The following appeared as a 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 si

The author proposes an abstruse explanation of the nexus between firstborns of humans and monkeys. According to the argument the result of the study shows that the stimulating situations affect only the first timers – firstborns and first-time mothers- which catalyse the increase in the level of cortisol. But, there is no plausible explanation presented as to why this happens.

One can argue that the description of the high levels of cortisol in firstborns may be credible, but presenting similarities between a human and a monkey based on one fact is unacceptable. The cortisol level in monkeys seems to rise during an encounter with an unfamiliar monkey whereas for its human counterpart it occurs on the return of a parent after an absence. These two situations show certain anomalies. A parent, whom the child may not have seen for a long time, is not exactly a stranger. As there is no analysis provided for the reason for the rise in levels of cortisol, one possible explanation for this can be said that in humans the absence of a parent for a prolonged period of time may lead to the child craving for the love and affection of that person leading to the high levels. For the rhesus monkey, the situation is completely different. Fear and/or curiosity in meeting an unfamiliar monkey may also lead to the increased level of cortisol.

Juxtaposing the argument of the levels being higher for the firstborns than their younger siblings in humans and monkeys, one can point out the lack of evidence that proves the two being at par with each other. In case of the humans it may be that the younger siblings are under constant protection and surveillance of the older ones. They do not, therefore, feel the wanting of an adult for love and affection. There is a lack of evidence that says that if the younger siblings were left alone the cortisol levels would remain the same. Maybe they would change. Now, in case of the rhesus monkey, while meeting a complete stranger the younger siblings might be with their older ones. This suggests the presence of a generic feeling of protection in the younger ones; their older sibling is there to protect them from the stranger monkey. Again, there is no evidence provided which suggests that the younger siblings were alone while meeting the stranger monkey.

It so happens that for a certain group of rhesus monkeys the level of cortisol is high. Hence survey of the behaviour in just 18 monkeys is not enough to determine whether the similar thing occurs in all rhesus monkeys. There is no proof that the monkey selected belonged to different groups. Moreover, it is not mentioned as to how many humans were observed to come up with such conclusions. Unless a discreet palpable observation is done the conclusion might not hold true.

While it may be true that the first time mothers have higher levels of cortisol than the monkeys with several babies, it cannot be inferred that the similar thing happens for the humans. There is no statement which proves otherwise.

The rhesus monkeys may be similar to humans in their own way but the similarity indicated in this argument may not be one of them. There is ample lack of evidence that shows similar reasoning.