Views on the origin and diversity of living things

How the first living thing arose from non-living matter is one of the biggest open questions in biology. Some building blocks of life have been produced in the laboratory, but no laboratory has produced a living cell from non-living matter. Proposed models include the "RNA world", deep-sea hydrothermal vents and life arriving from space (panspermia). Religions attribute life to God's creation.

Lamarck argued that living things become more complex over time and that the development of an organ through use, or its withering through disuse, is passed to offspring. This view was largely abandoned in the 20th century. Recent work on epigenetic inheritance has led some researchers to discuss Lamarck again.

Darwin and Wallace independently arrived at the idea that individuals of a species differ in heritable ways, that those better suited to their surroundings leave more offspring, and that species therefore change and diverge over time. Darwin published "On the Origin of Species" in 1859. Darwin himself recorded the scarcity of intermediate forms in the fossil record as one of the main difficulties facing his theory.

In the 1930s and 1940s Darwin's natural selection and Mendelian genetics were united through mathematical population genetics. In this framework evolution is the change of gene frequencies in populations through mutation, selection, drift and migration. In 1942 Julian Huxley named this union the "modern synthesis".

Creationism holds that living species (or basic "kinds") were created directly and separately by God. Young-earth creationism, based on a literal reading of scripture, holds that the Earth is a few thousand years old; old-earth creationism accepts geological ages but maintains that species were created separately. In Turkey, too, creationism has been advocated in widely circulated publications, especially since the 1990s.

Kimura proposed that most changes at the molecular level (in DNA and protein sequences) arise not by selection but by the random spread (genetic drift) of mutations that are neither beneficial nor harmful. The theory arose as a challenge to the role of Darwinian selection at the molecular level. Debates about how pervasive selection is continue today.

Eldredge and Gould argued that in the fossil record species remain almost unchanged for long periods (stasis), and that change happens in geologically short bursts associated with speciation. In their view the scarcity of intermediate forms reflects the real tempo of evolution rather than gaps in the record. The idea was debated as a challenge to Darwin's notion of slow, gradual change.

According to proponents of intelligent design, some biological structures are so complex that they would not work at all if one part were missing ("irreducible complexity"). They therefore infer that such structures were produced by an intelligent designer rather than by blind, step-by-step processes. Opponents present models showing the stepwise development of these structures and argue that the theory is not scientifically testable. In 2005 a US court held that teaching it as science in public schools was unconstitutional.

According to theistic evolution, God created living things through the evolutionary processes that science describes, and no conflict is seen between science and religion. Francis Collins, former director of the Human Genome Project, and the Catholic Church's official statement of 1996 are examples. Both atheist scientists and creationists criticise the view, for different reasons.

A group of biologists argues that developmental processes, environment-dependent changes in form, epigenetic inheritance and organisms' modification of their own surroundings (niche construction) play a larger role in directing evolution than assumed, and that the current theory should therefore be extended. Other biologists argue that these phenomena are already accommodated within the existing theory.

There is no single view on the origin of living things in the Muslim world. Some authors see precursors of evolutionary ideas in the works of al-Jāḥiẓ and Ibn Khaldūn; others argue this projects modern concepts onto the past. Today views range from creationism, holding that species were created separately, through a view that exempts only Adam and Eve, to theistic evolution without exceptions.