"Homo antecessor" and "H. heidelbergensis" may have had the same ancestor: "Homo ergaster" from Africa. Mostly, "H. ergaster" was not very different from "H. heidelbergensis". However, "H. heidelbergensis" had a larger brain-case. On average, their skulls had a volume of 1100 – 1400 cm³ of space inside. (The average modern human has 1350 cm³ of space inside his or her skull.) "H. heidelbergensis" also had more advanced tools and behavior than "H. ergaster". For these reasons, H. heidelbergensis has been classified as a separate species.