ALT Top image - A timeline of the evolution of histones, their complexing with chromatin, and other known or hypothesised functions. Histone proteins are represented as blue spheres. Archaeal histones mostly lack N-terminal tails and form a looser chromatin structure, whereas compaction is increased in simple and higher eukaryotes. Lower image - Modes of chromatin release throughout the tree of life. The slime mould Dictyostelium discoideum releases chromatin via ETosis only while in a multicellular ‘slug’ phase. Plants release chromatin via root extracellular traps for defence against pathogens, whereas animal cells carry out ETosis in many contexts, such as immune or inflammatory responses or tissue repair.