Animal DNA in PCR reagents plagues ancient DNA research

Molecular archaeology brings the tools of molecular biology to bear on fundamental questions in archaeology, anthropology, evolution, and ecology. Ancient DNA research is becoming widespread as evolutionary biologists and archaeologists discover the power of the polymerase chain reaction (PCR) to amplify DNA from ancient plant and animal remains. However, the extraordinary susceptibility of PCR to contamination by extraneous DNA is not widely appreciated. We report the independent observation of DNA from domestic animals in PCR reagents and ancient samples in four separate laboratories. Since PCR conditions used in ancient DNA analyses are extremely sensitive, very low concentrations of contaminating DNA can cause false positives. Previously unidentified animal DNA in reagents can confound ancient DNA research on certain domestic animals, especially cows, pigs, and chickens.     

Clinton,Congress, and Cuba Policy Between Two Codifications: The Changing Executive-Legislative Relationship in Foreign Policy Making

We examine the changing dynamics of institutional control over U.S. policy toward Cuba that have played out during the time between two codifications of Cuba policy: The 1996 Helms-Burton legislation that codified the long-standing embargo policy as law, and the 2000 bill that wrote travel restrictions into law. The study of who makes U.S. foreign policy has long been characterized by a debate over the respective roles of the president and Congress in this area, but-in theory, at least-Helms-Burton should have put an end to the scholarly debate about who makes Cuba policy: With codification, Congress does. But the practice of making Cuba policy has been more complicated than it might have first appeared in March 1996. We track the politics of Cuba policy between these two codifications and try to understand what they mean for who makes Cuba policy now, and speculate about what these dynamics may more generally mean.