Title text:

If only my ancestors had been fortunate enough to marry into the branch of the bacteria family that could photosynthesize, like all my little green cousins here.

Transcript:

[Cueball and Beret Guy, seen from afar in silhouette, are walking up a grassy hill.]

[They continue walking up the hill, reaching its grassy summit. Now with normal lighting. Beret Guy is a bit ahead of Cueball.]
Beret Guy: I learned something today.
Beret Guy: I went on one of those family tree sites and kept clicking back, and it turns out I’m related to stromatolites!

[Closeup on Cueball. Beret Guy’s reply comes off-panel from a starburst on the right edge of the panel.]
Cueball: The bacterial mats?
Beret Guy [off-panel]: Yeah! A few billion years back, on my mitochondria’s side.

[Cueball and Beret Guy standing on the top of the grassy hill facing each other. Berety Guy holding a hand out towards Cueball.]
Beret Guy: My Archaean ancestors absorbed some bacteria that were cousins of stromatolites. That’s how I got mitochondria.
Beret Guy: Cell nuclei, too.

[Cueball is standing behind Beret Guy who is now sitting down in the grass leaning back on one arm with the other arm resting on his bent knee.]
Cueball: I think there are still living stromatolites. You could get in touch.
Beret Guy: Nah, they’re probably busy. I don’t want to bother them.

[Cueball is sitting behind Beret Guy who is now lying down, both again shown in silhouette from a far, revealing they are on the top of the grassy hill.]
Cueball: So what are you going to do with this knowledge? Nothing?
Beret Guy: Lying on a hill in the warm sun is an old family tradition.

Source: xkcd.com/3046/

explainxkcd for #3046