The defection hypothesis--论文代写范文精选

贝克的研究指出，母亲会憎恨他们的大孩子,把它们推开。因为年长的孩子会影响对新生儿的投资成本,母亲可能会选择集中精力对待婴儿，如果丈夫为了孩子会关注新生儿，母亲可能不会这样。下面的essay代写范文进行详述。

Abstract 
This essay presents a functional hypothesis for the second major symptom of PPD: loss of interest. If a mother’s sad or depressed mood informs her that she has suffered a reproductive cost, then it is possible that she will act to reduce this cost in order to allocate her finite resources to more beneficial ventures, consistent with PI theory. We should therefore expect mothers with PPD to frequently experience a loss of interest in the infant, and, indeed, this is a prominent symptom of PPD (APA, 1994; Beck, 1992; Beck, 1996b; Campbell et al., 1992). Not only do mothers with PPD often lose interest in their child, they frequently have thoughts of harming them (Jennings et al., in press). Loss of interest in the infant is not the only strategy mothers have to reduce their costs, however. Conceivably, they may decide to direct a greater proportion of their time and energy towards their infant by losing interest in other activities like caring for older children, caring for other family members, doing household chores, working, etc.

Beck notes that mothers in her study were unable to cope with more than one child at a time, resented their older children, and pushed them away. Because older children are more likely to survive with reduced maternal investment than are newborns, mothers with a viable offspring or an offspring with reversible health problems, may opt to focus their efforts on the baby if they can count on the husband or relatives taking care of the other children. Similarly, mothers may have to reduce their investment in their husbands in order to focus all their effort on the newborn. 

Thus, when mothers have a healthy baby and a supportive mate, but also have significant and time consuming responsibilities like caring for other young children, family members, their mate, or producing income, etc., they may defect from these other responsibilities in order to invest in the newborn. Excessive non-infant related responsibilities may also predict PPD, with loss of interest applying to activities other than infant care. While PPD may be an adaptation to defect from any costly activity during the puerperium, a focus on loss of interest in the infant is warranted since this symptom is likely to have the greatest detrimental effect on child development, a serious negative consequence of PPD (e.g., Murray, 1992; Whiffen & Gotlib, 1989). 

Many women with PPD are unable to feel any joy or love in taking care of their infants, and often have obsessional thoughts about harming them (APA, 1994; Beck, 1992; Beck, 1996b; Jennings et al., in press), symptoms which are clearly consistent with a desire to defect. Similarly, “negative emotions while with the baby” are significantly correlated with PPD If PPD is, in part, an adaptation to motivate women to reduce investment in their offspring under certain conditions, then women who did not want to be pregnant in the first place should be at higher risk for PPD. 

This is in fact the case. Field et al. (1985) found that an affirmative prepartum response to questions like “was your pregnancy unplanned?,” “do you regret being pregnant?,” “can you say that you do not desire to have a child?” (in addition to other questions—see figure 2) significantly distinguished women with PPD from those without. Similarly, Campbell et al. (1992) found that not being happy about the pregnancy distinguished women with PPD from those without. 

Finally, Kumar and Robson (1984) found that women with PPD had significantly more often considered an abortion. While PPD is defined primarily by affective and cognitive symptoms, if it is an adaptation to reduce investment in offspring, then it must have, on average, actually have modified ancestral mothers’ behavior in a way that prevented them from attaching to or investing in their infants. Beck’s meta-analysis (1995) of 19 studies on the effects of PPD on mother-infant interactions (total number of dyads = 829) indicates that PPD has a moderate to large negative effect on maternal-infant interaction. 

In these studies, observers who are blind to the mothers’ depression status rate her interaction with her infant. Mothers with PPD are observed to have significantly increased disengagement, negative affect, flatness of affect, irritation, tenseness, annoyance, and intrusiveness towards the infant on the one hand, and significantly less warmth, delight, positive regard, sensitivity, activity, contented facial expressions, imitative behaviors, contingent responses, and game-playing on the other. 

In addition to exhibiting more negative emotions and fewer positive emotions towards their infants, mothers with PPD are less responsive and less sensitive to infant cues, have a less successful maternal role attainment, and have infants that are less securely attached (Beck, 1995; Beck, 1996b; Cohn et al., 1990; Cohn et al., 1991; Field & et al., 1985; Fowles, 1996; Hoffman & Drotar, 1991; Murray, 1991; Murray & Cooper, 1996). By being less responsive and less sensitive to infant cues, mothers with PPD are clearly mothering less. The above studies indicate that mothers with PPD are ambivalent about their pregnancies, have difficulty emotionally investing in, and interacting with, their infants, and are less sensitive and responsive to their infants. These manifestations of PPD strongly support the “loss of interest” and “reduced investment” in the infant predicted by the defection hypothesis. 

Whereas loss of interest in the infant has a straightforward interpretation in the context of PI theory, loss of interest in virtually all important life activities presents a more difficult though perhaps more important theoretical problem, and possible adaptive functions for this symptom vis-à-vis evolutionarily significant risks and dangers of the puerperium will be offered in the next section. These more speculative functions generalize the hypothesis to renegotiation or defection from relations with the father and family members in an attempt to solve two problems: increase the levels of investment of others, or reduce the social costs of defecting from childrearing.

Negotiation
Why, if caring for a newborn or engaging in other activities is not in a mother’s reproductive interest, does she not simply stop engaging in the offending task? Why does she experience the distress of depression with its numerous attendant symptoms? Since a significant fraction of depressions postpartum are minor (Whiffen, 1992), most mothers with PPD may in fact only experience a few symptoms consistent with “low mood.” The psychological pain hypothesis well accounts for these cases. A significant fraction of cases of PPD are major depressions, however. For example, in their study of 1033 new mothers, Campbell and Cohn, 1991 found that among women with clinically diagnosed depression, 38% had major depression, 31% had probable major depression, and 31% had minor depression.

So far, this paper has presented a functional argument for symptom one, and a partial argument for symptom two—a loss of interest in particular, as opposed to virtually all, activities. These two symptoms would have delivered benefits to ancestral mothers with a low viability infant or who lacked sufficient social support; when they appear in isolation, or with only one or two other symptoms, they are consistent with a minor depression. The data strongly support the view that minor postpartum depression is an adaptation. If these other symptoms of major depression are adaptations, then they must have delivered benefits to ancestral mothers, yet they seem designed to prevent the acquisition of benefits. 

A marked loss of interest in virtually all activities, significant weight loss, hypersomnia, psychomotor retardation, fatigue or loss of energy, and a diminished ability to think or concentrate would all have impeded ancestral mothers from engaging in critical, beneficial activities unrelated to childrearing, such as food gathering and consumption, buffering food shortages, personal hygiene, avoiding environmental hazards, information gathering, helping relatives and friends, etc. The costs of these symptoms could easily have outweighed the benefits of the first two symptoms, seriously undermining the argument that major PPD may be an adaptation. The hypothesis I will explore here is that major depression prevents individuals from acquiring benefits by design. The extraordinarily distressing symptoms of major depression, almost universally interpreted as pathological, may in fact be functional.

Psychological pain theorists have suggested that individuals who have recently suffered a “social injury” should devote time to evaluating the causes of this injury before embarking on new social ventures (Alexander, 1986; Nesse, 1991; Nesse & Williams, 1995; Thornhill & Thornhill, 1990; Thornhill & Thornhill, 1989; Tooby & Cosmides, 1990). They argue that ‘lack of interest’ may function to prevent an individual from engaging in new social ventures before fully evaluating the failure of the previous social venture. However, I do not find this argument persuasive in accounting for the symptomology of major depression (a syndrome that most evolutionary researchers on depression do not view as an adaptation in any case, e.g., XX). 

First of all, a diminished ability to think or concentrate and hypersomnia are precisely the opposite of what one would expect if individuals were attempting to evaluate a recent social failure—individuals should devote considerable thought to, and concentrate on, the failure, not be prevented from doing so by depression. Second, while individuals would be expected to devote additional time to evaluating a recent social failure at the expense of pursuing new social ventures, they would not be expected to put their physical health at risk. 

Psychomotor retardation, a marked loss of interest in virtually all activities, fatigue and loss of energy, weight loss, and hypersomnia would have endangered the lives of individuals living in small, hunter-gatherer groups by impeding their efforts to feed, care for, and protect themselves. Indeed, it is difficult to see how a symptom like significant weight loss can have any utility vis- à-vis evaluating a social failure. Adaptations evolved because they solved recurring reproductive problems in ancestral environments. In particular, psychological adaptations evolved to extract information from the environment that was relevant to reproductive problems, and to then generate behaviors, that, on average, solved these problems. 

Mothers with insufficient social support and/or a costly infant faced two major problems: how to negotiate increased investment from others, or, how to avoid the severe social costs they may have faced if they neglected or killed their offspring. Just as mothers are unlikely to automatically invest in every newborn, fathers and family members are unlikely to automatically invest either. New mothers wishing to raise their infant may then face the problem of negotiating levels of investment from each of these interested parties. If other members of the mother’s social environment have the potential to invest more, the mother may be able to elicit more investment than she is currently receiving, making the childrearing venture profitable. She should not immediately abandon the child without first seeing if she can negotiate greater levels of investment. I argue that major PPD may be a strategy to negotiate greater investment from the father and kin, or to reduce the mother’s costs, by functioning somewhat like a labor strike (see Watson & Andrews, unpublished ms, for a similar view). 

In a labor strike, workers withhold their own labor in order to force management to either increase their wages and benefits, or reduce their workload. Similarly, mothers with PPD may be withholding their investment in the new and existing offspring, or, in cases of very severe depression, putting at risk their ability to invest in future offspring by not taking care of themselves. This may force the father and kin to increase their investment and/or allow the mothers to reduce their levels of investment. 

Trivers’ theory of reciprocal altruism (1971), and later work on the evolution of cooperation that it inspired (see Axelrod and Dion 1988 for a review), help provide a more general formulation of the “labor strike” analogy. Like the relationship between a worker and her boss, the human pair bond is a cooperative venture—both the mother and father agree to participate in the mutually fitness enhancing endeavor of child rearing. As models of the evolution of cooperation make clear, individuals will evolve to provide benefits to others only if they are free to defect from these activities (e.g., quit) should their costs outweigh their benefits. If the costs of child rearing outweigh the benefits, mothers (and fathers) will need to defect from this costly endeavor—they will need to stop investing in the offspring. The ability to defect from costly endeavors is a key component of any cooperative enterprise. Non-kinship based reciprocity cannot evolve or be maintained in the population if individuals do not have the ability to defect (e.g., Axelrod & Dion, 1988; Axelrod & Hamilton, 1984), a result with the disturbing implication that child neglect and abandonment are necessary for the evolution and maintenance of cooperative childrearing.

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