Origin of life
Further information: Abiogenesis and RNA world hypothesis
The origin of life is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens does not depend on understanding exactly how life began.[213] The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions, but it is unclear how this occurred.[214] Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any last universal common ancestor or ancestral gene pool.[215][216] Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as RNA,[217] and the assembly of simple cells.[218]