You have just hit upon one of the contraversial issues among anthropologists... I suspect both Neanderthal & Sapien evolved from Homo Erectus. It is my opinion that egaster & heidelbergensis were erectus or just possibly subspecies of erectus, but erectus nonetheless.
"Homo ergaster is one of the more problematic of somewhat accepted species designations currently tossed around in anthropological literature. Each individual researcher that sees ergaster as a valid taxon sees different specimens as belonging or not belonging to the taxon. Many researchers deny any validity to the species at all. On the whole though, most researchers see too little difference between ergaster and erectus to form the basis of a species of the former, separated from the latter. As a general rule of thumb, one can consider most attributed ergaster specimens to be early erectus geographically confined to Africa (however, this is not a hard and fast rule)." (link to quote below)
Try this link, but like all links it could be wrong on this issue so I could give you 1/2 dozen with differing opinions.
http://www.archaeologyinfo.com/species.htm
My view is that erectus was an evolving species that spun off a number of subspecies as it migrated from Africa through Europe & Asia. While Australian natives & northern Europeans are obviously the same species... some would be tempted to classify them as differing species if they had only fossil evidence.
You have just hit upon one of the contraversial issues among anthropologists... I suspect both Neanderthal & Sapien evolved from Homo Erectus. It is my opinion that egaster & heidelbergensis were erectus or just possibly subspecies of erectus, but erectus nonetheless.
"Homo ergaster is one of the more problematic of somewhat accepted species designations currently tossed around in anthropological literature. Each individual researcher that sees ergaster as a valid taxon sees different specimens as belonging or not belonging to the taxon. Many researchers deny any validity to the species at all. On the whole though, most researchers see too little difference between ergaster and erectus to form the basis of a species of the former, separated from the latter. As a general rule of thumb, one can consider most attributed ergaster specimens to be early erectus geographically confined to Africa (however, this is not a hard and fast rule)." (link to quote below)
Try this link, but like all links it could be wrong on this issue so I could give you 1/2 dozen with differing opinions.
http://www.archaeologyinfo.com/species.htm
My view is that erectus was an evolving species that spun off a number of subspecies as it migrated from Africa through Europe & Asia. While Australian natives & northern Europeans are obviously the same species... some would be tempted to classify them as differing species if they had only fossil evidence.