Clinical Neuroscience

[Evolution of human brain and intelligence]

LAKATOS László, JANKA Zoltán

JULY 30, 2008

Clinical Neuroscience - 2008;61(07-08)

[The biological evolution, including human evolution is mainly driven by environmental changes. Accidental genetic modifications and their innovative results make the successful adaptation possible. As we know the human evolution started 7-8 million years ago in the African savannah, where upright position and bipedalism were significantly advantageous. The main drive of improving manual actions and tool making could be to obtain more food. Our ancestor got more meat due to more successful hunting, resulting in more calory intake, more protein and essential fatty acid in the meal. The nervous system uses disproportionally high level of energy, so better quality of food was a basic condition for the evolution of huge human brain. The size of human brain was tripled during 3.5 million years, it increased from the average of 450 cm3 of Australopithecinae to the average of 1350 cm3 of Homo sapiens. A genetic change in the system controlling gene expression could happen about 200 000 years ago, which influenced the development of nervous system, the sensorimotor function and learning ability for motor processes. The appearence and stabilisation of FOXP2 gene structure as feature of modern man coincided with the first presence and quick spread of Homo sapiens on the whole Earth. This genetic modification made opportunity for human language, as the basis of abrupt evolution of human intelligence. The brain region being responsible for human language is the left planum temporale, which is much larger in left hemisphere. This shows the most typical human brain asymmetry. In this case the anatomical asymmetry means a clearly defined functional asymmetry as well, where the brain hemispheres act differently. The preference in using hands, the lateralised using of tools resulted in the brain asymmetry, which is the precondition of human language and intelligence. However, it cannot be held anymore, that only humans make tools, because our closest relatives, the chimpanzees are able not only to use, but also to make tools, and they can be tought how to produce quite difficult ones. Some brain characteristics connected to human consciousness and intelligence, like brain asymmetry, the “consciousness” or “theory of mind” based on mirror neurons are surprisingly present in monkeys. Nevertheless, the human intelligence is extremly flexible and different, while the animal intelligence is specialised, producing one thing at high level. Based on recent knowledge the level of intelligence is related anatomically to the number of cortical neurons and physiologically to the speed of conductivity of neural pathways, the latter being dependent on the degree of myelinisation. The improvement of cognitive functions including language is driver by the need of more effective communication requiring less energy, the need of social dominance, the competitive advantages within smaller groups and species or against other species, which improves the opportunity for obtaining food. Better mental skills give also sexual dominance, which is beneficial for stabilising “cleverness” genes. The evolutionary history of human consciousness emphasises its adaptive survival helping nature. The evolution of language was the basic condition of conscious thinking as a qualitative change, which fundamentally differentiate us from all other creatures.]

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