"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

While it may be true that in stimulating conditions, firstborn infant monkeys as well as firstborn humans produce high level of cortisol, the argument does not provide enough insight and evidence to corroborate the claim. The argument is rife with holes and unsubstantiated claims that could be countered by alternative explanations.

The writer claims that the study was conducted with eighteen rhesus monkeys, a sample that is not representative. The study ought to have used a larger number of monkeys in the study, because while the eighteen rhesus monkeys may have produced the result, additional monkeys may have proven otherwise.

Additionally, an explanation on the source of the monkeys will help to strengthen or weaken the argument. If the monkeys were selected from the same habitat, then, the argument will be greatly flawed, because, the influence of the habitat on the monkeys may have led to the result, where as if the monkeys where chosen from different habitats all over the world, it would effectively strengthen the argument.

The writer also failed to mention the number of infant firstborn monkeys used in the research. If the entire eighteen monkeys were infant firstborn monkeys, then, it would be difficult to establish how the other monkeys would behave in stimulating conditions. The author should have provided insight on the control groups used in the experiment and how they reacted to the situation.

Finally, the fact the rhesus monkeys reacted in this manner to the study does not necessarily mean that humans will do so. The writer fails to mention whether humans were studied and how they responded to the stimulating conditions to help corroborate his argument.

In conclusion, the writer ought to have provided further explanations on the study, such as the other conditions in place, environmental factors and how these monkeys reacted to the entire setup and to the handlers as well. Any of these could have accounted for the high level of cortisol produced in the stimulating conditions.