Savannah Ancestry
Savannah Ancestry
[Cueball and Megan are at a blackboard with equations and graphs on it.] Cueball: Look, I'm doing my best, but the fact is your savannah ancestors just didn't prepare you for doing abstract math. Megan: See, that's just the kind of bullshit sexism that discredits evo-psych. Your "evolutionary histories" always seem tuned to produce 1950's gender roles. Cueball: Evolutionary? What? I meant Savannah, Georgia. Megan: ...Hey! Let's leave my mom out of this.

Savannah ancestry usually means our ancestors in the African savanna , millions of years ago.
Evo-psych means evolutionary psychology .
Cueball is apparently trying to teach Megan something mathematical, feels frustrated at his lack of success, blames that lack of success entirely on his student, and appears to use evolutionary psychology, specifically a popular trope/myth about women being bad at abstract thinking, as an excuse. Evolutionary excuses in this context are trying to lay blame somewhere other than either participant, and so can be seen as comforting, but of course they falsely place all women in an inferior position to all men, at least when it comes to "abstract math". She naturally objects to the excuse, rightly calls it bullshit sexism, and, depending on how you interpret it, may indicate this isn't the first time she's heard him say something similar.
But the twist is that he turns out not to be talking about her lower-case savannah ancestors, the ones in the African savannah of eons ago, but rather of her very recent "Savannah ancestors", better called parents, who live in the city of Savannah, Georgia, USA . They apparently know each other well. The implication is now much more personal: that her mother didn't prepare her. Of course, Randall uses only upper case everywhere, so he has avoided giving the reader a clue about the misdirect-joke he is working toward.
Teasing people about their mothers in the USA, specifically about their mothers' stupidity or fatness, is a common enough theme in popular culture that there is a series of jokes that start with the words "Yo mama" that exemplify the genre. There is also an extremely common theme that the South's education system is failing; the comic combines the two.
The title text is apparently Megan starting to defend her mother, but then lapsing into a Yo Mama joke without the introducing words, showing that her mother is stupid enough to think that a quarterback (one of the positions played in American football) would be a river in Egypt. This is a conflation of the Yo Mama joke "Yo mama so stupid she thinks a quarterback is a refund!" and the common pun, "Denial (sounds like "The Nile") is not just a river in Egypt".
[Cueball and Megan are at a blackboard with equations and graphs on it.] Cueball: Look, I'm doing my best, but the fact is your savannah ancestors just didn't prepare you for doing abstract math. Megan: See, that's just the kind of bullshit sexism that discredits evo-psych. Your "evolutionary histories" always seem tuned to produce 1950's gender roles. Cueball: Evolutionary? What? I meant Savannah, Georgia. Megan: ...Hey! Let's leave my mom out of this.
