With their camp threatened by a murderous tiger, Jane sees a chance for gender equality, while Gary invents - underwear. Also, they discover fire.

After an elk saves his life, Ugg experiments with being a vegetarian. No one cares. Especially Gary and Trog, who are busy defining their relationship.

Gary sets out to define humanity's first relationship, while Minerva tries to arm everyone in the camp with spears.

For the first time in history, the camp has the morning off from hunting and gathering. The possibilities for human achievement are endless. So they discover alcohol and get hammered.

After falling into the comfort of their relationship, a near-death experience makes Jane and Gary wonder if comfort is a good thing. Trog, sees his reflection in the world's first mirror and is not pleased by his appearance.

Jane and Gary host the world's first exclusive party. But when a mysterious stranger collapses in their cave, the camp must address what it means to belong.

In an effort to find a low-key, relaxing activity, Gary invents the first sport. Which leads the camp to discover competition, anger, divisiveness, and of course, violence.

Gary contracts a fatal rash, forcing him to confront his mortality. As expected, he deals with it maturely, demanding everyone in camp celebrate his legacy at the world's first funeral.

After a rainstorm soaks the campsite, Jane leads a group, including a woefully unprepared Gary, on a dangerous quest to find dry wood. This leaves Marsh with a captive audience, and a chance to share the greatest story ever told.

Upset he's not rewarded for inventing the wheel, Trog sets out to profit from his discovery, accidentally inventing the modern economy. Gary and Jane become poor immediately.