[Cz-biology] Cannot save changes in Brain evolution

[postmaster at neurobiol.cyt.edu.ar]

Some mechanical problem does it, thus I'm saving the materials here. 

Summary of changes:  Evolution section had jumped from brain to psychological items; fixed; 
initial paragraph amended so as to consider brain evolution, not human brain evol. alone.
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== Brain Evolution	 ==

Like everything else in nature, the brain organ is a structure that has adapted over time – 
moving from the simple to the complex, sometimes back for special adaptations – to perform 
a variety of vital functions. At the same time, selection procedures took place, enhancing the 
functional capabilities of the CNS in accordance with the changing ecological needs. This 
also happened for humankind - along the paleoanthropological process of hominization - in 
accordance with its ecological and, possibly, its long-term cultural changes.

'''Vertebrate Brain Evolution'''

The classical view of telencephalic evolution proposes that the fish palaeostriatum is the 
antecedent of the human globus pallidus, the amphibian archistriatum is the antecedent of 
the human amygdala and the reptile neostriatum is the antecedent of the human caudate and 
putamen. Birds are thought to have unique additional basal ganglia, the hyperstriatum. 
Accordingly, the fish palaeocortex was thought to be the antecedent of the human olfactory 
cortex, the reptile archicortex to be the antecedent of the human hippocampus, while birds 
were proposed to have no further pallial regions. The neocortex was regarded as the unique 
and latest achievement of mammals. Since the 1960s and 1970s however, the classical view 
of brain evolution has been increasingly challenged. 

It is known that evolution is not linear, and thus one cannot assume that more recently 
evolved species are more advanced. According to the Avian Brain Nomenclature 
Consortium, the avian palaeostriatum augmentatum is homologous to the mammalian 
neostriatum, the avian palaeostriatum primitivum is homologous to the mammalian globus 
pallidus, and the avian hyperstriatum, neostriatum and archistriatum may be homologous to 
mammalial pallial regions. Moreover, recent findings suggest that mammals did not arise 
from reptiles, indicating that the reptilian nuclear pallial organisation cannot represent the 
ancestral conditions for mammals as was previously assumed. It is also known that 
telencephala of fish do not only contribute to olfactory functions and that fish have a 
hippocampus whose main function is not olfaction, but memory and spatial mapping. Overall, 
evidence indicates that there are pallial, striatal and pallidal structures in most or all 
vertebrates. It is apparent that the organisation of the basal ganglia amongst vertebrates is 
conserved, whereas the organisation of the pallial domains is more varied.

'''Evolution and Intelligence: What is different about the human brain?'''

A good measure of intelligence is ''“mental or behavioural flexibility resulting in the 
appearance of novel solutions that are not part of the animal’s normal repertoire”''. Among 
the many functions of the brain organ is the one of providing sensory imput for differentiating 
the set of mental contents, or "mind." Thus brains differ among species, as required to 
survive in species-specific ecological circumstances, or niches. The species-specific minds, 
built upon the sensory imput from the respective brain, operate under general psychological 
conditions and upon neural correlates, whose change results in the highest-level regulated 
behavior; but brain architectures also generate complex reflexes and kinesias (behavioral 
patterns, often involved in courtship and prey capture) without of before psychological 
involvement. It is unclear if the refinement of these abilities should be included in the global 
concept of a species' intelligence. Of all the proposed neural correlates of intelligence, 
general properties such as brain size, relative brain size, encephalization and prefrontal 
cortex are not the optimal predictors for intelligence. It is the number of cortical neurons 
combined with a high conduction velocity that correlates best with intelligence. Humans do 
not have the largest brain or cortex (either in absolute or relative terms) but have the largest 
number of neurons and perhaps the greatest information processing capacity. In addition, 
highly specialized structures in the human prefrontal cortex may also play an important role.

As intelligence has evolved in different classes, orders and families of vertebrates, it does not 
seem to have evolved in an orthogenetic way (i.e. that a single line culminates in Homo 
sapiens for example) but in a parallel way. Amongst vertebrates, humans are more intelligent 
than great apes, cetaceans and elephants, while these species are probably more intelligent 
than monkeys, and monkeys more intelligent than prosimians and the remaining animals. On 
the other hand, it is not clear whether humans have unique properties. Aspects of the most 
discussed human properties (tool use, tool-making, grammatical language, consciousness, 
self-awareness, imitation, deception and theory of mind) are also recognized in other non-
human primates and large-brained animals. Concerning the primate’s ability to learn 
languages, the existence of precursors to Wernicke’s and Broca’s areas in non-human 
primates is currently being discussed.

Overall, the outstanding intelligence of humans seems not to have resulted from qualitative 
differences, but rather from a combination and subsequent improvement of characteristics, 
including the theory of mind, language and consciousness.

'''Evolution at genetic and molecular level'''

Considering the great similarity between the chimpanzee and human genome,  evolutionary 
changes in anatomy are more likely based on changes in control mechanisms of gene 
expression rather than sequence changes in proteins. 

Apparently, mutations with greater pleiotropic effects are a less common source of variation 
due to their deleterious effects. Several genetic features (gene duplication, regulatory 
sequence expansion and diversification, and alternative protein isoform expression) increase 
variation and minimize pleiotropy associated with evolutionary mutations by contributing to 
compartmentation and redundancy. These mechanisms arise in coding sequences, whereas 
variation in promoter use or choice of splicing site arises in regulatory sequences. Several 
studies indicate that evolutionary mutations of regulatory sequences take place at loci 
encoding transcription factors or cis-regulatory elements. These evolutionary mutations are 
responsible for gain, loss or modification of morphological traits and provide a mechanism to 
change one trait while preserving the role of pleiotropic genes in other processes. There are 
some examples of evolutionary changes in anatomy due to gene duplication and mutation in 
coding sequences (for example changes in Hox-proteins being associated with shifts in form 
or development mechanisms). However, these events are relatively rare and may have 
accompanying deleterious pleiotropic effects, thereby limiting their contribution to evolution 
under natural selection.

Overall, both regulatory sequences and coding regions contribute to the evolution of 
anatomy, but it can be concluded that morphological evolution occurs primarily through 
changes in regulatory sequences. 

In contrast, there is ample evidence that changes arising in coding sequences play a crucial 
role in several important physiological differences between species. Regarding the synapse 
proteome, a great expansion of protein types due to gene family duplication and 
diversification has been revealed. Data suggests that most functional synaptic proteins were 
present in metazoans. This proto-synapse, with its pathways responding to environmental 
cues and performing simple cell-cell communication, has been elaborated on during the 
evolution of invertebrates and vertebrates. It is very likely that the increase in complexity in 
molecular signalling of vertebrates, along with neuron number and connectivity, contributes to 
their great behavioural capacity. Even small changes in components of synaptic signalling 
have a great multiplicative effect on neuronal function. Moreover, comparisons of synapse-
signalling complexes between ''Drosophila'' and mice indicate that additional species-specific 
adaptations of common synaptic subcomponents have diverged by duplication, recruitment 
and replacement of genes. Regional specialization with differential signal processing in 
mouse brains was also discovered. Different brain regions express a similar set of 
postsynaptic proteins, but in different combinations of expression levels. Recently-evolved 
genes encoding upstream molecules and structural components of signalling pathways seem 
to contribute most to diversity.



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