Beginning around 1.25 million years ago, up until 700,000 years ago, the earth was undergoing a major global climatic change where glacial/interglacial cycles changed from 41,000 to 100,000 years periodicity. This is known as the Mid-Pleistocene Transition (MPT). While there are only speculations as to why or how this change happened, it has resulted in significant changes in the distribution of plant and animal communities in most parts of the world. For example, Homo heidelbergensis appears in Europe out of Africa around 800,000 years ago, together with a number of African carnivores, such as lion, leopard, and spotted hyaena, and other large mammals. It is about the same time that the Acheulean stone tool technology also seems to have appeared in the European archaeological record. Generally, the longer interstadial and interglacial periods may have created long warmer and temperate periods, facilitating northward expansion of Homo heidelbergensis and other populations migrating to Europe from southwest Asia and Africa.

Image credit https://onlinelibrary.wiley.com/doi/10.1002/evan.21311