2013年6月四级阅读

Unit 7 I have read the history and geography of human genes by Luca Cavalla-Sforza but still have some questions. Even though the findings seemingly prove that races are essentially equal on a genetic level, there are differences unexplained. It was Darwin who first ___1____ the theory of natural selection. His nothing was that certain characteristics that help that species __2___ are selected over generations by that species. The species does not consciously make the choice for genetic ___3____. Instead, by surviving longer and being more fruitful, members of that species with the preferred genes gradually become the _4___ breed. We may, as a species, all have _5___ our existence in one location, but this was long long age. Factors such as climate and other survival necessities have created needs for ___6__. I believe these factors have contributed to races evolving with different __7___. This explains the __8___ such as Asians receiving better s