ancestor意为祖宗祖先(动物的)原种(机器的)原型
forefather意为祖先，祖宗(尤指男性)
Ancestor 除了指人还可以指物品，如：
Eohippus was an ancestor of the horse the progenitors of italian lyric verse forms were those used by the troubadours of provence.
forefather 只能指人，常被用于复数形式，在诗歌里 forefather 是被用得最多的，它指强烈的家庭和种族感情，或持续地定居在一个地方
