Evolution of the brain
One approach to understanding overall brain evolution is to use a paleoarchaeological timeline to trace the necessity for ever increasing complexity in structures that allow for chemical and electrical signaling.
[6] Another approach to understanding brain evolution is to look at extant organisms that do not possess complex nervous systems, comparing anatomical features that allow for chemical or electrical messaging.
Ctenophores also demonstrate this crude precursor to a brain or centralized nervous system, however they phylogenetically diverged before the phylum Porifera (the Sponges) and Cnidaria.
[8] A trend in brain evolution according to a study done with mice, chickens, monkeys and apes concluded that more evolved species tend to preserve the structures responsible for basic behaviors.
The purpose of this part of the brain is to sustain fundamental homeostatic functions, which are self regulating processes organisms use to help their bodies adapt.
A key feature of cortex is that because it scales with surface area, more of it can be fit inside a skull by introducing convolutions, in much the same way that a dinner napkin can be stuffed into a glass by wadding it up.
The development of these recent evolutionary changes in the neocortex likely occurred as a result of new neural network formations and positive selections of certain genetic components.
Studying the brain's development at various embryonic stages across differing species provides additional insight into what evolutionary changes may have historically occurred.
argue that this difference is due to vertebrate and cephalopod neurons having evolved ways of communicating that overcome the scalability problem of neural networks while most animal groups have not.
They argue that the reason why traditional neural networks fail to improve their function when they scale up is because filtering based on previously known probabilities cause self-fulfilling prophecy-like biases that create false statistical evidence giving a completely false worldview and that randomized access can overcome this problem and allow brains to be scaled up to more discriminating conditioned reflexes at larger brains that lead to new worldview forming abilities at certain thresholds.
This means when neurons scale in a non randomized fashion that their functionality becomes more limited due to their neural networks being unable to process more complex systems without the exposure to new formations.
Different sizes in the cortical areas can show specific adaptations, functional specializations and evolutionary events that were changes in how the hominoid brain is organized.
Using the models for neurological reorganization it can be suggested the cause for this period, dubbed middle childhood, is most likely for enhanced foraging abilities in varying seasonal environments.
The new genes expressed during human neurogenesis are notably associated with the NOTCH, WNT and mTOR pathways, but are also involved ZEB2, PDGFD and its receptor PDGFRβ.
[15] Bruce Lahn, the senior author at the Howard Hughes Medical Center at the University of Chicago and colleagues have suggested that there are specific genes that control the size of the human brain.
The researchers at the University of Chicago were able to determine that under the pressures of selection, both of these genes showed significant DNA sequence changes.
Lahn's earlier studies displayed that Microcephalin experienced rapid evolution along the primate lineage which eventually led to the emergence of Homo sapiens.
The changes in DNA sequences of these genes accumulated to bring about a competitive advantage and higher fitness that humans possess in relation to other primates.
This comparative advantage is coupled with a larger brain size which ultimately allows the human mind to have a higher cognitive awareness.
[27] A hominid-specific duplicated gene, LRRC37B, codes for a transmembrane receptor that is selectively localized at the axon initial segment of human cortical pyramidal neurons.
DNA repair tends to occur preferentially at evolutionarily conserved sites that are specifically involved with the regulation of expression of genes essential for neuronal identity and function.
Endocasts occur when, during the fossilization process, the brain deteriorates away, leaving a space that is filled by surrounding sedimentary material over time.
[52] However, recent research has called into question the hypothesis of a threefold increase in brain size when comparing Homo sapiens with Australopithecus and chimpanzees.
[50] Progressing along the human ancestral timeline, brain size continues to steadily increase (see Homininae) when moving into the era of Homo.
In 2021, scientists suggested that the brains of early Homo from Africa and Dmanisi, Georgia, Western Asia "retained a great ape-like structure of the frontal lobe" for far longer than previously thought – until about 1.5 million years ago.
[69] This three-layer cortex is still conserved in some parts of the human brain such as the hippocampus and is believed to have evolved in mammals to the neocortex during the transition between the Triassic and Jurassic periods.
[71] Across species of mammals, primates have greater neuronal density compared to rodents of similar brain mass and this may account for increased intelligence.
[68] Explanations of the rapid evolution and exceptional size of the human brain can be classified into five groups: instrumental, social, environmental, dietary, and anatomo-physiological.
[74] The dietary theories maintain that food quality and certain nutritional components directly contributed to the brain growth in the Homo genus.
[75] The anatomo-physiologic concepts, such as cranio-cerebral vascular hypertension due to head-down posture of the anthropoid fetus during pregnancy, are primarily focused on anatomic-functional changes that predispose to brain enlargement.
