PT  - JOURNAL ARTICLE
AU  - Eric Lewitus
AU  - Iva Kelava
AU  - Alex T. Kalinka
AU  - Pavel Tomancak
AU  - Wieland B Huttner
TI  - An Adaptive Threshold in Mammalian Neocortical Evolution
AID  - 10.1101/001289
DP  - 2013 Jan 01
TA  - bioRxiv
PG  - 001289
4099  - http://biorxiv.org/content/early/2013/12/16/001289.short
4100  - http://biorxiv.org/content/early/2013/12/16/001289.full
AB  - Expansion of the neocortex is a hallmark of human evolution. However, it remains an open question what adaptive mechanisms facilitated its expansion. Here we show, using gyrencephaly index (GI) and other physiological and life-history data for 102 mammalian species, that gyrencephaly is an ancestral mammalian trait. We provide evidence that the evolution of a highly folded neocortex, as observed in humans, requires the traversal of a threshold of ∼109 neurons, and that species above and below the threshold exhibit a bimodal distribution of physiological and life-history traits, establishing two phenotypic groups. We identify, using discrete mathematical models, proliferative divisions of pro-genitors in the basal compartment of the developing neocortex as evolutionarily necessary and sufficient for generating a fourteen-fold increase in daily prenatal neuron production and thus traversal of the neuronal threshold. Finally, using RNA-seq data from fetal human neocortical germinal zones, we show a genomic correlate to the neuron threshold in the differential conservation of long intergenic non-coding RNA. (see arXiv:1304.5412)