新argument 2求讨论分析~~

crystallu929UID：3003756

新argument 2 关于birth order的那个题目是道新题，我想了好久只想出一两条理由驳斥，还比较牵强。。。求帮助啊。。。

"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 produce up to twice as much of the hormone cortisol, which primes the body for increased activity levels, as do their younger siblings. Firstborn humans also produce relatively high levels of cortisol in stimulating situations (such as the return of a parent after an absence). The study also found that during pregnancy, first-time mother monkeys had higher levels of cortisol than did those who had had several offspring."

Write a response in which you discuss one or more alternative explanations that could rival the proposed explanation and explain how your explanation(s) can plausibly account for the facts presented in the argument.

我想到以下两个alternative explanations:
1.这有可能不是先天的birth order决定的，其他因素也有影响，比如家中第一个出生的会成熟的较早，责任较多，对弟弟妹妹有保护意识，长久而来应激能力也就比较强，不能单纯下结论说是先天决定
2.选取的样本容量只有18个，不具有代表性，样本是否全面也影响了这个试验结果
3.first-time mother也可能是自己的一种应激性的表现，会产生更多的cortisol，而且这也不意味着这具有遗传性，她们第一胎产下的孩子不一定也就像妈妈一样能够产生更多的cortisol

请问还能想到其他的么。。。我觉得我想的都比较牵强啊。。。求高人指点