Discriminative Parental Solicitude and the Relevance of Evolutionary Models to the Analysis of Motivational Systems


Discriminative Parental Solicitude

and the Relevance of Evolutionary

Models to the Analysis of Motivational Systems


Claudia Sanchez, Marianela Silva, Chris Murphy, BrianneVanElslander

Loyola Marymount University






Dr. Michael E. Mills

Psych 452








Evolution by Selection and the Proximate-Ultimate Distinction


Evolutionists generally refer to psychophysiology's studies as proximate causal analyses. The behavioral ecology approach concerns adaptive function or ultimate causation. Much has been done to separate these two phenomena but they are ultimately linked. Proximate causal research is guided partly by assumptions about adaptive function. Selectionist theories make these assumptions explicit and help generate testable proximate causal hypotheses. The proximate-ultimate distinction can best be explained through Darwin's theory of "natural selection". Darwin theorized that the adaptive function of all traits is reproductive. Selection favors those traits that enhance survival of the gene and its future offspring. He goes on to say that creatures have evolved to become involved in life-threatening situations for mates, to deplete bodily assets to nourish offspring and in general to expend their lives in the pursuit of genetic fitness. Those who disagreed with Darwin proposed the idea of "greater goodism" which states that selection provides animals with the shared goal of bettering the species. Essentially "greater goodism" only hindered research.

Niko Tinbergen, who shared the Nobel prize in 1937 for his role in establishing ethology as a science, paid close attention to changing ideas about adaptive significance into testable hypotheses. While he knew that proximate cause and adaptive function are distinct, he also recognized that they are complimentary. He pondered why nesting birds would carry the eggshells away after their offspring hatch while presuming that this must serve some adaptive purpose or selection would have eliminated it. His experiments proved that this action made the nest less conspicuous to predators. Further testing of explicit models followed Tinbergen and efforts that were made to separate proximate cause and adaptive function were continually proved pointless. The two are linked, no matter how insignificant the relationship may be.

Organismic goals such as not being hungry and not being frightened further enhance the relationship between the proximate cause and ultimate cause. One may think of feeding as a way to nourish the body, stop hunger pains and maintain survival. This is proximate cause. In order to understand the ultimate cause we look at broody hens. While incubating their eggs these hens are cryptic and experience a decline of 18% in target body weight. This is one example of adaptive anorexias in which the animal's inclination to feed is sensitive to both internal energy reserves and the likely fitness cost of taking time out from other adaptive activities. Similarly the goal of not being frightened holds selectional thinking properties. For example, a male stickleback fish guarding his nest full of eggs will stand his ground longer when a predator approaches then if he had no eggs. He will even dart at the predator and the more eggs he has the more bravely he will protect.

It seems as though any motivational mechanism will be misunderstood until it is examined with regards to the selection theory. This applies to hunger, fear and most of psychology including perception. Organisms have not been designed to simply maintain energy, repair tissues and outlive others but rather selection has designed them to replicate their genes through the somewhat risky endeavors of sexual reproduction and parental investment.




Parental Motivation and discriminative solicitude


Parenting is a very important aspect of the behavioral repertoires of many species, including people. Most women have been known to devote most of their time in nurturing and caring for their offspring. Hence, offspring have become the vehicles of parental fitness. Parental investment can occur in a variety of ways. For example, they can provide food and protection for their offspring. When a parent doubts that the offspring is indeed their own, it reduces the amount of parental fitness payoffs. Among several siblings, parental investment may differ between the younger and smaller offspring in relation to the older siblings. This may occur because of the certainty of parenthood, whether the offspring maintains any reproductive value or simply the fitness value of the available alternatives.


Certainty of Parenthood


The product of the reproductive value of an offspring and its relatedness to the parent determines the offspring's expected contribution to parental fitness. Maternal Motivation demonstrates a mother's investment in her own offspring in relation to non-relatives. Most mothers will discriminate against offspring which is not their own. For example, seals will attack unrelated pups who attempt to suckle. However, experiments have shown that maternal concerns are indiscriminant among laboratory rats. Rats will nurse whatever pup is in their nest, even those of other species. Colonial species are less likely to discriminate against non related species than do dispersed species. Therefore, there is a greater demand for discrimination among colonial species.

Parental solicitude is another matter that exists among species. Males will typically experience parental uncertainty in species where fertilization is internal. This explains why females are more likely to invest a greater amount of time in their offspring as opposed to males. Females who mate with more than one male during a fertile period are entering a "sperm competition." This leads to mate-guarding among the males. This can become extremely problematic in cases where the male invests a great amount of time in their offspring. If mate guarding fails, the male must rely on other cues of paternity such as his share of access to the female when she conceived and similarities or differences in the characteristics of the offspring.

Though there is no evidence of non human males using phenotypes as paternity cues, this technique is prominent in human males. It is common for relatives to find similarities in the paternal kin rather than in the maternal kin. A phenomenon that arises from this belief is the idea that fathers express more affection and investment in their offspring when there is a resemblance.

Another important aspect of parenting is a comparison between adoptive parents versus stepparents. Wilson and Daly present a theory which states that adoptive parents tend to be less problematic than stepparents. One explanation describes adoptive parents as being more readily prepared to accept another's offspring. Adoptive parents have not developed any specific defenses and have evolved a parental psyche. Unlike adoptive parents, stepparents experience adaptive problems because of parental mortality.


Reproductive Value of the Young


Parental investment, such as provision of food, is not an act that is strictly limited to the realm of discriminative parental solicitude. An older offspring -- typically higher in reproductive value, and therefore higher in fitness value to the parent -- subject to less parental investment is not always a less valued offspring. The older offspring may simply be more capable of fending for itself. Greater value for one offspring over another may be revealed when the parent only has an opportunity to save one from death. This situation is difficult to manipulate in nature, but a related method for measuring parental valuation of offspring is often used. This related method observes how much risk the parent is willing to take when defending helpless young from a dangerous predator. Expectedly, an adaptive parental psyche would be willing to accept more risk in defending young with greater reproductive value. Theoretical determinants of reproductive value are brood size and age, as related to reproductive potential.

In humans infanticide is considered to be an adaptive parental defense mechanism. Infanticide occurs when cues of low infant reproductive value are recognized. Examples of these cues are famine during the time of birth or a deformed child. Human infanticide provides a glimpse at the hypothetical question "Which child does one save when the others will perish?" Mothers would usually save the older child, who tends to have greater reproductive value.

Typically reproductive value steadily increases from birth at least until puberty. Thus parental feelings have evolved to value offspring increasingly with age. Parental solicitude does not consistently increase with offspring age however, because the dependence of the offspring dwindles with age.


Alternatives to Present Parental Investment


Alternative uses of parental resources is the last variation of parental response to be considered. Parental efforts are, at times directed toward the offspring that will best promote their fitness. The offspring that are the less profitable option become good elicitors of parental investment. A deeper parental allocation problem is the cost-benefit relationship between parental investment and other fitness promoting activities. For instance, pursuing multiple sexual partners. As parents age, their reproductive value declines, exponentially altering future decision making. Parents continue to accept greater risk as their own reproductive value declines. Measuring reproductive value decline in parents has been far more difficult than the increase with their offspring. The more risk parents accept has many other causes besides a decline in their own reproductive value.

Human females generally show a decrease with age, as their potential reproductive life span ends, in devaluation of young. The variables relevant to changes in maternal solicitude are expected to be similar for fathers. But females' alternative reproductive efforts decline more rapidly than men since their reproductive value declines much earlier than males reproductive value. Dependent children inhibit, although it decreases with age, maternal opportunity costs much more so than paternal opportunity costs. The amount of the differential demands on the mother compared to the father consistently declines after birth. A mother's valuation of offspring relative to the valuation of herself will probably rise more rapidly after birth than the same amount for a father.


Three Stage Theory of Maternal Bonding


It is likely that child-specific parental love involves three processes with different time courses. The stages are: (1) an assessment of the newborn's fitness prospects, based on both the child's quality and the situation; (2) discriminative attachment to the baby as an individual; (3) prolonged and gradual deepening of individualized love.


Initial Cues of Newborn's Fitness Prospects


Assessment occurs immediately after birth. It includes examines the child and how its qualities and current circumstances combine to predicts its prospects. In Western society, during assessment, parents are often shocked and reject children with serious birth defects. This rejection would have led to immediate abandonment in the ancestral settings. In addition, beliefs that deformed babies are ghosts or demons are present sporadically throughout the world. This so-called superstition cannot be dismissed foolish and ignorant, on the contrary it serves as basis of difficult but functional choices.

Maternal responsiveness also varies after giving birth with subtle cues of the infants health and quality. There is an increase risk of abandonment or abuse in small, premature babies. This goes hand in hand with emotional distancing, which has been described among impoverished Brazilian mothers of weak, sickly infants who are likely to die.

Healthy human infants exhibit social responsiveness, within a few hours after birth. This includes eye contact and selective attention to maternal speech. This may be an adaptation for eliciting maternal commitment and eliciting quality during the assessment phase.


Discriminative Bonding to Own Offspring


Parents have a high sensitivity to their babies' distinctive features, recognizing them by voice and by smell. These abilities represent psychological adaptations for discriminative bonding. The new mother not only has to recognize her baby, but also she must develop an individualized commitment to it so that she will be able to invest heavily in its welfare. Many new mother report feeling indifferent to their newborns (perhaps signaling the initial assessment phase, as well as the lack of individuation, but very few feel the same way after a week. After a few days of close contact, mothers report feeling that their babies are uniquely wonderful.


A Gradual Deepening of Parental Love


The third component of parental attachment is much more gradual. The strength of parental love may be expected to grow with the child's increasing reproductive value, especially in the first few years, where there is a steeper increase in that value. This is reflected in the fact that at 16 months after giving birth, mothers talked more and more positively about their babies over time. Importance of the infant was also reflected in that over time, more women felt closer to their babies, were pleased with their infants' development, or enjoying child-care activities.

The information parents gather from their infant's prospects affects the time and depth course of their love and commitment. Since naming bestows personhood and facilitates individuation of affection, in many societies, newborns are not immediately named or acknowledged by the community. This corresponds to a period of high mortality risk, perhaps it occurs in order to make it easier to make difficult decisions of divestment and lessen the emotional pain if the infant dies.




Evolutionary theory is not a substitute for proximate causal analysis, but a valuable aid thereto. Selectional thinking suggests that changes over the reproductive life span may reflect adaptive changes in maternal inclinations as reproductive value and opportunities change. It also provides reason to believe that the focus of cognitive neuroscientists will enlighten family relations better than more sociological approaches.