GRE writing, cortisol production levels and birth order

Material:

The following appeared as part of a letter to the editor of a scientific journal.

"A recent study of eighteen rhesus monkeys provides clues as to the effects of birth order on an individual's levels of stimulation. The study showed that in stimulating situations (such as an encounter with an unfamiliar monkey), firstborn infant monkeys produce up to twice as much of the hormone cortisol, which primes the body for increased activity levels, as do their younger siblings. Firstborn humans also produce relatively high levels of cortisol in stimulating situations (such as the return of a parent after an absence). The study also found that during pregnancy, first-time mother monkeys had higher levels of cortisol than did those who had had several offspring."

Write a response in which you discuss one or more alternative explanations that could rival the proposed explanation and explain how your explanation(s) can plausibly account for the facts presented in the argument.

Alternative Explanations:

Before making alternative explanations for the proposed explanation and how they could account for the facts presented in the argument, I would like to examine the facts. Then I would like to present two explanations from two different perspectives: individual history and  social factors.

First of all, the findings of the study are inconsistent in themselves. The last report that first-time mothers have stronger response to stimuli shows that it is at least the individual history rather than the birth order that affects levels of cortisol produced by each individual. The study describes the subjects as first-time mother monkeys, not first-time and first-born mother monkeys, and this raises the suspicion that the study subjects include individuals of all positions in birth order, and they all secrete high levels of cortisol to stimuli when they have a baby for the first time, while the first two test results show only first-born individuals, both monkeys and humans, secrete twice as much cortisol as younger siblings. This inconsistency allows surmise that experience of doing something first-time counts more than being a first-child in terms of sensitivity to stimulating situations and hence it is very much likely that effects of birth order on an individual’s levels of reaction to stimulation do not exist.

Two alternative explanations could be made for the test results. One is based on the mother’s individual history affecting her first baby's physiological property. Under a plausible condition that the condition of a  mother affects the condition of her baby, the first-born babies share the feelings of their first-time mothers.  Infant-mother relation is so close that they synchronize emotional and physiological changes. Also, it can be easily assumed that a first-time mother is very sensitive to her environment, as doing anything for the first-time makes any individual nervous. Thus the contagion from the first-time mother, who tend to be excitable to even the smallest stimulus and produce a great amount of cortisol, makes her first-born baby react to stimuli in the same way as its mother and produce more cortisol than its younger siblings, whose non-first-time mothers have shared with them more relaxed mother-and-child-hoods.

The other candidate for alternative explanation I could come up with is based on a social factor. A child-birth, especially the first pregnancy and birth-giving of an individual could be a big shift of the individual’s position in the society it belongs to, in both monkeys’ and humans'. Thus, the other individuals around the first-time mother and her first child cannot help having interests in them and attempting to have interaction with the new-arrival. Some adults might come near and examine the baby, while younger individuals may watch in proximity or even incessantly touch the baby from curiosity or animosity. Some aggressive individual may attack the baby. This reaction from the surrounding community may make the first-born nervous about stimulation. The babies that follow arrive after the society has gotten used to the first child, which has established a position in the society, and thus the second or third children may be no more than additions that do not raise any concern in the eye of the members of the society. Humans may also demonstrate not exactly the same but similar reactions to first-born children and the following arrivals. Adults and children react much more strongly to the first baby than to the second or third ones, and the difference of the amounts of cortisol secretion between first-born children and younger children reflects the difference of the magnitude of the influences of these reactions of the society members to children depending on their birth order.

Both of these explanations could account for the facts in the study that higher production of cortisol occurs in such a situation that first-born rhesus monkeys encounter unfamiliar monkeys and first-born humans had higher levels of arousal when their parents were back. Firs-time infants share the fear which their mother monkeys have and are also nervous about encountering other monkeys from bad experiences inflicted by others, so they react strongly to the encounter of unfamiliar monkeys which might attack them, and first-burn human children, who have also become highly sensitive by sharing the anxiety of their mother and by being incessantly meddled with by the members of their society, may react more strongly to separation from and reunion with their parents by dramatically raising the level of cortisol in the blood stream.