"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

The argument that birth order has an evident effect on one’s stimulation levels, supported by a lately research on rhesus monkeys as well as two other evidence, may seem logical and somewhat appealing at first glance. However, a close examination reveals that the conclusion is oversimplified and problematic. The proposal can be easily countered by the following alternative explanations.

First and foremost, is birth order the only factor or, even is it one factor that accounts for the variation of hormone levels in rhesus monkeys? Hormone secretion may be inherently different in different age groups of monkeys. For example, the eldest monkey may be much older than its siblings and thus should have naturally higher levels of cortisol than the younger ones. And the reliability of the study is questionable. The scale of eighteen monkeys may be too small to represent the general situation. Or the sample may not be randomly selected and it is possible that only these monkeys under research appear to have difference in cortisol levels, while the majority does not. And also, the author does not provide details of the experimental methods. Lacking in evidence of control group, it may be quite possible that other factors instead of birth order that contribute to the hormone level variations.

Second, the fact that first-born human beings secrete high levels of cortisol under stimulations lacks control group to compare with. The average levels of cortisol in every individual may be high, not only in first-born people. The hormone levels in younger siblings may well be as high as in the oldest ones that there may not be significant difference. Other factors such as disease or aging, rather than birth order, may cause the increasing of hormone. Thus, without clear evidence to support the author’s claim, we cannot hastily to make a conclusion.

Third, the phenomenon that first-time pregnant monkeys have higher cortisol levels than other pregnant ones has no direct cause and effect relationship with the author’s argument. In general, pregnance will engender a series of hormone change in body and there is great variance among individuals. In addition, the hormone variation in mothers does not lead to the difference in their offspring. Furthermore, the case study does not measure the overall situation in all living things.

To sum up, the author comes to a conclusion too hastily and the validity is questionable. There are many other plausible answers to the stated phenomenon. If the author provides more details about the research and prove the reliability of the study, the conclusion can be more convincing.