LETTER

Evolution of social in is not consistently associated with male

Comparative analyses suggest that monoga- and phylogeny, which indicates that the con- occur consistently over evolutionary time, but mous breeding systems evolved in trast between the results of the two analyses only once conditions pass a threshold (5). where feeding competition reduces range is unlikely to result from these differences. Our results indicate that models of evolution overlap between breeding females, preventing One possible explanation for the contrasting that do not assume constant change explain males from guarding more than one female results of Opie et al. is that their analyses transitions in infanticide better, and these at a time (1). In contrast, a recent analysis for underestimated the frequency of male infan- reconstructions provide no support for the primates suggests that monogamy evolved as ticide by classifying many polygynous suggestion that the distribution of male in- a form of paternal care that reduces the risk as not showing male infanticide on the basis fanticide exerted an important influence on of male infanticide (2). Here we reexamine of insufficient evidence. Opie et al. address the distribution of monogamy in primates the dilemma of deciding when the absence the evolution of monogamy either in pri- and attempt to explain the contrasting re- of observations of infanticide is sufficient to mates or in other mammals. sults of the two analyses. Methods and de- conclude that it does not occur by only in- Dieter Lukas1 and Tim Clutton-Brock tailed results are described in supplementary cluding species for which at least 20 scientific material (3). studies have been published. However, for Department of Zoology, University of Our analyses of data for primates provide several of the species included, the majority Cambridge, Cambridge CB2 3EJ, no evidence that the evolution of monogamy of publications are medical reports on captive United Kingdom in primates follows a different pattern from animals where experimental conditions limit the evolution of monogamy in other mam- any possibility of male infanticide. Even mals. Our results suggest the following: (i) when animals are studied in natural popula- 1 Lukas D, Clutton-Brock TH (2013) The evolution of social monogamy in mammals. Science 341(6145):526–530. evolutionary transitions to social monogamy tions, rare events like male infanticide may 2 Opie C, Atkinson QD, Dunbar RIM, Shultz S (2013) Male in primates are associated with reductions in not be observed for several years (4). The infanticide leads to social monogamy in primates. Proc Natl Acad Sci home range overlap, indicating that they inclusion of a large sample of polygynous USA 110(33):13328–13332. 3 Lukas D, Clutton-Brock T (2014) Data from: Evolution of social are associated with increased competition species classified as not having infanticide monogamy in primates is not consistently associated with male between females; and (ii) the ancestral con- could have biased the Bayesian inference infanticide. Available at http://doi.org/10.5061/dryad.hc967. dition for transitions to monogamy is as- and led to the conclusion that transitions to Accessed March 17, 2014. 4 sociated with decreased risks of infanticide and from infanticide are relatively uncom- Borries C, Savini T, Koenig A (2011) Social monogamy and the threat of infanticide in larger mammals. Behav Ecol Sociobiol 65(4):685–693. compared with ancestors that remained mon in polygynous species, and this may, 5 Felsenstein J (2012) A comparative method for both discrete and polygynous rather than increased risks. Phy- in turn, have caused the model to infer that continuous characters using the threshold model. Am Nat 179(2): logenetic reconstructions suggest that monog- changes in infanticide are associated with 145–156. amyislikelytohaveevolvedfromancestors monogamy. The Bayesian inference may in which males did not commit infanticide. have been further biased by Opie et al.’s Author contributions: D.L. and T.C.-B. wrote the paper. We repeated our analyses classifying the choice of the Brownian motion model to re- The authors declare no conflict of interest. social system of species on the basis of Opie flect evolutionary transitions in infanticide. 1To whom correspondence should be addressed. E-mail: dl384@ et al.’s criteria and relying on their method Changes in binary traits are not expected to cam.ac.uk.

E1674 | PNAS | April 29, 2014 | vol. 111 | no. 17 www.pnas.org/cgi/doi/10.1073/pnas.1401012111 Downloaded by guest on September 30, 2021