relies on observation and logical inference. In such fields, the test of falsifiability is satisfied when a theory is used to predict the results of new observations. When such observations contradict a theory's predictions, it may be revised or discarded if an alternative better explains the observed facts. For example, Newton's theory of gravitation was replaced by Albert Einstein's theory of general relativity when the latter was observed to more precisely predict the orbit of Mercury. Unreliable evidence A related objection is that evolution is based on unreliable evidence, claiming that evolution is not even well-evidenced. Typically, this is either based on the argument that evolution's evidence is full of frauds and hoaxes, that current evidence for evolution is likely to be overturned as some past evidence has been, or that certain types of evidence are inconsistent and dubious. Arguments against evolution's reliability are thus often based on analyzing the history of evolutionary thought or the history of science in general. Creationists point out that in the past, major scientific revolutions have overturned theories that were at the time considered near-certain. They thus claim that current evolutionary theory is likely to undergo such a revolution in the future, on the basis that it is a "theory in crisis" for one reason or another. Critics of evolution commonly appeal to past scientific hoaxes such as the Piltdown Man forgery. It is argued that because scientists have been mistaken and deceived in the past about evidence for various aspects of evolution, the current evidence for evolution is likely to also be based on fraud and error. Much of the evidence for evolution has been accused of being fraudulent at various times, including Archaeopteryx, peppered moth melanism, and Darwin's finches; these claims have been subsequently refuted. It has also been claimed that certain former pieces of evidence for evolution which are now considered out-of-date and erroneous, such as Ernst Haeckel's 19th-century comparative drawings of embryos, used to illustrate his recapitulation theory ("ontogeny recapitulates phylogeny"), were not merely errors but frauds. Molecular biologist Jonathan Wells criticizes biology textbooks by alleging that they continue to reproduce such evidence after it has been debunked. In response, the National Center for Science Education notes that none of the textbooks reviewed by Wells makes the claimed error, as Haeckel's drawings are shown in a historical context with discussion about why they are wrong, and the accurate modern drawings