"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.