1.
One difficulty is that almost all of what is called behavioral science continues to trace behavior to states of mind, feelings, traits of character, human nature, and so on.
句子分析：
第一、句子可以拆分为两段：One difficulty is that almost all of what is called behavioral science / continues to trace behavior to states of mind, feelings, traits of character, human nature, and so on.
第二、句子的结构是：
1)主干结构是表语从句One difficulty is that...
2)almost all of what is called behavioral science是表语从句中的主语部分，后面是简单的谓语和宾语结构。第三、词的处理：continues to trace behavior to继续针对……研究行为
behavioral science 行为科学
states of mind 心态，意识状态
feelings 感情
traits of character 性格特点
2.
The behavioral sciences have been slow to change partly because the explanatory items often seem to be directly observed and partly because other kinds of explanations have been hard to find.
句子分析：
第一、句子可以拆分为三段：The behavioral sciences have been slow to change/partly because the explanatory items often seem to be directly observed and/partly because other kinds of explanations have been hard to find.
第二、句子的主干结构是：主句+两个并列关系的原因状语从句之所以……，部分是因为……，部分是因为……
第三、词的处理：
the explanatory items 用以解释的要素(内容，项目)
other kinds of explanations 其他解释方式
3.
The role of natural selection in evolution was formulated only a little more than a hundred years ago, and the selective role of the environment in shaping and maintaining the behavior of the individual is only beginning to be recognized and studied.
句子分析：
第一、句子可以拆分为四段：The role of natural selection in evolution/was formulated only a little more than a hundred years ago, /and the selective role of the environment in shaping and maintaining the behavior of the individual/is only beginning to be recognized and studied.
第二、句子的主干结构是两个表示时间对比的并列句The role of...was formulated only..., and the selective role of...is only beginning to...每一个句子的主语都比较长，都是名词+介词短语结构。
第三、词的处理：
in evolution 在演化中
formulated 阐述；表述；解释；论证
shaping 形成(造就)
maintaining 保持，维护
recognized 认可，承认
