DMANISI, Georgia — The discovery of a 1.8-million-year-old skull is giving researchers new insights into early human evolution.

The fossil was found buried under a medieval village in Georgia and is the most complete pre-human skull uncovered. Along with partial remains previously found at the rural site, researchers say it provides the earliest evidence of human ancestors moving out of Africa and spreading north to the rest of the world.

Together, the fossils reveal a population of pre-humans of various sizes living at the same time — something that scientists had not seen before for such an ancient era. This diversity bolsters one of two competing theories about the way our early ancestors evolved — spreading out more like a tree than a bush.

The discovery was described Thursday in the journal Science.