英语语法问题Human beings in all times and places think about their

英语语法问题
Human beings in all times and places think about their world and wonder at their place in it. Humans are thoughtful and creative, possessed of insatiable curiosity. 61) Furthermore, humans have the ability to modify the environment in which they live, thus subjecting all other life forms to their own peculiar ideas and fancies.
请问最后一句，thus 后面的subject为什么用ing形式。