Reproductive overlap in humans and other primates. (*A*) Maximum reproductive versus maximum generational overlap in 12 primate species recently classed as exhibiting a postreproductive life span (). Maximum generational overlap, *G*, is defined as (MLS − AFB)/MLS, where AFB is average age at first birth and MLS is maximum recorded life span. Maximum reproductive overlap, *R*, is defined as (MRS − AFB)/MRS, where MRS is the maximum reproductive span, calculated as maximum age at last birth (MALB) minus AFB. For species without a postreproductive life span, in which MRS ≈ MLS, it would follow that *R* = 2 − (1/*G*). For our sample species (excluding humans), the least-squares linear regression of *R* on *G* is shown (*y* = −0.74 + 1.78*x*, *r*^{2} = 0.98). This regression would predict a MALB for humans of 70 years on the basis of generational overlap. We used MLS and MALB because these are the parameters typically reported in the literature. For four species (chimpanzees, orangutans, Japanese macaques, and humans), published data were sufficiently detailed to calculate mean reproductive overlap, defined as (ARS − AFB)/ARS, where ARS is the average (or mean) reproductive span (i.e., mean ALB minus AFB). (*B*) Pattern of overlap for these four species. For each species, horizontal bars represent the maximum life spans of three successive generations, scaled to a standard length and offset in accordance with the value of AFB relative to MLS, with mean reproductive spans shaded. The mean reproductive overlap values for Japanese macaques, orangutans, and chimpanzees were 0.71, 0.52, and 0.39, respectively, compared with a mean reproductive overlap for humans of 0.00. Values (in years) and reference sources used to plot the figure are as follows. Common chimpanzee (*Pan troglodytes*): MLS = 47, AFB = 14.7, MALB = 43.8 [means of Mahale/Tai/Bossou/Gombe populations (–, –)]), mean ALB = 38.9 (mean of Mahale/Tai/Gombe values for females that survived to the MALB of their respective populations). Gorilla (*Gorilla gorilla*): MLS = 35, AFB = 10, MALB = 30 (, ). Orangutan (*Pongo pygmaeus*): MLS = 44, AFB = 12.3, MALB = 41; mean ALB = 38 (). Human (*Homo sapiens*): MLS = 82.5, AFB = 19.1, MALB = 47 [Ache/!Kung mean values (, )], mean ALB = 38.2 [mean for Ache/!Kung females surviving to age 50 (, )]. Olive baboon (*Papio cynocephalus anubis*): MLS = 27, AFB = 6, MALB = 25 (). Japanese macaque (*Macaca fuscata*): MLS = 32.7, AFB = 5, MALB = 25.4 (), mean ALB = 22.5 [mean for females surviving to MALB ()]. Barbary macaque (*Macaca sylvanus*): MLS = 28, AFB = 4, MALB = 23 (). Pig-tailed macaque (*Macaca nemestrina*): MLS = 28, ALB = 22, AFB = 5 (). Rhesus macaque (*Macaca mulatto*): MLS = 19, MALB = 18 (), AFB = 2.6 (). Hanuman langur (*Presbytis entellus*): MLS = 35, AFB = 4, MALB = 32 (). Tamarins (*Sanguinus* spp. (2 spp.): MLS = 20, MALB = 17 (), AFB = 2 (). Mouse lemur (*Microcebus murinus*): MLS = 14, MALB = 11 (), AFB = 0.95 ().

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