In another twist in the decades-long battle over evolution's status in public school science classrooms, state legislators are arguing that teachers have a right to raise doubts about that essential scientific theory as a matter of free speech. Similarly worded bills that attempt to protect the right of educators and students to present critiques of evolution on the basis of "academic freedom" have emerged in at least five states. Those measures do not call for teaching "intelligent design" or biblically based creationism. Instead, they generally describe evolution as controversial and seek to bar school administrators from interfering with teachers who describe what they see as flaws in the theory. The overwhelming scientific consensus, however, is that there is no debate about the core principles of evolution, which scientists regard as the only credible, and thoroughly tested, scientific explanation for the development of human and other life on Earth, and for its diversity of species. Opponents of the bills see them as repackaged attempts to introduce religious concepts into science lessons by falsely implying evolutionary theory is riddled with doubt.