"On the Origin of Species" was written by British naturalist Charles Darwin. It was first published in 1859 and is considered one of the most influential scientific works ever written. The book presents Darwin's theory of evolution by natural selection, which suggests that species gradually change over time as a result of environmental pressures, and that the ones best adapted to their environment are more likely to survive and reproduce. The theory challenged traditional religious and philosophical views of the time and sparked a great deal of controversy. However, it also revolutionized the field of biology and helped lay the groundwork for many modern scientific disciplines.