Think of the single figure at the top of a family tree, with every line on the page running down and out from that one point. Whatever sits at that point is a progenitor. The word keeps the shape of the tree and changes what is standing at the top: a forefather, the first person to have an idea, or an old machine that every later model branched from.
From the word’s history
From Latin prōgenitor, on prōgignere, to beget, from prō- (forth) plus gignere (to beget); into English through Anglo-Norman and Middle French. By parts, pro- plus genitor, the one who begets first.
依證據裡的詞源，progenitor 來自拉丁文 prōgenitor，底下是 prōgignere（生出），由 prō-（往前、在先）加 gignere（生）組成，再經盎格魯諾曼語和中古法文進入英文；拆字就是 pro-＋genitor，「先生下來的那一位」。族譜頂端那個點的畫面，字面上本來就在。
Wiktionary entry for progenitor (source_ref kaikki:3f6f69a190036ae4:689122946), etymology_text supplied in the evidence packet
登入就可以看每一支怎麼連回核心畫面。