Trends in Genetics
Volume 17, Issue 12, 1 December 2001, Pages 697-701
Journal home page for Trends in Genetics

Opinion
A high density of X-linked genes for general cognitive ability: a run-away process shaping human evolution?

https://doi.org/10.1016/S0168-9525(01)02446-5Get rights and content

Abstract

The incidence of mental disability is 30% higher in males than in females. We have examined entries in the OMIM database that are associated with mental disability and for several other common defects. Our findings indicate that compared with the autosomes, the X chromosome contains a significantly higher number of genes that, when mutated, cause mental impairment. We propose that these genes are involved in the development of cognitive abilities and thus exert a large X-chromosome effect on general intelligence in humans. We discuss these conclusions with regard to the conservation of the vertebrate X-chromosomal linkage group and to human evolution.

Section snippets

Human X-chromosomal mental disability genes are evolutionarily conserved

In Table 3, we list non-syndromal MRX genes that, when mutated, lead to mental impairment as the only symptom. We propose that these genes have had a major impact on the rapid development of cognitive abilities during human evolution. As human beings, we are convinced that human evolution must be something special. Therefore, we are very interested to understand these ostensibly human-specific genes. However, as indicated in Table 3, organisms that are very distantly related to humans have

Female mate-choice has shaped the human mind

The observation of an excess of genes responsible for cognitive abilities on the X chromosome is reminiscent of an earlier observation that described an excess of sex- and reproduction-related genes on the human X chromosome 12. This phenomenon has been described as ‘the large X-chromosome effect’ 13, 14. We propose a large X-chromosome effect for general cognitive abilities in humans. It is reasonable to define the evolution of enhanced cognitive abilities as a specifically human trait. A

The brain and testis association

Many mental disability syndromes are associated with decreased fertility. In ten of the X-chromosomal syndromes listed in Table 1, reduced fertility or infertility is an additional symptom. We again performed X-chromosome- and autosome-specific queries of the OMIM database for entries containing both ‘mental retardation’ and symptoms influencing testis function (‘hypogonadism’ or ‘cryptorchidism'or ‘macroorchidism’). Interestingly, we found that entries matching these search criteria are about

The X chromosome in the evolution of vertebrate diversification and human cognitive abilities

Finally, there is a really surprising observation. The X chromosome has been in use as a sex chromosome for nearly 300 million years 11, and its gene content has been conserved 9, 10. However, evolution and speciation genetics revealed that the X chromosome was engaged in a dominant manner in the development of all characteristics that have been sexually selected for in the past 300 million years 19. Therefore, the most-conserved gene array was engaged in a dominant manner in the morphological

Acknowledgements

The ideas in this opinion paper were developed preparing lectures given at the retirements of Klaus Bender, Walther Traut, and Ulrich Wolf. Drs G. Assum and D. Kaufmann are thanked for fruitful discussions.

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