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.
While the reasoning of this letter may seem correct at first glance, there are some unwarranted assumptions that should be considered and there are lacks of proper correlation between the two main facts. The individual's level of stimulation can be a result of not only a birth order, but also other factors. The author of the letter concentrated only on a birth order and did not take into consideration other possibilities of these effects. Furthermore, what has been concluded for monkeys’ does not demonstrates that humans must possess the same characteristics.
Firstly, the wording of this letter should be taken into account. We cannot find an exact information when the study was carried out and the term 'recent' is rather vague and maybe the research is already obsolete. The author did not inform readers about the selection process of the monkeys. The chances are that this type of effect is common only for this specific group of monkeys and can be a result of an environment in which these very rhesus monkeys were nurtured. The question should be asked how the researchers made sure that the unfamiliar monkey was not met beforehand. Another question worth asking is how the stimulating situations were chosen. The conclusion was based on a sample size of eighteen monkeys. This was not justified why this number of monkeys was sufficient. A sample size is generally a large number and should contain a wide variety of individuals. Moreover, it wan not specified how many of the eighteen monkeys were parents, first born or younger siblings.
Secondly, we can argue that there are other reasons of the increased level of the hormone cortisol. Generally, probably this consequence can appear whenever there is a stimulating situations, especially the one that has to be handled for the first time. It could have happened that during the experiment the oldest sibling was always of a different sex than the unfamiliar monkey. It could have altered the first-born monkey reaction and, for instance, if it had been a male monkey it could have reacted more passionately for the unknown female monkey than its younger sister. We can call this a sex-oriented result.
Thirdly, we do not know all the simulating situations that were checked in case of firt-born humans. The example given with a parent coming back after a long absence can also analysed in terms of sex differences. For example, a reaction of an older daughter can be passionate, whereas a reaction of her younger brother can be even apathetic. The upbringing of children can also be influential for such feedbacks. Perhaps, a mother could have read slushy stories to her first-born, while a father could have read stories about valiant and almost unemotional knights to his younger children. This kind of conditioning could have influenced the following children's reactions to simulating situations.
The last issue to be considered pertains to first-time mothers. The higher level of cortisol could have been caused by conditions in which the monkey was kept or the type of food which was given to her. Maybe, the mother with several offspring were kept in much better or worse conditions. At the same time, an elder mother with several children could have produced more cortisol as a result of her awareness of being too old to be able to deliver health children.
Hence, the birth order may be relevant to some extent in the stimulation level of individuals. However, there may be certain other factors that are more relevant than the birth order such as those discussed above. Further studies and a larger population data maybe more convincing for that matter. The study was concentrated only on one type of causation and there are a few fallacies and inaccuracies in the argument. The author should have provided us with more information about the research process and give more cogent arguments for his or her theory.