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 situat

The excerpt from a letter to the editor of a scientific journal suggests a correlation of birth order among rhesus monkeys and individual levels of hormonal stimulation. The letter further extrapolates this deduction and applies to human behaviour as well. Even though the case presented is intriguing and the correlation between primates and human beings has always been a fascinating study, the links presented seem weak and could have alternate explanations.
The study defines encounters with unfamiliar monkeys to be stimulating conditions, but there could be other factors that can stimulate hormonal secretions in an individual. Hormonal behaviour is unique per individual given a small sample space of eighteen monkeys; what may appear to be high or low could be in the same range when normalized among a larger set of monkeys. Thus what appears to be a stark comparison between siblings in their infancy, it may not be significant. Especially if the quantities mentioned are very small, “double the quantity” may not be enough as a data point.
Furthermore, an infant’s hormonal characteristics could also have a correlation with the mother’s hormonal status, diet as well as environment during the pregnancy. It is possible that the conditions of birth were not identical, and these differences impacted the hormonal behaviour of the infants. Thus it need not be the birth order but the status of the pregnant mother that could be the causal factor.
Interestingly in line with this theory, the final statement brings up the cortisol levels for the mother monkeys in their different pregnancies. It has been presumed that the cortisol levels were high during the first pregnancy specifically because it was their first pregnancy. But there could be environmental stress conditions during that period – for example high temperature, drought, or stress because proximity of a predator. As cortisol primes the body for increased activity levels, these external factors should be analysed. These factors, if different from the subsequent pregnancies, could also explain the difference in the levels.
Finally, the author inserts a correlation of firstborn humans producing high level of cortisol in stimulating situations. The argument doesn’t specify if a study has compared these levels across siblings of the same family, or firstborn and younger children of the same age from different families. The amount of hormones secreted could be linked to age, which would explain why firstborn would secrete more as compared to their younger siblings. Again the hormonal characteristics could be directly correlated to genetics and family background and thus studied appropriately.
The presented case could have had the potential to be a very illuminating study, possibly highlighting the protective behaviour of older siblings. However the arguments are not directly convincing as they could have alternative explanations, such as those mentioned above, that rival and de-stage the proposed correlation.