In paleoanthropology, the recent African origin of modern humans, also called the "Out of Africa" theory (OOA), recent single-origin hypothesis (RSOH), replacement hypothesis, or recent African origin model (RAO), is the dominant model of the geographic origin and early migration of anatomically modern humans (Homo sapiens). It follows the early expansions of hominins out of Africa, accomplished by Homo erectus and then Homo neanderthalensis.

The model proposes a "single origin" of Homo sapiens in the taxonomic sense, precluding

parallel evolution in other regions of traits considered anatomically modern, but not precluding multiple admixture between H. sapiens and archaic humans in Europe and Asia. H. sapiens most likely developed in the Horn of Africa between 300,000 and 200,000 years ago. The "recent African origin" model proposes that all modern non-African populations are substantially descended from populations of H. sapiens that left Africa after that time.

There were at least several "out-of-Africa" dispersals of modern humans, possibly beginning as early as 270,000 years ago, including 215,000 years ago to at least Greece, and certainly via northern Africa and the Arabian Peninsula about 130,000 to 115,000 years ago. These early waves appear to have mostly died out or retreated by 80,000 years ago.The most significant "recent" wave out of Africa took place about 70,00050,000 years ago, via the so-called "Southern Route", spreading rapidly along the coast of Asia and reaching Australia by around 65,00050,000 years ago, (though some researchers question the earlier Australian dates and place the arrival of humans there at 50,000 years ago at earliest, while others have suggested that these first settlers of Australia may represent an older wave before the more significant out of Africa migration and thus not necessarily be ancestral to the region's later inhabitants) while Europe was populated by an early offshoot which settled the Near East and Europe less than 55,000 years ago.In the 2010s, studies in population genetics uncovered evidence of interbreeding that occurred between H. sapiens and archaic humans in Eurasia, Oceania and Africa, indicating that modern population groups, while mostly derived from early H. sapiens, are to a lesser extent also descended from regional variants of archaic humans.

Deoxyribonucleic acid ( (listen); DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms and many viruses. DNA and ribonucleic acid (RNA) are nucleic acids. Alongside proteins, lipids and complex carbohydrates (polysaccharides), nucleic acids are one of the four major types of macromolecules that are essential for all known forms of life.

The two DNA strands are known as polynucleotides as they are composed of simpler monomeric units called nucleotides. Each nucleotide is composed of one of four nitrogen-containing nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]), a sugar called deoxyribose, and a phosphate group. The nucleotides are joined to one another in a chain by covalent bonds (known as the phospho-diester linkage) between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone. The nitrogenous bases of the two separate polynucleotide strands are bound together, according to base pairing rules (A with T and C with G), with hydrogen bonds to make double-stranded DNA. The complementary nitrogenous bases are divided into two groups, pyrimidines and purines. In DNA, the pyrimidines are thymine and cytosine; the purines are adenine and guanine.

Both strands of double-stranded DNA store the same biological information. This information is replicated when the two strands separate. A large part of DNA (more than 98% for humans) is non-coding, meaning that these sections do not serve as patterns for protein sequences. The two strands of DNA run in opposite directions to each other and are thus antiparallel. Attached to each sugar is one of four types of nucleobases (or bases). It is the sequence of these four nucleobases along the backbone that encodes genetic information. RNA strands are created using DNA strands as a template in a process called transcription, where DNA bases are exchanged for their corresponding bases except in the case of thymine (T), for which RNA substitutes uracil (U). Under the genetic code, these RNA strands specify the sequence of amino acids within proteins in a process called translation.

Within eukaryotic cells, DNA is organized into long structures called chromosomes. Before typical cell division, these chromosomes are duplicated in the process of DNA replication, providing a complete set of chromosomes for each daughter cell. Eukaryotic organisms (animals, plants, fungi and protists) store most of their DNA inside the cell nucleus as nuclear DNA, and some in the mitochondria as mitochondrial DNA or in chloroplasts as chloroplast DNA. In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm, in circular chromosomes. Within eukaryotic chromosomes, chromatin proteins, such as histones, compact and organize DNA. These compacting structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed.