1.  Studies of both animals and humans have shown that sex hormones somehow affect the stress response, causing females under stress to produce more of the trigger chemicals than do males under the same conditions.

等于：than males do under the same conditions.

2.  You spent more money than was intended to be spent.

【答】以上两句中，than 从句表示“比较”意义，than 在从句中作成分：句1，than充当do的宾语；句2，than充当was的主语。

网友可参考：

http://ask.yygrammar.com/q-25371.html