Long ago, a tribe of apes formed an agreement with the tribe of grass. The arrangement was a simple exchange. The grass would give up most of their bodies to feed the apes, who desired a stable source of food. In return, the apes would become their caretakers and champions, waging endless war on the grasses' behalf: against weather, disease, fire, poor soil, natural disaster, other plants, other animals--even amongst themselves. They would apply their ability to analyze and plan, unique in all the tribes, to ensure that grass would grow in every corner of the world, until the end of time.
Ten thousand years have since passed, and this ancient alliance is the cornerstone of the modern world. That tribe of apes now call themselves humans. They number in the billions. They live everywhere on Earth--on land, on sea, and even a few who live above the sky. The tribe of grass has similarly flourished. The beneficiary of human care and terraforming, they grow everywhere the humans live in great quantity. Their names are honored in human language, often synonymous with food and livelihood.
This agreement is not the first the humans have formed, but it is by far the most successful. The greatest pact remains relevant even today--grass still provides well over half of humanity's food. It has shaped and sustained their society. The future of the human and grass tribes are and will be forever intertwined. As the humans turn their attention to lands beyond Earth, grass too will go into the beyond with them. With time and more than a little luck, both human and grass appear set to survive the eventual death of their ancestral home.