Biological characteristics to people into consistent race

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Could you please answer the follwoing question according to terms and contents in Sociology? (not biology or psychology)

1. Why is it impossible to use biological characteristics to sort people into consistent races? 

Here are some texts you can consider

Classifying humans into groups is a subjective process, influenced by cultural ideals and political priorities. For example, Brazil has more racial categories than the US. In Haiti, one is considered 'white' if you have any amount of European ancestry. Thus if you change criteria, people fall into different groups. You cannot draw any conclusions about those groups beyond what you used to sort people in the first place. Biologically speaking, traits are inherited non-concordantly, which means they are inherited independently, rather than packaged together. If you know one thing about someone, it does not necessarily tell you anything else about them, so it doesn't make sense to talk about group race characteristics. In addition, since there is not one gene or trait that distinguishes all members of one so-called race from all members of another, there will be overlap in any racial classification scheme.

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