Protein length distribution is generally consistent across species, according to a new analysis in Genome Biology. Researchers from the University of Lausanne in Switzerland and elsewhere compare the lengths of proteins from more than 2,300 species, including nearly 1,700 bacteria, 153 archaea, and 485 eukaryotes. They note that proteins from bacteria and archaea tend to be smaller, 270 amino acids and 242 amino acids, respectively, than eukaryotic proteins, which are 353 amino acids in length on average. The variation in protein length is also lower among bacterial and archaeal species. But comparing across a subset of representative proteomes, the researchers note that the protein length distributions of species overlap. Further, this variation in distribution was low in comparison to variation in other features such as genome size, gene length, and protein number. "[P]rotein length distribution is a remarkably consistent feature across species," they write. "This finding stands in stark contrast to other genomic features and suggests that protein length may be subject to unique evolutionary constraints."