Geography of Europe is not surrounded by sea and its southeastern border has always been variously defined for centuries. In terms of shape, Europe is a collection of connected peninsulas and nearby islands. The two largest peninsulas are mainland Europe and Scandinavia to the north, divided from each other by the Baltic Sea. Three smaller peninsulas—Iberia, Italy and the Balkans—emerge from the southern margin of the mainland. The Balkan peninsula is separated from Asia by the Black and Aegean Seas. Italy is separated from the Balkans by the Adriatic Sea, and from Iberia by the Mediterranean Sea, which also separates Europe from Africa.
African admixture in Europe Europe may have a common origin in Asia (e.g. Y haplogroups R1, and some paternal haplogroup T and U subclades). One subclade of haplogroup U, namely U6a1, is known to have expanded from northern and eastern Africa back into Europe even though haplogroup U6 is considered to have originated in the Middle East. Other lineages are known to have moved from Europe directly into Africa, for example mitochondrial haplogroups H1 and H3. Such bidirectional migrations between Africa and Eurasia complicate the task of defining admixture. One proposed example of Holocene gene flow from Africa to Europe, via the Middle East,