was playing with time

Behavioral and Brain Sciences ◽

10.1017/s0140525x0131395x ◽

2001 ◽

Vol 24 (2) ◽

pp. 287-287

Author(s):

Giorgio M. Innocenti

Keyword(s):

Developmental Plasticity ◽

Brain Structures ◽

Developmental Constraints ◽

Developmental Mechanisms ◽

Differential Expansion ◽

High Degree ◽

Adaptive Role

Developmental constraints presumably had a major role in channeling evolution. In particular, developmental mechanisms may have coordinated the evolution of neocortex with that of other brain structures. However, the rules determining the differential expansion of different cortical territories remain to be determined as well as the adaptive role of cortical expansion versus that of the structures it is connected to. The high degree of developmental plasticity of neocortex was probably the key to its successful evolution.

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Concerted and mosaic evolution of functional modules in songbird brains

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2017.0469 ◽

2017 ◽

Vol 284 (1854) ◽

pp. 20170469 ◽

Cited By ~ 6

Author(s):

Jordan M. Moore ◽

Timothy J. DeVoogd

Keyword(s):

Size Composition ◽

Brain Structures ◽

Major Elements ◽

Neural Systems ◽

Brain Areas ◽

Functional Capabilities ◽

Developmental Mechanisms ◽

Mosaic Model ◽

Residual Variation ◽

Functional Capacities

Vertebrate brains differ in overall size, composition and functional capacities, but the evolutionary processes linking these traits are unclear. Two leading models offer opposing views: the concerted model ascribes major dimensions of covariation in brain structures to developmental events, whereas the mosaic model relates divergent structures to functional capabilities. The models are often cast as incompatible, but they must be unified to explain how adaptive changes in brain structure arise from pre-existing architectures and developmental mechanisms. Here we show that variation in the sizes of discrete neural systems in songbirds, a species-rich group exhibiting diverse behavioural and ecological specializations, supports major elements of both models. In accordance with the concerted model, most variation in nucleus volumes is shared across functional domains and allometry is related to developmental sequence. Per the mosaic model, residual variation in nucleus volumes is correlated within functional systems and predicts specific behavioural capabilities. These comparisons indicate that oscine brains evolved primarily as a coordinated whole but also experienced significant, independent modifications to dedicated systems from specific selection pressures. Finally, patterns of covariation between species and brain areas hint at underlying developmental mechanisms.

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Was the Ediacaran–Cambrian radiation a unique evolutionary event?

Paleobiology ◽

10.1017/pab.2014.2 ◽

2015 ◽

Vol 41 (1) ◽

pp. 1-15 ◽

Cited By ~ 17

Author(s):

Douglas H. Erwin

Keyword(s):

Evolutionary Theory ◽

Physical Environment ◽

Redox State ◽

Initial Conditions ◽

Ecological Interactions ◽

Developmental Mechanisms ◽

Evolutionary Event ◽

History Of ◽

Cambrian Radiation ◽

Sensitivity To Initial Conditions

AbstractThe extent of morphologic innovation during the Ediacaran–Cambrian diversification of animals was unique in the history of metazoan life. This episode was also associated with extensive changes in the redox state of the oceans, in the structure of benthic and pelagic marine ecosystems, in the nature of marine sediments, and in the complexity of developmental interactions in Eumetazoa. But did the phylogenetic and morphologic breadth of this episode simply reflect the unusual outcome of recurrent evolutionary processes, or was it the unique result of circumstances, whether in the physical environment, in developmental mechanisms, or in ecological interactions? To better characterize the uniqueness of the events, I distinguish among these components on the basis of the extent of sensitivity to initial conditions and unpredictability, which generates a matrix of possibilities from fully contingent to fully deterministic. Discriminating between these differences is important for informing debates over determinism versus the contingency in the history of life, for understanding the nature of evolutionary theory, and for interpreting historically unique events.

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The Reaction of Brain Structures with OsO4-Zinc-Iodide Stain

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100065419 ◽

1971 ◽

Vol 29 ◽

pp. 272-273

Author(s):

Werner J. Niklowitz

Keyword(s):

Electron Microscope ◽

Structural Changes ◽

Mossy Fiber ◽

Toxic Metal ◽

Staining Technique ◽

Brain Structures ◽

Oxidase Inhibitor ◽

Fiber Layer ◽

Hippocampal Tissue ◽

Zinc Iodide

After intoxication of rabbits with certain substances such as convulsant agents (3-acetylpyridine), centrally acting drugs (reserpine), or toxic metal compounds (tetraethyl lead) a significant observation by phase microscope is the loss of contrast of the hippocampal mossy fiber layer. It has been suggested that this alteration, as well as changes seen with the electron microscope in the hippocampal mossy fiber boutons, may be related to a loss of neurotransmitters. The purpose of these experiments was to apply the OsO4-zinc-iodide staining technique to the study of these structural changes since it has been suggested that OsO4-zinc-iodide stain reacts with neurotransmitters (acetylcholine, catecholamines).Domestic New Zealand rabbits (2.5 to 3 kg) were used. Hippocampal tissue was removed from normal and experimental animals treated with 3-acetylpyridine (antimetabolite of nicotinamide), reserpine (anti- hypertensive/tranquilizer), or iproniazid (antidepressant/monamine oxidase inhibitor). After fixation in glutaraldehyde hippocampal tissue was treated with OsO4-zinc-iodide stain and further processed for phase and electron microscope studies.

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