Notice in the picture how the one tray of tomato seedlings looks way further along and happier than the rest.
The only difference was that the plants that are grew much faster were from seeds that were saved on site by me. The rest were purchased (but very high quality.) Same soil mix, same type containers, same watering, equal lighting — the exact same conditions.
Other than consciousness affects, the source of the seeds is the only theory I have as to how there could be such a marked difference in the growth. I would assume because they are already that much more adapted to our local conditions. Yay seed saving!