Fig. 4: Distribution of the age of human gene functions.

Most human gene functions evolved from very distant ancestors. a, Distribution of the time periods at which human genes evolved their present-day functions as assessed using two measures: the overall function of a gene (black bars, considering all functional characteristics) and the oldest functional characteristic of a gene (grey bars). Black bars indicate the most recent (newest) functional characteristic to arise in the evolutionary model for that gene, whereas grey bars indicate the age of the most ancient (oldest) functional characteristic among all the functional characteristics for that gene. As shown in Fig. 1, each evolutionary event in our models is mapped to a branch of a gene tree, which represents a period of time separating the LCAs of two different taxonomic groups; the evolution of each functional characteristic is assigned to the corresponding time interval (see Methods for details). As an additional reference, LCAs are expressed in more commonly recognized terms towards the right side. b, Age distributions for different types of human gene functions; each time interval is shaded according to the fraction of genes that evolved a given functional type during that interval. Different types of functions display substantially different age distributions, with some basic cellular metabolic functions in humans having remained largely unchanged over billions of years, whereas other groups, such as regulation of transcription and immune processes, have undergone substantial recent evolutionary change. Higher-level functional types are indicated in bold, with more specific subtype names indented below. Taxonomic names are from NCBI Taxonomy⁵³, except Amorphea, the group that includes the Amoebozoa and Opisthokonta (fungi and animals). Note that different functional characteristics of the same gene may have evolved at different times. Ma, millions of years ago.