Gene number, noise reduction and biological complexity.

Preliminary estimates suggest that gene number, and hence biological complexity, increased suddenly at two periods of macroevolutionary change (the origin of eukaryotes and the origin of vertebrates), but otherwise remained relatively constant. As the genome is in constant flux, what normally constrains the number of different genes that an organism can retain? Here, I suggest that an important limitation on gene number is the efficiency of mechanisms that reduce transcriptional background noise. The appearance of both eukaryotes and vertebrates coincided with novel mechanisms of noise reduction.