Cain and Abel offer the fruits of their labor, grain and sheep respectively, to God as some sort of religious observance.

FORBES: Dear President Obama: I'm Only My Brother's Keeper If My Brother Is My Sheep

They conceive and bear two sons, Cain and Abel.

FORBES: Dear President Obama: I'm Only My Brother's Keeper If My Brother Is My Sheep

To continue the interpretation, the story of Cain and Abel may be taken as an illustration of the zero-sum game of primogeniture, as well as an allegory for the slaughter of nomadic pasturage by urban agriculture.

NEWYORKER: The Sanctuary

Even such Cain-and-Abel types as Raymond Hood, a hard-drinking visionary architect, and John Todd, the authoritarian teetotaller that Rockefeller hired as his chief developer, became good business buddies.

ECONOMIST: Architecture

Cain is a farmer of some sort, and Abel is a shepherd (remember this part, it will be important later).

FORBES: Dear President Obama: I'm Only My Brother's Keeper If My Brother Is My Sheep