they've found other evidence buried deep inside human cells.

　　In a new study，Brendan O'Fallon and Lars Fehren Schmitz report evidence found in genes that the Native American population dropped by half after the arrival of Europeans.O'Fallon studies genes at ARUP Laboratories in Salt Lake City, while Fehren Schmitz is a scientist who studies humankind, at the University of Gottingen in Germany.

　　Cells make up every part of the body.Deep inside almost every cell is a long，coiled molecule (盘绕颗粒) called DNA.Genes are parts of DNA that play important roles in determining one's life.Genes help determine a person's appearance, such as skin color and height, and also play a role in many things you can't see, like the chance of getting a disease.

　　Genes change over time, and by following these changes scientists can learn about a person's ancestors.O'Fallon and Fehren Schmitz looked at genes in the mitochondria of cells.(Mitochondria are like factories that help cells use energy from food.) The scientists compared DNA from the remains of ancient Native Americans with DNA from living people descended (遗传) from Native Americans.

　　The scientists studied patterns in the genes from the two groups and identified ways that the patterns changed over time.Using statistics, which includes useful mathematical tools for analyzing large amounts of data, the researchers were able to judge the size of the Native American population before and after the Europeans' arrival.The comparison showed the number of native people reduced sharply after European settlers landed in the New World.

　　Earlier genetic studies didn't have evidence of the Native American die­off.Scientists involved in the new study say that there's now more data from ancient remains, so researchers can get a better idea of what happened.

　　【语篇解读】　基因承载了人类遗传密码，是随时间的推移而不断变化的。通过对基因的分析和研究，人们可以解开很多秘密。

　　1．When European settlers arrived, they brought to North America.

　　A．smallpox disease B．old documents

C．other evidence D．a new study