There was no--zero--evidence of Hebrew slavery, nor any other kind of slavery, in ancient Egypt: historical, archeological, anthropological, philological, cultural, nor biological. The story in the Bible is a metaphor.
http://www.haaretz.com/mobile/were-jews-ever-really-slaves-in-egypt-or-is-passover-a-myth-1.420844?v=A7693F23035E2643BD7AD82DA9653876