To what are greater body size and facial gracility documented in homo erectus likely related?

Greater body size and facial gracility documented in Homo erectus are likely related to changes in tool technology and increasing access to meat and other proteins. Homo erectus walked just like a modern human, with traits like double arches and adducted big toe, they had a cranial capacity range from 650 cc to 1,200 cc. 

Idon't know how to do this but maybe ask your mom or dad