Evolutionary optimality in sex differences of longevity and athletic performances

Abstract

Many sexual differences are known in human and animals. It is well known that females are superior in longevity, while males in athletic performances. Even though some sexual differences are attributed to the evolutionary tradeoff between survival and reproduction, the aforementioned sex differences are difficult to explain by this tradeoff. Here we show that the evolutionary tradeoff occurs among three components: (1) viability, (2) competitive ability and (3) reproductive effort. The sexual differences in longevity and athletic performances are attributed to the tradeoff between viability (survival) and competitive ability that belongs to the physical makeup of an individual, but not related to the tradeoff between survival and reproduction. This provides a new perspective on sex differences in human and animals: females are superior in longevity and disease recovery, while males are superior in athletic performance.

Figure 1. Model of a sex-specific fitness tradeoff between viability, competitive ability and reproduction.

Assume the tradeoff among three components: viability v, competitive ability f and reproduction r, such that v + f + r = 1. We set c = 0.2 and n = 2, unless otherwise noted. (a,b) Fitness landscapes against v, f, and r. Because f = 1 – (v + r), f is automatically determined by the v-r plane, where 0 ≤ (v+r) ≤ 1 that corresponds 1 ≥ f ≥ 0. The open triangles indicates the optimal points (peaks). Three green lines in (a, b) corresponds (c–e). (a) Female fitness landscape, w_f = (v-c)fr = (v-0.2)fr. (b) Male fitness landscape, w_m = v f ⁿr = v f²r. (c) The tradeoff between v and f, assuming r = 0.3. (d) The tradeoff between r and f, assuming v = 0.5. (e) The tradeoff between v and r, assuming f = 0.2.

Figure 2. Examples of female superiority in humans and animals.

(a–d) Sexual difference of superiority in longevity. The sexual difference in longevity is measured by the value of (male longevity)/(female longevity). (a) The number of countries plotted against sexual difference in human longevity. (b) The number of species against sexual difference in longevity in 30 vertebrate species. (c) The number of species against sexual difference in longevity in 21 polygamous species. (d) The number of species against sexual difference in longevity in 9 monogamous species. (e) Sexual differences in human infant survival rate in six regions. The graphs show the values of (male infant survival)/(female infant survival). The survival rate of infant to reach age 1 is used for each region. Regions are Africa (Af), Americas (Am), South-East Asia (SEA), Europe (Eu), East Mediterranean (EM), and Western Pacific (WP). (f) Five-year survival rate of people suffering cancer after operation in Japan. Female survival rate is significantly larger than male survival rate (chi-square test: p = 0.0031). (g) 28-day survival rate of people suffering myocardial infarction after operation in Sweden. Female survival rate is significantly larger than male survival rate (chi-square test: p = 8.7 × 10⁻⁶). (a–d) The histogram of (male longevity)/(female longevity) is shown. (a–e) Male is superior if the difference > 1.00, while female is superior if the difference <1.00.

Figure 3. Examples of male superiority in competitive ability.

(a) The performance ratio between sexes in several world athletic records. The ratio of (male record)/(female record) is shown for 100 m running, marathon, 100 m freestyle swimming and 1500 m freestyle swimming. The ratio of (female record)/(male record) is used for hammer toss, because sexual superiority is reversed in this game. (b) Temporal changes in the performance ratios between sexes in the average juvenile (aged 12–19) in Japan. The ratio of (female record)/(male record) is used for all games except the 50 m dash for which the ratio of (male record)/(female record) is used to align the measure of sexual superiority. (c) The numbers of record holders for each sex in horse races. The turf and dirt courses are shown separately. (d) Male and female average heights in Japanese human populations between 13–25 years old. (e) Male and female average weights in Japanese human populations between 13–25 years old. (a,b) Female is superior if the performance ratio > 1.00, while male is superior if the performance ratio <1.00.