"ASPM" is an acronym for "Abnormal Spindle-like, Microcephaly-associated", which reflects its being an ortholog to the Drosophila melanogaster "abnormal spindle" (asp) gene. ASPM is located on chromosome 1, band q31 (1q31).
The mouse gene, Aspm, is expressed in the primary sites of prenatal cerebral cortical neurogenesis. The difference between Aspm and ASPM is a single, large insertion coding for so-called IQ domains.
The mean estimated age of the ASPM allele of 5,800 years ago, roughly correlates with the development of written language, spread of agriculture and development of cities. Currently, two alleles of this gene exist: the older (pre-5,800 years ago) and the newer (post-5,800 years ago). About 10% of humans have two copies of the new ASPM allele, while about 50% have two copies of the old allele. The other 40% of humans have one copy of each. Of those with an instance of the new allele, 50% of them are an identical copy suggesting a highly rapid spread from the original mutation. According to a hypothesis called a "selective sweep", the rapid spread of a mutation (such as the new ASPM) through the population indicates that the mutation is somehow advantageous to the individual. As of today, there is no evidence to support the notion that the new ASPM allele increases intelligence, and some researchers dispute whether the spread of the allele even demonstrates selection. They suggest that the current distribution of the alleles could be explained by a founder effect, following an out of Africa dispersal. However, statistical analysis has shown that the older forms of the gene are found more heavily in populations that speak tonal languages like Chinese.