The purpose of poll taxes in southern states was to

... discourage African Americans from voting.

Poll taxes means you have to pay a tax before allowed to vote.  That's a way of preventing poor persons (like blacks in the South) from voting.

In addition to poll taxes, other measures were also used to block blacks from participating in the voting process. For instance, literacy tests would require persons to pass certain standards of reading and writing in order to qualify for voting.  These tests were aimed at blacks, who had not had access to the same education as whites.

- "the past is made of multitudinous items ranging from anything that can be collected, recollected or assessed to originate in the past. as such, the past is a gallimaufry of particulars that may not have been related in any way. however, the human mind seeks organization to understand concepts and other things. the human mind therefore seeks relationships in explaining and studying the past. history being a humanity, dictates that historians have to serve this human trait by bringing structure to details of the past. historians do this by creating interpretive frameworks that capture as many details as possible."

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genetics is the study of how dna works, the methodologies defining the new recent technologies allow scientist to have a panoramic view of the entire dna landscape, especially how genomes interact with their environment, including off course, factors outside their organisms.

thus is very possible the existence of both scenarios, where populations of isolated individuals have different genetic traits, and share traits related to genetic mutation, due rats can easily travel overseas using human transport channels. so scientists could get a vast number of data, including human interaction, evolution of rodents, health development, spread of infections, development of new organisms, how genomes evolve in different environments and so on.