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Defining genetic variability of brain structure paired with brain plasticity as key factors of Homo sapiens species evolutionary success  

This project is open for collaborative development.  

I. Basic hypotheses  

The project postulates that genetically determined variability of brain structure within the human population determines the observed variability of linguistic, logical, social and artistic abilities within individual human beings. The postulate is thus embedded in the theory of multiple intelligences proposed by Howard Gardner (Gardner, Howard, 1993, Frames of mind: The theory of multiple intelligences. New York: Basic Books).  

The project assumes that brain plasticity, i.e. a feature of the young human brain to organize its structure by interaction with the multiple sensory inputs during infancy in order to develop the neuronal basis for most higher cognitive abilities, modifies brain structure and function to a certain extend enabling different human brain structures to perform most intellectual tasks sufficiently effectively.

It is generally accepted that genetic contribution towards the variability of cognitive brain function exceeds environmental influence (Wright et al. Genetics of cognition: outline of a collaborative twin study. Twin Res. 2001, 4:48-56).
Likewise, one may assume that genetic contribution towards the variability of brain structure exceeds the influence of brain plasticity.

The project finally hypothesizes that a high degree of genetic variability of the brain structure exists within the human population and that this high degree of genetic variability represents a key factor of Homo sapiens species evolutionary success.
This hypothesis is yet unproven. Genetically determined lateralization of brain functions such as functional lateralization of language as well as right-left handedness may be an argument in favour of this hypothesis. A putative gene of handedness has been identified (Francks et al. LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia. Mol Psychiatry. 2007;12:1129-39). The percentage of left-handedness seems to be rather stable within different human populations and over time (Llaurens et al. Why are some people left-handed? An evolutionary perspective. Philos Trans R Soc Lond B Biol Sci. 2008 Dec 5) suggesting an evolutionary advantage of conserving this genetic polymorphism. The development of handedness itself has been proposed as a principal evolutionary event enhancing the cognitive functions of Homo sapiens ancestors (Crow TJ. The 'big bang' theory of the origin of psychosis and the faculty of language. Schizophr Res. 2008;102:31-52) although handedness can also be found in great apes (Cantalupo et al. Handedness for tool use correlates with cerebellar asymmetries in chimpanzees (Pan troglodytes). Behav Neurosci. 2008;122:191-8). For attention deficit/hyperactivity disorder (ADHD), it has also been postulated that positive evolutionary selection of an associated polymorphism might be linked to enhanced reproductive fitness or to the general evolutionary benefit of genetic heterogeneity (Williams J, Taylor E. The evolution of hyperactivity, impulsivity and cognitive diversity. J R Soc Interface. 2006;3:399-413).

The hypotheses further assumes that the evolutionary advantage of a human population with a high degree of genetic variability of brain structure and subsequent variability of cognitive abilities might result from preadaptation as well as from the division of labor in human societies.

Preconditions for the evolutionary advantage of a high degree of genetic variability of brain structure are language and altruism. Language enables propagation of scientific and cultural innovations invented by intellectually more specialized and able individuals towards less specialized individuals within a social group enhancing the overall evolutionary fitness of the social group. Altruism within a social group allows survival of intellectually more specialized but possibly less viable individuals and thus preserves genetic heterogeneity.