The history of pseudoscience is the study of pseudoscientific theories over time. A pseudoscience is a set of ideas that presents itself as science, while it does not meet the criteria to properly be called such. Distinguishing between proper science and pseudoscience is sometimes difficult. One popular proposal for demarcation between the two is the falsification criterion, most notably contributed to by the philosopher Karl Popper. In the history of pseudoscience it can be especially hard to separate the two, because some sciences developed from pseudosciences. An example of this is the science chemistry, which traces its origins from the protoscience of alchemy. The vast diversity in pseudosciences further complicates the history of pseudoscience. Some pseudosciences originated in the pre-scientific era, such as astrology and acupuncture. Others developed as part of an ideology, such as Lysenkoism, or as a response to perceived threats to an ideology. An example of this is creationism, which was developed as a response to the scientific theory of evolution. Despite failing to meet proper scientific standards, many pseudosciences survive. This is usually due to a persistent core of devotees who refuse to accept scientific criticism of their beliefs, or due to popular misconceptions. Sheer popularity is also a factor, as is attested by astrology which remains popular despite being rejected by a large majority of scientists. 19th century Among the most notable developments in the history of pseudoscience in the 19th century are the rise of Spiritualism (traced in America to 1848), homeopathy (first formulated in 1796), and phrenology (developed around 1800). Another popular pseudoscientific belief that arose during the 19th century was the idea that there were canals visible on Mars. A relatively mild Christian fundamentalist backlash against the scientific theory of evolution foreshadowed subsequent events in the 20th century. The study of bumps and fissures in people's skulls to determine their character, phrenology, was originally considered a science. It influenced psychiatry and early studies into neuroscience. As science advanced, phrenology was increasingly viewed as a pseudoscience. Halfway through the 19th century, the scientific community had prevailingly abandoned it, although it was not comprehensively tested until much later. Halfway through the century, iridology was invented by the Hungarian physician Ignaz von Peczely. The theory would remain popular throughout the 20th century as well. Spiritualism (sometimes referred to as "Modern Spiritualism" or "Spiritism") or "Modern American Spiritualism" grew phenomenally during the period. The American version