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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.
In the argument, the author makes a conclusion that birth order have great influence on an individual’s levels of stimulation. To bolster his argument, the author cite a recent study of eighteen rhesus monkeys, which shows that firstborn infant monkeys produce up to twice as much of the hormone cortisol, as do their younger siblings that in stimulating situations, and during pregnancy, first-time mother monkeys had higher levels of cortisol than did those who had had several offspring. The argument seems somewhat convincing at the first glance, after a careful reflection, however, it is fraught with vague information and unwarranted assumptions.
In the first place, the author assumes without justification that the levels of cortisol can represent the levels of stimulation. However, no sufficient evidence is provided to prove that the level of stimulation is the only factors determining the levels of hormone cortisol. A myriad of other factors might influence the levels of hormone cortisol more greatly, such as the age, the physiological condition and so on. If it is the case, then result of the study is unpersuasive since the hypothesis that the study depends on is wrong. The study shows that firstborn infant monkeys produce more cortisol than their younger siblings in stimulating situations; it is really possible that the dissimilar levels of cortisol might result from the different physiological conditions rather than birth order; the level of cortisol of the monkeys might varied with age.
In the second place, even assuming that the hypothesis that the study relies on is valid, the result of the study is still unconvincing, for the author has been blind to other factors that might lead to high levels of stimulation. The reason, why firstborn humans produce relatively high levels of cortisol when a parent return after an absence, is that firstborn humans have a great affection for their parents while their younger siblings may have never seen their parents at all. Without a thorough investigation about the factors influencing levels of stimulation, the author cannot make the conclusion.
In addition, it is wrong for the author to citing the evidence that first-time mother monkeys had higher levels of cortisol to prove his conclusion, since the comparison has nothing to do with the theme of the study. Unless the author can prove that the mother monkeys, who are firstborn, produce relatively higher levels of cortisol than those who are not, it is might be credible.
To sum up, the argument is of little credibility. To solidify his argument, the author should make a thorough study about the effects of birth order on the levels of stimulation. In addition, the author should also rule out the above-mentioned possibilities.
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发表于 2012-3-19 21:05:19
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