How thin people have been since ancient times.

Since ancient times, people's hearts have been thin and cold, and the next sentence is why kindness is not always. A complete sentence is how thin and cold people have been since ancient times, and why kindness is not always there. The first half of the sentence means that there are not many people who are really affectionate and righteous from ancient times to the present, and the second half expresses that kind people often don't stick to the end.

Society is the sum total of the relationship between biology and environment.

Human production, consumption, entertainment, politics and education all belong to the category of social activities. The social behavior of animal or other creatures also belong to that social category.

Society refers to an unchangeable structure that creatures living together in a specific environment can maintain for a long time and cannot leave each other (society is also distorted as an adjective to describe people living in crowds, especially gangsters, which are widely used among young people).