Infanticide Is No Fallacy

The American Anthropologist recently published a critique by Anne Innis Dagg (1998) claiming to refute a series of scientific publications on infanticide in male African lions. Joan Silk and Craig Stanford (1999) rebutted Dagg's paper, providing a concise summary of prior work on this topic. In brief, Bertram (1975), Packer and Pusey (1984; Pusey and Packer 1994) showed that cub mortality increases dramatically when new males first join a pride. Although incoming males have only occasionally been seen to kill cubs, direct observations are difficult to obtain and most of the mortality has been inferred from demographic records. Mothers quickly return to estrus after losing their dependent offspring and then mate with the incoming males. Infanticidal behavior thus accelerates the males' opportunity to father their own offspring. This pattern is consistent with the hypothesis first articulated by Sarah Hrdy (1974) concerning the adaptive significance of infanticide by incoming males. Dagg (2000) has written a rejoinder to Silk and Stanford that repeats many of her original assertions. First, she claims that infanticide is not as common as generally believed, basing her reply on an apparent discrepancy between the observations of George Schaller (1972) and all subsequent observers in the Serengeti. Schaller provided the first comprehensive description of lion biology and natural history, and his book was certainly a landmark in its time. However, Schaller's study only lasted 3.25 years, and it preceded the great infusion of evolutionary theory into the behavioral sciences in the mid-1970s. So it is not surprising that many of his ideas and interpretations have been superseded. For example, Schaller tabulated the foraging success of different-sized hunting groups, and numerous "armchair" lion ecologists later used his data to predict the optimal group size of hunting lions. These data proved inadequate to test such detailed predictions, and further field studies came to very different conclusions (Packer et al. 1990). This is not to say that Schaller was wrong or unreliable; he just hadn't collected an appropriate dataset to test the hypotheses that his initial observations had inspired. Many of Schaller's ideas about lion social behavior have stood the test of time. Lion prides are certainly fission-fusion social groups; male coalitions enter the pride from elsewhere; daughters may be recruited into their mothers' pride. However, some of his conclusions were misleading. For example, he categorized lions as either "residents" or "nomads," implying that while most animals were sedentary, a proportion of the population wandered permanently over the Serengeti. We now know that most "nomads" only wander temporarily: they are either dispersing subadults or males who have lost residence in a pride. Schaller's comments about nomads were not wrong, they were incomplete; he only watched lions for a few years. Without long-term records, he couldn't have seen the larger pattern. Similarly, there was no way that he could have appreciated the larger pattern of infanticide. Although Schaller monitored over a dozen prides, most of his observations were based on only two prides, the Masai Pride and the Seronera Pride. As it happened, his observations of the Masai Pride coincided with a long period of social stability-the original breeding coalition maintained residence until August of 1969 (when Schaller was busy preparing to leave the Serengeti), and Brian Bertram witnessed the first recorded takeover of this pride. A new set of males briefly entered the Seronera Pride in September 1967, and a second coalition established long-term residence in December 1967. The Seronera Pride suffered considerable cub mortality over these months, including three cubs killed by the second coalition (p. 49 of Schaller's book). However, since Schaller saw no reason to pay special attention to male takeovers, he was in no position to comment on the frequency of infanticide in this context.