Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.
"An abbreviation of the prepubertal growth period by some 4 years might have had a parallel effect on brain development. ... There is a relation between age at puberty and body build. Early maturers tend to be broad-built pyknic (most "feminine" or "masculine"), while late maturers are of a more linear leptosomic (androgynous) build (Marchall & Tanner 1986). There is also a relation between body build and mental illness. Pyknic body build predominates (90%) in classical manic-depressive psychosis (MDP) and leptosomic-dysplastic body build (80%) in schizophrenia (S) (Kretschmer 1921, 1961). In comparison, only around 20% of the general population were of true pyknic or leptosomic build. It is suggested that MDP is a disorder affecting very maturers (early puberty) and S affects extremely late maturing individuals (late puberty). From the secular trends of 4 years' decline in mean pubertal age, we would expect an increase in MDP and a decline in S. The National Norwegian Case Register comprises all first admissions to psychiatric hospitals and clinics by diagnosis since 1916 (Odegard 1971, Saugstad & Odegard 1980, 1983, 1985, 1986). Between 1926 and 1965, there was a more than 50% increase in first admissions classified as MDP or reactive depression psychosis (ICD 298.0). A majority of the latter is diagnosed as MDP on readmission. Practically all the increase occurred after 1955, when in addition as increasing proportion of MDP was being classified as non-psychotic. Non-psychotic depressions (300.4) increased from less than 5% before 1040 to above 10% in the sixties, and to over 20% by 1978. Many of these patients are certified, being considered psychotic. We seem therefore justified in stating that there has been a marked rise in MDP during the last 30 years in Norway." (Saugstad, L.F. (1989) Mental illness and cognition in relation to age at puberty: a hypothesis. Clinical Genetics 36 (3): pp. 157)
"Onset of puberty is usually considered to coincide with the last major step in brain development: the elimination of some 40% of neuronal synapses. Mean pubertal age has declined by some 4 years during the last 100 years. There is a relation between age at puberty and body build, and between body build and mental illness. The difference in body build between schizophrenia (S) and manic-depressive psychosis (MDP) is similar to that between late and early maturers. It is suggested that S affects late-maturing individuals and MDP very early maturers. The observed marked rise in MDP and decline in the most malignant forms of S (non-paranoid) are in agreement with MDP and S as neurodevelopmental disorders occurring at the extremes of maturation. Maturational irregularities are most likely to occur at the extremes, and it is suggested that abbreviation of the regressive process may have led to persistent redundancy of neuronal synapses in MDP and that prolongation of the process past the optimal has yielded an inadequate synaptic density in S. The lack of cerebral abnormality in the majority of MDP and the presence of only subtle structural deficits in S, are in agreement with this. The two disorders are probably as old as mankind, and early puberty is the necessary factor for the development of MDP and late puberty is the necessary factor for that of S. There is an inverse relation between spatial ability and rate of maturation, whereas verbal ability is unaffected by maturational rate. From a previous predominance in both sexes, spatial ability (Performance IQ scores) has been reduced to below verbal ability (Verbal IQ scores) in the female sex and in early maturing males." (Saugstad LF (1989) Mental illness and cognition in relation to age at puberty: a hypothesis. Clin Genet 36(3):156)