Ancient DNA in the context of "Polymerase chain reaction"

The genetic history of Sardinia consists of the study of the gene pool of the Sardinian people with two main objectives. The first is purely cultural and is to reconstruct the natural history of the population. The other instead has the aim of understanding the genetic causes of high life expectancy and of some pathologies by exploiting some peculiarities of the Sardinian population.

The geographical position of Sardinia and the mountainousness of its territory have meant that particular anthropological and genetic characteristics have been created in the Sardinian population, due to phenomena such as isolation, endogamy and evolutionary processes such as genetic drift, in similarly to other European populations such as the Basques, Sámi and Icelanders.

The Proto-Indo-European homeland was the prehistoric homeland of the Proto-Indo-European language (PIE), meaning it was the region where the proto-language was spoken before it split into the dialects from which the earliest Indo-European language later evolved.

The most widely accepted proposal about the location of the Proto-Indo-European homeland was called the steppe hypothesis. It puts the archaic, early, and late PIE homeland in the Pontic–Caspian steppe around 4000 BCE. A notable second possibility, which has gained renewed attention during the 2010s and 2020s due to aDNA research, is the Armenian hypothesis, which situates the homeland for archaic PIE ('Indo-Hittite') south of the Caucasus mountains. A third contender is the Anatolian hypothesis, which puts it in Anatolia c. 8000 BCE. Several other explanations have been proposed, including the outdated but historically prominent North European hypothesis, the Neolithic creolisation hypothesis, the Paleolithic continuity paradigm, the Arctic theory, and the "indigenous Aryans" (or "out of India") hypothesis. These are not widely accepted, and are considered to be fringe theories.

Paleogenetics is the study of the past through the examination of preserved genetic material from the remains of ancient organisms. Emile Zuckerkandl and Linus Pauling introduced the term in 1963, long before the sequencing of DNA, in reference to the possible reconstruction of the corresponding polypeptide sequences of past organisms. The first sequence of ancient DNA, isolated from a museum specimen of the extinct quagga, was published in 1984 by a team led by Allan Wilson.

Paleogeneticists do not recreate actual organisms, but piece together ancient DNA sequences using various analytical methods. Fossils are "the only direct witnesses of extinct species and of evolutionary events" and finding DNA within those fossils exposes tremendously more information about these species, potentially their entire physiology and anatomy.

Archaeogenetics is the study of ancient DNA using various molecular genetic methods and DNA resources. This form of genetic analysis can be applied to human, animal, and plant specimens. Ancient DNA can be extracted from various fossilized specimens including bones, eggshells, and artificially preserved tissues in human and animal specimens. In plants, ancient DNA can be extracted from seeds and tissue. Archaeogenetics provides us with genetic evidence of ancient population group migrations, domestication events, and plant and animal evolution. The ancient DNA cross referenced with the DNA of relative modern genetic populations allows researchers to run comparison studies that provide a more complete analysis when ancient DNA is compromised.

Archaeogenetics receives its name from the Greek word arkhaios, meaning "ancient", and the term genetics, meaning "the study of heredity". The term archaeogenetics was conceived by archaeologist Colin Renfrew.

Neanderthal genetics testing became possible in the 1990s with advances in ancient DNA analysis. In 2008, the Neanderthal genome project published the full sequence Neanderthal mitochondrial DNA (mtDNA), and in 2010 the full Neanderthal genome. Genetic data is useful in testing hypotheses about Neanderthal evolution and their divergence from early modern humans, as well as understanding Neanderthal demography, and interbreeding between archaic and modern humans.

Modern humans and Neanderthals had multiple different interbreeding episodes, but Neanderthal-derived genes in the present-day human genome descends from an episode 250,000 years ago probably in Eurasia, and 47,000 to 65,000 years ago in the Near East. While 20% of the Neanderthal genome survives today, most people only carry about a few percentage points of Neanderthal DNA, and most Neanderthal-derived DNA is non-coding. Neanderthals maintained a low genetic diversity and suffered from inbreeding depression; consequently most Neanderthal genes were probably selected out of the gene pool. Barring hybrid incompatibility or negative selection, most Neanderthal DNA may descend from the children of modern human females and Neanderthal males. Neanderthals also interbred with Denisovans in the Siberian Altai Mountains.

Panthera spelaea, commonly known as the cave lion (or less commonly as the steppe lion), is an extinct Panthera species that was native to Eurasia and northwest North America during the Pleistocene epoch. Genetic analysis of ancient DNA has revealed that while closely related, it was a distinct species genetically isolated from the modern lion (Panthera leo), with the genetic divergence between the two species estimated at around 500,000 years ago.

The earliest fossils of the P. spelaea lineage (either regarded as the separate species Panthera fossilis or the subspecies P. spelaea fossilis) in Eurasia date to around 700,000 years ago (with possible late Early Pleistocene records). It is closely related and probably ancestral to the American lion (Panthera atrox). The species ranged from Western Europe to eastern Beringia in North America, and was a prominent member of the mammoth steppe fauna, and an important apex predator across its range along with other large carnivores like cave hyenas, which cave lions came into conflict with.