evidence: - California State University, Sacramento - Survival of the fittest molecule survival of the fittest, term made famous in the fifth edition (published in 1869) of On the Origin of Species by British naturalist Charles Darwin, which suggested that organisms best adjusted to their environment are the most successful in surviving and reproducing. Darwin borrowed the term from English sociologist and philosopher Herbert Spencer, who first used it in his 1864 book Principles of Biology. (Spencer came up with the phrase only after reading Darwin’s work.) [...] Darwin did not consider the process of evolution as the survival of the fittest; he regarded it as survival of the fitter, because the "struggle for existence" (a term he took from English economist and demographer Thomas Malthus) is relative and thus not absolute. Instead, the winners with respect to species within ecosystems could become losers with a change of circumstances. For example, fossil evidence supports the notion that the mammoth (Mammuthus) was more fit during the most recent ice age (which ended roughly 11,700 years ago), but it became less fit as humans hunted it and the world’s climate warmed; fossil evidence suggests that the mammoth succumbed to extinction a few thousand years later.