Edict of Milan is a proclamation that permanently established religious toleration for Christianity within the Roman Empire.

Mesopotamian southern region is desert, but the rivers Euphrates and Tigris support the city life here. These rivers deposit their silt by flooding in the region and make the soil fertile. When the river Euphrates enters the desert, it gets divided into small channels. These river channels provided irrigation facilities in the past. Crops such as wheat, barley, peas or lentils were grown here, though there did not happen sufficient rainfall. In the north-east region, sheepary goats were grazed on steppe by the Mesopotamians. In this region milk, wool and meat was produced in bulk. Fish was also available in plenty. Date-palm provided fruit in summer. Considering these facts we can conclude that these regions were of utmost importance for Mesopotamians.

The Replacement Model supports the view that the modem human beings originated in a single region, i.e. Africa. In support of this view, most of the scholars tried to correlate the anatomical and genetic similarity of modern humans. It indicates that their ancestors belonged to one region and from where they migrated to different parts of the world.
The Regional Continuity Model supports the view that modern humans originated at several regions across Africa, Asia and Europe. To support their view the scholars tried to correlate the anatomical differences of modem humans which indicate that they belonged to different regions.

Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa.

An ice age is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth is currently in the Quaternary glaciation, known in popular terminology as the Ice Age.  Individual pulses of cold climate are termed "glacial periods" (or, alternatively, "glacials", "glaciations", or "glacial stages", or colloquially, "ice ages"), and intermittent warm periods are called "interglacials", with both climatic pulses part of the Quaternary or other periods in Earth's history.

In the terminology of glaciology, ice age implies the presence of extensive ice sheets in both northern and southern hemispheres. By this definition, we are in an interglacial period—the Holocene. The amount of heat trapping gases emitted into Earth's Oceans and atmosphere will prevent the next ice age, which otherwise would begin in around 50,000 years, and likely more glacial cycles.

Regional continuity model belongs to human origin assets that is consider by modern Homo sapiens and developed from different regional populations.
This includes archaic homo sapiens that includes previously evolved from regional populations of erectus.
The replacement continuity delivers partial theory and includes fact that these homo sapiens are migrated out Africa and into Europe and Asia.