After reading Diamond

Summary(main idea)
Diamond says that people define 'race' by using visual characters like skin color, eyes and hair. However it is unnecessary because it is not scientific and unclear. it could be possible to divide people into many different sections by using natural selection, sexual selection and no meaning one, but these sections are sometimes overlapped. They are unclear and vague. Thus It is difficult to divide people into biological categories.

Reaction
In class, when Mark gave us some pictures and asked us how many categories would make, I used visual characters to divide them. But after reading this text, I noticed it was not good way because it is unclear. And I was surprised if we use fingerprints to divide people, the result is that most Europeans and black Africans are same! Therefore, visual characters are totally not reliable to divide people.