Stack Exchange
TikZ Tree Structure and Genealogytree (or alternatives)
I'm attempting to draw the following "idea genealogy" using TikZ for use in a presentation:

and based off a prior answer, I have the following solution.
\documentclass[10pt]{standalone}

\usepackage[sfdefault]{FiraSans}
\usepackage[T1]{fontenc}
\renewcommand*\oldstylenums[1]{{\firaoldstyle #1}}

\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[scale=0.50,node distance=20mm,every node/.style={rectangle,minimum height=10mm,text width=17mm,align=center,rounded corners=1mm,draw=black,fill={rgb:red,1;green,2;blue,5},fill opacity=0.2,text opacity=1}]
    \node at (0,0)                         (ko) {Kowalski};
    \node[above of=ko,node distance=40mm]  (le) {Leibniz};
    \node[above of=le,xshift=10mm]         (ar) {Aristotle};
    \node[left of=ar]                      (ch) {Chrysippus};
    \node[right of=ko]                     (co) {Colmerauer};
    \node[above of=co]                     (po) {Post};
    \node[left of=ko]                      (mc) {McCarthy};
    \node[above of=mc]                     (ta) {Tarski};
    \node[left of=mc]                      (mi) {Minski};
    \node[left of=ta,node distance=30mm]   (fr) {Frege};
    \node[above of=fr]                     (bo) {Boole};
    \node[below of=co,xshift=-5mm,fill=green!50!black] (pr) {Prolog};
    \node[below of=pr]                     (cl) {Clark};
    \node[below of=mc,xshift=12mm]         (mo) {Moore};
    \node[below of=mc,xshift=-12mm]        (re) {Reiter};
    \node[left of=re]                      (do) {McDermott Doyle};
    \node[below of=mc,node distance=40mm]  (ge) {Gelfond Lifschitz};
    \node[below of=ge,fill=green!50!black]   (ap) {A-Prolog};

    \foreach \x/\y in {ar/le,ch/le,le/ko,po/ko,po/co,bo/fr,fr/ta,ta/mi,ta/mc,ta/ko,mc/do,mc/re,mc/mo,mc/ge,mo/ge,ko/pr,co/pr,pr/cl,pr/ge,cl/ge,ge/ap}
    \draw[-stealth,shorten >=1mm] (\x) -- (\y);
\end{tikzpicture}


\end{document}

While the solution is adequate, I'm not particularly satisfied with the manual layout of the nodes, and the way the edges are styled. I was perusing the various packages for drawing trees, and would like to have something that looks like the examples given in the documentation for the genealogytree package. I'm having trouble getting started however, particularly when it comes to connecting the levels of the tree, (McCarthy to McDermott and Reiter, but also to Gelfond (who also has Moore and Prolog) as ancestors.
Is there anyone that can help me get started?

Most packages for drawing trees are intended for trees in the strict sense, where no child has more than one parent and there's a single root. The genealogytree package is obviously intended for trees in another sense, but will assume no child has more than two parents. (Arguably, this is behind-the-times, but it is traditional.) The graphs stuff in TikZ might be more helpful. (This includes trees, but isn't limited to them.) Some of it needs LuaTeX, but not all.

Actually, you can add as many parents as you want with genealogytree. I made an attempt with 10 parents and it works but I am sure you can add more if needed.
