1. Research Life Engineering (available after gene tailoring)
2. Build Evolution Labs on any planet to get Life Breeders
3. Use the decision on any planet within your empire to create a species
3a. If used on a colonized planet the species will be part of your empire
3b. If used on a non-colonized planet the species will become stone age primitives


You get a prompt to choose which biological type the species will have. It might take a bit (in-game) time to create the species, but you will get an event as soon as it is done.