The widespread use of Roundup, a common herbicide developed by Monsanto, has caused weeds that are resistant to the chemical to spring up on a half-million acres of agricultural land across the U.S. At fault, scientists say, is the popularity of bioengineered crops that are “Roundup Ready” — that is, created by Monsanto to be genetically impervious to the herbicide. Together, Roundup and Roundup Ready crops make life simpler for conventional farmers, who can use just one herbicide and spray it directly on their crops. The ease of the practice has led to widespread use of Roundup, and that has led to evolution taking its inevitable course: Those weeds that can survive exposure to Roundup are flourishing. Further spread of resistant weeds could wreak havoc around the globe, because glyphosate — the generic name for Roundup — is the most popular weed-killer on the planet. So far, the U.S. government has not imposed any limitations on the use of Roundup or Roundup Ready crops.