Permanent changes to entire zerg strainsKerrigan was once merely human. Today, she is the vanguard of zerg adaptation, and her altered DNA promises new genetic futures for the hungry swarm. As you progress through the story of Heart of the Swarm, you’ll have the option to drop down to the surface of isolated planets on evolution missions – the hunt for rarefied genetic material to assimilate.
Playing evolution missions will give you an opportunity to devour the creatures that provide the swarm with its evolutionary punch, then experiment with your newborn zerg variants. You’ll be able to learn about the powers of each new strain, and send them on a mission to test out their capabilities and evaluate them for induction into your swarm.
Experimenting with these units is important, because each evolution mission will present you with a choice: in which direction will you evolve the swarm? Will you make zerglings birth more of their kind from a single egg, or grow wings to carry them over cliffs? You can only choose once for each unit…and your choice is permanent.