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.
C1: A recent study of eighteen rhesus monkeys provides clues as to the effects of birth order on an individual's levels of stimulation.
G1: 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.
G2: Firstborn humans also produce relatively high levels of cortisol in stimulating situations (such as the return of a parent after an absence).
G3: The study also found that during pregnancy, first-time mother monkeys had higher levels of cortisol than did those who had had several offspring.
P1
In this letter to the editor, the author claims that birth order has direct effects on the stimulation levels of infants and pregnant mothers as manifested in the levels of cortisol. While being firstborn is correlated with high stimulation levels, there are a number of alternative explanations we need to take into account when evaluating the soundness of the argument.
P2
First of all, we may explain the high stimulation levels of firstborn infants in terms of their relatively older ages. In both studies of monkeys and human infants, firstborn infants have to be compared with their younger siblings when being exposed to certain stimulating situations. Maybe the firstborn babies responded to the stimulation more actively simply because they were older and with better cognitive abilities they were more sensitive to potential danger of an unfamiliar monkey or the excitement of a returning parent. The higher level of cortisol could be the result of the intense emotional changes rather than being firstborn.
P3
Related to age is the relatively larger body sizes of the firstborn babies which may lead to higher levels of cortisol being released. Assuming the amount of cortisol produced is proportional to the body size, the larger the babies are the more cortisol would be produced given the same level of stimulation. Therefore, we need to control the body size if we want to better understand the effects of birth order on stimulation level.
P4
Although the siblings usually share similar genes, firstborn babies are not genetically identical to their younger brothers or sisters. Therefore, the different levels of stimulation could result from the different genes of the infants. Since the sample size was relatively small, it is possible that infants that are genetically geared towards releasing more cortisol happen to be firstborn. Studies of larger random samples are necessary to tease out the effects of genes from the effects of birth order.
P5
As for the first-time expecting mothers, birth order may not be the direct cause of high level of stimulation. Maybe the first-time mothers were more excited or nervous about being pregnant which lead to higher level of cortisol being released. Or the pregnant mothers with children were too busy taking care of their children to feel excited or nervous. Therefore the level of excitement or stress could be a better explanation for the level of stimulation.
P6
In conclusion, a number of alternative explanations may be advanced for the high level of stimulation observed. Unless we could find concrete evidence to rule out such explanations, the argument is not very strong.
个人感觉P2的论证不太好，年龄大-对危险认知更强-情绪波动变化更大导致激素增强，觉得这里的路太长了，将年龄大对危险认知更强放在一起写会更好，老师觉得改成这样如何：
First of all, we may explain the high stimulation levels of firstborn infants because of their better recognitive abilities in a relatively older ages.
如果要解释是因为“年龄原因”，您觉得这么写如何？
First of all, we may explain the high stimulation levels of firstborn infants in terms of their relatively old ages. In the study of first born infant monkey, they produce much more hormone cortisol, when encountering with unfamiliar monkey. But actually, it is possible that when the second born monkey has grown up in the same age, they will produce the hormone cortisol at the same level. Such phenomenon suggests, it is individual maturity or other phyisical factors during the growth that enhance the increase of hormone cortisol, not due to the monkey's birth in a certain order.作者: 麦小粥 时间: 2018-5-25 04:32:59