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 author has tried to make very generalized claims based on the study of 18 rhesus monkeys. He has very conveniently made assumptions about monkeys as well as human beings based on a sample of 18 rhesus monkeys. There are certainly many flaws in the above article which is highlighted by the sample size, the population concerened which I will discuss in the following paragraphs.

First of all he has used a sample size of only 18 rhesus monkeys. Such a small sample cannot be a representative sample set for all the rhesus monkeys. It is not necessary that if 18 monkeys showed increased levels of cortisol all of them will do that.The sample does not clearly reveal as to there were how many first order infants and there were how many non first order infants. There could be a possibility that both of them were not equally distributed. May be the first order infant population was higher or vice versa.

Also we do not have evidence to show that cortisol was elevated because of unfamiliar stimulus. It could be elevated due to some other reason also that is due to the increase in some other hormone like adrenaline which prepares the body for flight fright or fight. It could also be elevated due to hunger. Mother of first order infants are less experienced in handling kids and understanding their cycles than mothers of consecutive offsprings. So there is no real evidence to prove that increase in activity was due to increase in cortisol levels.

There is also no mention of the levels of cortisol in unfamiliar situations. There might be a posssibility that cortisol levels remain high throughout the infancy as opposed to when they are exposed to unfamiliar situations. The study has only compared first order and non first order monkeys in unfamiliar situations. But there is no evidence to show the levels of cortisol in the first order monkeys in familiar an unfamiliar situations.

The author has generalized his conclusion of rhesus monkeys to human beings. If at all he has studied about them he has not mentioned the sample size, the procedure he used to carry out this study and the age of the infants he used in his population to carry out the study.

Lastly the author has also not given a clear idea of the number of first time mothers and the number of mothers of several offsprings were tested. Also there is no mention of under which situations did they have an increased levels of cortisol.

I would say that it is a very vague compilation of ideas stated by the author. The sample size of the rhesus monkeys should have been larger and a clear division of first order infants and non first order infants should have been made. He should have also tested first order monkeys under familiar situations for their cortisol levels. This would have confirmed his allegation that they do no not have increased cortisol levels throughout and it only increased when they were placed under unfamiliar situations. Also evidence of the study done on humans shpould have been given. The precise number of first time mother monkeys and mothers of several offspring should have been stated. All these points would have made the article more stronger.