**Fig. 3.** Relationship between the expected number (*N*) of *V1R* ORFs left in a genome and the time (*T*) since pseudogenization started. The relationship is given by (see *Materials and Methods*), where *N*_{0} is the number of *V1R* genes in the genome before pseudogenization, and *t*_{1/2} is the half-life of a *V1R* gene under no functional constraints. Eight different values of *t*_{1/2} are considered, whereas *t*_{1/2} = 4.9 million years (MY) is our best estimate and is the one used in the main text. The actual number of ORFs left in humans today is *N* = 5, which is indicated by a horizontal dotted line. *N*_{0} is assumed to be 140 here. A different *N*_{0} will proportionally rescale the *y* axis. The upper and lower limits of the time since pseudogenization started are 35 and 23 MY, as indicated by two vertical dotted lines.