Term Paper on "Infanticide in the Animal Kingdom"

Term Paper 5 pages (1623 words) Sources: 1

[EXCERPT] . . . .

Infanticide in the animal kingdom, particularly among primates, has become an issue of increased study and controversy. In general, there are two ways of looking at the phenomenon from an anthropological perspective; the killing of infants by unrelated males may be a reproductive strategy practiced by males of many species, or it may simply be a pathological behavior that has arisen independently of any evolutionary consequences. From the biologist's point-of-view, the first way of understanding male infanticide is by far the most compelling way to interpret it. After all, it makes sense within the context of the evolutionary arms race between the sexes that males should seek to eliminate the reproductive impact of their sexual competitors in any way that they can. Of course, this overall goal can manifest itself in direct physical competition with other males, specialized reproductive organs which can remove the fertilization material of other males from females, sexual dimorphism in the form of size and strength advantages, and, perhaps, even infanticide. From this standpoint, the case for infanticide as a reproductive strategy is a strong one, and provides interesting insights into the behaviors of other primate species, especially humans.

The act of infanticide is defined as "any behavior that makes a direct and significant contribution to the immediate death of an embryo or newly hatched born member of the perpetrator's own species," (Janson 1). If viewed as a behavior which has evolved as a successful way for the perpetrator to increase their overall sexual fitness, its ultimate cause may stem from one or more of the following potential advantages: increased resources acquisition, the elimination of competitors, increased fitness in one or both parents, increase reproductive success of the perpetrators (Janson 1). These all stand as goals that any male automatically seeks within the confines of evolution. After all, one of the most basic rules of animal biology is that, relatively speaking, sperm is cheap while eggs are expensive. In other words, the males of any given species typically do not invest very much in the reproductive process, while the female invests a substantial amount of time and energy. The female must be responsible for, at a minimum, the time and energy associated with gestation; also, among primates, the female is responsible for caring for the infant for months or even years after birth, which involves more energy from food and milk. Meanwhile, males are less directly involved in providing for the young. Accordingly, it is within their best interest to mate with as many females as possible, because the only energy they are required to donate is the minimal amount associated with sexual activity.

This situation has resulted in what has been termed the "arms race" between the sexes; while males seek reproductive strategies that increase their ability to mate with the most females, the females seek reproductive strategies that enable them to be more selective in their mating choices. So, the limiting factor in most males' reproductive strategies is access to mates, while females are limited by the resources that enable them to either produce the most offspring or the most successful offspring (Janson 2). Consequently, the arms race centers upon females seeking ways to express their preferences for particular mates, and males seeking ways to mate with those females who do not prefer them (Janson 2). One of the many results of this situation is that males compete both directly and indirectly with other males. So it therefore becomes feasible that infanticide is a reasonable course of action for males who do not want -- evolutionarily speaking -- their potential mates wasting all of their energy raising infants unrelated to them.

Females are vulnerable to this tactic both because their infants are fragile, requiring almost constant care, and because sexual dimorphism within primates has favored males who are larger and stronger than their female counterparts. This means that should a male choose to do so, he is likely capable of overpowering any particular female and killing her offspring with relatively little difficulty: "The bigger a male is relative to a female, the easier it may be for him to challenge her and gain possession of her infant," (Janson 479). The additional result of this physical difference between the sexes is that the males are then often capable of mating with these females without their willing consent. Since infants in the primate world are typically highly dependent upon their mother for some time, the risk associated with infanticide is relatively high as well. Ultimately, within primates, this risk must be counterbalanced with the advantages of parental care of offspring incapable of surviving on their own -- cognitive development, learning, and growth rates. Yet in general, the longer an infant is dependent upon its mother, the greater the risk of male-perpetrated infanticide.

Determining the factors which most strongly influence the rate at which infants are killed by males within any given population, however, is fairly complex. Since different species have different reproductive rates and different social organizations, it is not altogether clear which feature of an animal's behavior can be identified as the proximate cause. Nevertheless, as Janson and Van Schaik argue, one of the determining factors seems to be the "relative male replacement rate" -- or RMRR -- within any given population (Janson 478). This is a measure of the rate of which the dominant male within a group is replaced by another, new dominant male. Research has suggested that among many species, the highest rates of infanticide occur during the period immediately following the arrival of a new dominant male. Thus, it should not be surprising that the most often dominancy changes hands within a population of primates, the higher the risk of infanticide. Of course, this factor is acted upon by a number of others which make is somewhat variable. Nevertheless, "RMRR is positively correlated with infanticide rate, albeit weakly," (Janson 478). Ultimately, this is because although it may be a proximate factor, it is by no means the definitive factor by virtue of the many different types of social organizations which witness some form of infanticide.

Janson and Van Schaik offer a handful of examples of female counterstrategies to combat high rates of infanticide. Three of these include: association with a male capable of protecting her from infanticidal males; confused paternity; and social defense from groups of females (Janson 487). All of these are particularly interesting strategies because they can be seen across different species and have a number of corollaries among human populations. The first is somewhat significant, because association with a particular male may be beneficial to the female and the male alike. If the male happens to be a sibling of the female, protecting her offspring may be menially beneficial to him from an evolutionary standpoint, because it makes his parent's genetic material potentially more competitive. Furthermore, it may be beneficial for younger males to behave in this manner, because if they ever are ever later provided with the opportunity to reproduce the risk to their offspring will be reduced by social ties. Confused paternity is also a powerful force in reducing the risk of infanticide within populations where multiple males mate with multiple females. In this way, a potentially infanticidal male may not kill off his competitor's offspring because he cannot distinguish between them and his own. From this point-of-view, females that preferentially seek-out groups with multiple mating males automatically reduce their risk of infanticide. Social defense can also come from groups of females. Although this may be rarer among primates, it is obvious that several females could potentially protect their vulnerable offspring from one aggressive male. So, different social arrangements and relationships can influence the rate at which infants are killed by males, even during periods in which new dominant males attempt to consolidate their reproductive rights.… READ MORE

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