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 situ

Even at the first glance of the argument to the editor of the scientific journal, some logic gaps are noticeable in connecting the facts presented, which make it flawed.

First of all, a sample of eighteen rhesus monkeys is too small to be used in extrapolating conclusions to the entire monkey species. A proper justification of why eighteen and not any other number of individuals must be provided for it is crucial in order to determine the validity of the study. Was the aggregate population of rhesus monkeys around twenty, then this sample could be representative, but still the results would only attach to rhesus and not necessarily to any other kind of monkeys. Nonetheless, this is not the case because it is for sure there are more than that many rhesus in the world, or they would be considered endangered animals otherwise. So, the results can have mere been by chance in that those who had showed higher levels of the hormone cortisol in front of such stimulations turned to be firstborn due to a deficient selection.

Second of all, the results are not comparable to the humans ones because stimulating situations are clearly different for both groups. An encounter with an unfamiliar monkey differs to the return of a parent after an absence in terms of the sensations caused on the individual, the former induces fear and the later happiness or excitement. Besides, other facets of the firstborn humans under the study must be taken into consideration such as the blood group or their personality. What if most of them have the same type of blood or similar traits in personality? For example, they are of the group 0 which always produces higher levels of cortisol by nature, or they are more homesick than their siblings, which is why reencountering with a long-time-no-see parent excites them more. Then, having high levels of cortisol can be explained by these factors instead of the fact of being firstborn.

And third of all, the finding of first-time mother monkeys having higher cortisol during pregnancy suggests that the level of this hormone is dependent on the phase of life the individual is facing. Obviously, not all first-time mother monkeys are firstborn ones. Therefore, those first-mother monkeys that are not firstborn are going to show a higher level of cortisol than the others that are firstborn monkeys but nor first-time mothers during pregnancy, which contradicts the claim of birth order on the level of hormone.

In summary, there is no consistent clue of the effects of birth order on an individual's levels of stimulation. Many other aspects like the ones exposed above and others need to be scrutinized before arriving a solid conclusion so as to be published in a scientific journal.