The evolution of monogamy in response to partner scarcity - PubMed (original) (raw)

The evolution of monogamy in response to partner scarcity

Ryan Schacht et al. Sci Rep. 2016.

Abstract

The evolution of monogamy and paternal care in humans is often argued to have resulted from the needs of our expensive offspring. Recent research challenges this claim, however, contending that promiscuous male competitors and the risk of cuckoldry limit the scope for the evolution of male investment. So how did monogamy first evolve? Links between mating strategies and partner availability may offer resolution. While studies of sex roles commonly assume that optimal mating rates for males are higher, fitness payoffs to monogamy and the maintenance of a single partner can be greater when partners are rare. Thus, partner availability is increasingly recognized as a key variable structuring mating behavior. To apply these recent insights to human evolution, we model three male strategies - multiple mating, mate guarding and paternal care - in response to partner availability. Under assumed ancestral human conditions, we find that male mate guarding, rather than paternal care, drives the evolution of monogamy, as it secures a partner and ensures paternity certainty in the face of more promiscuous competitors. Accordingly, we argue that while paternal investment may be common across human societies, current patterns should not be confused with the reason pairing first evolved.

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Figures

Figure 1

Figure 1. Schematic of the model with all strategies represented.

Squares encompass females paired with either Mate Guarding (MG) or Parental Care (PC) males, with MG-paired females leaving the mating pool each time step. Females not in squares have paternity shared among Multiple Mating (MM) males. The dotted arrow represents some paternity given to MM males through cuckoldry.

Figure 2

Figure 2. Evolutionary dynamics of the three male mating strategies under a female-biased sex ratio.

The panels present six conditions with varying cuckoldry risk and payoffs to parental care (a–f) where conception rate (b) is set to 0.3. Colors denote which strategy is favored at a given strategy frequency, with yellow indicating Mate Guarding (MG), red Multiple Mating (MM), and blue Paternal Care (PC). Arrows simulate evolutionary trajectories at contrasting mixed-strategy frequencies. Color combination purple indicates when both MM and PC strategies are simultaneously increasing in frequency.

Figure 3

Figure 3. Evolutionary dynamics of the three male mating strategies under a male-biased sex ratio.

The panels present six conditions with varying cuckoldry risk and payoffs to parental care (a–f) where conception rate (b) is set to 0.3. Colors denote which strategy is favored at a given strategy frequency, with yellow indicating Mate Guarding (MG), red Multiple Mating (MM), and blue Paternal Care (PC). Arrows simulate evolutionary trajectories at contrasting mixed-strategy frequencies. Color combination yellow-blue indicates when both MG and PC strategies are simultaneously increasing in frequency.

Figure 4

Figure 4. Effects of ASR on equilibrium frequencies of Parental Care (PC), Mate Guarding (MG), and Multiple Mating (MM) strategies when MM is initially common.

The four panels (a–d) present four conditions with varying levels of parental care and cuckoldry rates. In all simulations the MM strategy is initially common at frequency 0.99, with MG and PC strategies at 0.005. Other parameter values are b = 0.3 and u = 0.9. See model description for details.

References

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