Mastering biological processes so that we can ensure that there is enough food for everyone (of a reasonable variety)[1] and that maybe the plants can do well and clean up our environment and make it nicer to live in?[2] Maybe to achieve long enough human lifespans that we can think of interstellar travel?[3]

1 - Hal Clements _Space Lash_, short story "Raindrop"

2 - L.E. Modesitt, Jr's The Forever Hero trilogy (as well as the "The Mechanic" from Space Lash)

3 - Poul Anderson's _The Boat of a Million Years_