The fossil is the most complete pre-human skull uncovered. With other partial remains previously found at the rural site, it gives researchers the earliest evidence of human ancestors moving out of Africa and spreading north to the rest of the world, according to a study published Thursday in the journal Science.

The skull and other remains offer a glimpse of a population of pre-humansof 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.

Nearly all of the previous pre-human discoveries have been fragmented bones, scattered over time and locations — like a smattering of random tweets of our evolutionary history. The findings at Dmanisi are more complete, weaving more of a short story. Before the site was found, the movement from Africa was put at about 1 million years ago.