... The researchers looked at the skulls of 27 women and 28 men who died in Lisbon, Portugal, between 1880 and 1975. They also evaluated the skulls of 40 women and 39 men who died between 1895 and 1903 in the rural area of Coimbra, just over 120 miles north of Lisbon.

The researchers found significant variation between female skulls from Lisbon and those from Coimbra. "The differences were in the shape of the skull, not the size," says Dr. Ann Ross, professor of anthropology at NC State and co-author of a paper describing the study. ...
They're attributing the difference to genetics

Study finds significant skull differences between closely linked groups