Half of the project was preserving the knowledge base of the Alterra. This meant every piece of history, science, technology, language, geography, society, etc. Compiling the database took a considerable amount of time, but the harder task was the physical transformation.
The Repository not only downloaded information into the user's mind, it altered their genetics into an Alterran template. The Seed Species would become Alterra in both mind and body, with the later transformation taking up to 10 years until final completion of the 'maturation' phase.
In order for the Repositories of Knowledge to be able to create new Alterra in the distant future, they had to have a sufficiently advanced Seed Species available to transform. The level of development required would also be succeptible to the plague, thus a very primitive version was created and spread through seven different galaxies in order to maximize the chances of at least one of the Seed Species surviving and advancing to the desired point, at which one of them could use the Repository of Knowledge and begin rebuilding the Alterran civilization.
Present day Humans are the eventual evolution of the Seed Species in the Avalona galaxy.
Laboratory growth of sufficient numbers of seed species was unviable given the limited amount of time the Alterra had to complete the Legacy Project and the number of personnel they continued to lose through attrition, so a 'mass-deployment' technology was developed that would seed individual worlds by means of a matter-reorganizing energy wave deployed through the stargate. This device was located on, ironically, the same world where the Alterra placed their first colony in Avalona...Dakara.
It was through this device that the Alterra seeded six galaxies with protoforms made from disassembling existing non-living organic matter on the targetted world and reorganizing it into clusters of 'pods' that acted as quick grow incubation chambers. The genetic material required for these pods was distributed to the targetted planet before the energy matrix would arrive.
The matrix would persist for several hours, with additional energy passing directly through the stargate that was needed to accomplish the reorganization of matter, whereas the initial destruction required only the first wave to accomplish.
After the targeted material was disassembled, the energy matrix would then redeploy and assemble the required raw material for the 'seeds' already present. After a few days of growth, the fully mature Seed Species would emerge from their cocoons to begin their new lives in the 'wild.'
The Alterra were not cruel, however. On every world they seeded, they also left basic shelters and food dispensers that would last the better part of a decade...tappering down production towards the end to encourage the Seed Species to look for other sources of nourishment. A few of the Alterra even tried to help some of the newly seeded planets get a foothold by providing instruction and guidance...but the Seed Species was so primitive that communication on any functional level wasn't possible. They did manage to leave a few telepathic instructions inbedded in their memories to guide them in their acclimatization, but in the end the Alterra simply let them be, saddened that their great civilization had been reduced to this level of barbarism.
The Alterra's allies agreed to watch over the new Seed Species as best they could, with the Asgard and the Furlings taking on a more protective roll, while the Nox kept an 'open door' policy for any of the Alterra's 'children' who stumbled onto them through the gate network.
The Asgard's war with the Goa'uld was a direct consequence of their exploiting the Alterran's seed species as both hosts and slave labor. The Protected Planets Treaty was the Asgard's attempt to preserve and teach some of Avalona's remaining Seed Species in lieu of ridding them all of the Goa'uld...something that was logistically impossible at the time.