Oppenheimer trained in medicine at Oxford and London universities, qualifying in 1971. From 1972 he worked as a clinical paediatrician, mainly in Malaysia, Nepal and Papua New Guinea. He carried out and published clinical research in the areas of nutrition, infectious disease (including malaria), and genetics, focussing on the interactions between nutrition, genetics and infection, in particular iron nutrition, thalassaemia and malaria. From 1979 he moved into medical research and teaching, with positions at the Liverpool School of Tropical Medicine, Oxford University, a research centre in Kilifi, Kenya and the Universiti Sains Malaysia in Penang. He spent three years undertaking fieldwork in Papua New Guinea, studying the effects of iron supplementation on susceptibility to infection. His fieldwork, published in the late 1980s, identified the role of genetic mutation in malarious areas as a result of natural selection due to its protective effect against malaria, and that different genotypes for alpha-thalassaemia traced different migrations out to the Pacific. Following that work, he concentrated on researching the use of unique genetic mutations as markers of ancient migrations.

From 1990 to 1994 Oppenheimer served as chairman and chief of clinical service in the Department of Paediatrics in the Chinese University of Hong Kong. He worked as senior specialist paediatrician in Brunei from 1994 to 1996. He returned to England in 1997, writing the book Eden in the East: the drowned continent of Southeast Asia, published in 1998. The book synthesised work across a range of disciplines, including oceanography, archaeology, linguistics, social anthropology and human genetics. He continued to write books and articles, and began a second career as a researcher and popular-science writer on human prehistory. He worked as consultant on two television documentary series, The Real Eve (Discovery Channel) and Out of Eden (Channel 4), and published a second book, Out of Eden: the Peopling of the World (retitled The Real Eve in USA). This was followed in 2006 by The Origins of the British: a genetic detective story, on the post-glacial peopling of Great Britain and Ireland. In 2009 he was consultant on the BBC TV series The Incredible Human Journey.

• Eden in the East. 1999, Phoenix (Orion) ISBN 0-7538-0679-7
• Out of Eden. 2004, Constable and Robinson ISBN 1-84119-894-3 UK title of The Real Eve.
• The Real Eve. Carroll & Graf; (September 9, 2004) ISBN 0-7867-1334-8 US title of Out of Eden.
• The Origins of the British - A Genetic Detective Story. 2006, Constable and Robinson. ISBN 1-84529-158-1.

Eden in the East

In his book Eden in the East: The Drowned Continent of Southeast Asia, published in 1998, Oppenheimer hypothesizes that Eurasians have southeast Asian origins, citing evidence from a variety of disciplines to make his case: geology, archaeology, genetics, linguistics, and folklore. Using geological evidence, he writes about the rise in ocean levels that accompanied the waning of the ice age...as much as 500 feet...during the period 14,000-7,000 years ago and says that this submerged the continental shelf off the coast of southeast Asia. He, and others, calls this submerged continent Sundaland and cites archaeological evidence for an original culture in this region. The rising ocean levels caused this culture to disperse, and Oppenheimer supports this idea with the above-mentioned evidence from genetics, linguistics, and folklore. He notes, for example, that those cultures in regions whose geology would have led to their being submerged have flood myths, whereas there are no flood myths in Africa, which because of its lack of a continental shelf, was relatively unaffected by the rising ocean level.

The Real Eve (documentary and US book title) / Out of Eden (UK book title)

In 2002, Oppenheimer worked as consultant on a television documentary series, The Real Eve, produced by the American cable TV network the Discovery Channel and directed by Andrew Piddington. The series was known as Where We Came From in the United Kingdom.The "Eve" in the title refers to Mitochondrial Eve, a name used for the most recent common ancestor of all humans in the matrilineal (mother to daughter) line of descent.

Following the series, Oppenheimer published a book on the same theme, originally titled Out of Eden in the UK and republished as The Real Eve in the US. This work, published in 2004, focuses on Oppenheimer's hypothesis that modern humans emerged from East Africa in a single major exodus numbering no more than a few hundred individuals. This lone group of wanderers, he suggests, became the ancestors of all non-Africans, their descendants having since radiated into a plurality of physical characteristics, languages, ethnicities and cultures as seen today.

Origins of the British

In his 2006 book The Origins of the British, revised in 2007, Oppenheimer argued that neither Anglo-Saxons nor Celts had much impact on the genetics of the inhabitants of the British Isles, and that British ancestry mainly traces back to the Palaeolithic Iberian people, now represented best by Basques, instead. He also argued that the Scandinavian input has been underestimated. He published an introduction to his book in Prospect magazine and answered some of his critics in a further Prospect magazine article in June 2007.

Oppenheimer uses genetic studies to give an insight into the genetic origins of people in the British Isles and speculates on how to match this evidence with documentary, linguistic and archaeological data to give insights into the origins of Britain, the Celts, the Vikings and the English. Oppenheimer uses DNA databases provided by Weale et al., Capelli et al. and Rosser et al. to provide new analyses of the haplotype distributions in both the male and female lines of the populations of Britain and Ireland (as well as Western Europe).

He breaks down the R1b haplogroup into a detailed set of "clans" that are undefined.

He makes the case that the geography and climate have had an influence on the genetics and culture of Britain, because of coastline changes. These genetic and cultural changes stem from two main zones of contact:

1. The Atlantic fringe, mainly from Spain and Portugal, to the western British Isles
2. Northern Europe, originally across Doggerland to eastern England and from Scandinavia to northern Scotland

Oppenheimer derives much archaeological information from Professor Barry Cunliffe's ideas of the trading routes using the Atlantic from Spain, and from the writings of:

• Simon James (The Atlantic Celts - Ancient People or Modern Invention? ISBN 0299166740)
• Francis Pryor (Britain B.C. : life in Britain and Ireland before the Romans ISBN 0007126921)
• John Collis (The Celts : origins, myths & inventions ISBN 0752429132)
• Colin Renfrew, (Archaeology and Language - The Puzzle of Indo-European Origins ISBN 0521354323)

The work of the geneticist Peter Forster has strongly influenced Oppenheimer's linguistic theories. From Forster's evidence that the Germanic genetic contribution to eastern England originated before the Anglo-Saxon conquest, Oppenheimer argues for the possibility that some inhabitants of the isle of Britain spoke English well before the so-called "Dark Ages".

Oppenheimer's main ideas include:

1. The importance of Cunliffe's Atlantic routes to the settling of Britain.
2. Since much British genetic material dates to the re-settlement of Britain following the ice ages, all subsequent invasions/migrations/immigrations occurred on a relatively small scale and did not replace Britain's population.
3. The origins of Celtic culture lie in southwestern Europe. The Central European ([La Tène culture]) theory for Celtic origins has no basis. Celtic culture arrived in the British Isles before the Iron Age and only involved limited movement of people, mainly into the east of England.
4. There are some differences between the male and female origins of the British population, but these are small.
5. Some genetic evidence is in support of Renfrew's theory that Indo-European origins comes with farming.
6. Genetic evidence suggests that the division between the West and the East of England does not begin with the Anglo-Saxon invasion but originates with two main routes of genetic flow ... one up the Atlantic coast, the other from neighbouring areas of Continental Europe. This happened just after the Last Glacial Maximum. There is a cline between east and west, rather than a sharp division.
7. Scandinavian influences, stronger than suspected, may outweigh West Germanic influence.
8. A genetic difference exists between the Saxon areas of England and the Anglian areas. (Oppenheimer suggests that the so-called Anglo-Saxon invasion actually mostly consisted of an Anglian incursion.)
9. English being native to east Britain might explain the lack of Celtic influence on early English and the genetic split between East and West.
10. Classical sources differentiate between Gallic/Celtic and Belgae. Sources state that some of the (northern) Belgae have a German origin. Various archaeological and linguistic evidence make for a weaker case for Celtic presence in Belgium and Eastern England than in Gallic/Celtic or western Britain.

In Origins of the British (2006), Stephen Oppenheimer states (pages 375 and 378):

"By far the majority of male gene types in the British Isles derive from Iberia (Spain and Portugal), ranging from a low of 59% in Fakenham, Norfolk to highs of 96% in Llangefni, north Wales and 93% Castlerea, Ireland. On average only 30% of gene types in England derive from north-west Europe. Even without dating the earlier waves of north-west European immigration, this invalidates the Anglo-Saxon wipeout theory..."

"...75-95% of British Isles (genetic) matches derive from Iberia... Ireland, coastal Wales, and central and west-coast Scotland are almost entirely made up from Iberian founders, while the rest of the non-English parts of the British Isles have similarly high rates. England has rather lower rates of Iberian types with marked heterogeneity, but no English sample has less than 58% of Iberian samples..."

In page 367 Oppenheimer states in relation to Zoë H Rosser's pan-European genetic distance map:

"In Rosser's work, the closest population to the Basques is in Cornwall, followed closely by Wales, Ireland, Scotland, England, Spain, Belgium, Portugal and then northern France."

He reports work on linguistics by Forster and Toth which suggests that Indo-European languages began to fragment some 10,000 years ago (at the end of the Ice Age). Oppenheimer claims that Celtic split from Indo-European earlier than previously suspected, some 6000 years ago, while English split from Germanic before the Roman period, see Forster, Polzin and Rohl.