seems like the saiyan race were like the pinnacle of evolution. their bodies are capable of rapid adaptation to fast changing environments. They are able to use energy conversion in such a way that they can convert a lot of matter (lots of food) into very strong body. this process can constantly react to the environment through what must be super intelligent processes within the body itself. it seems to be able to adapt to increasing adversity via the channelling of ki. whereas most creatures have a limit to the amount of ki they can channel, the saiyan seem able to reconfigure the methods of channelling and making it more efficient. through training, the body can be told to make it more efficient, to open more pathways to channel more energy. it seems they are connected to a source of energy even beyond the afterlife. I was surprised that the dragonball series did not explore beyond the afterlife and introduce even deeper dimensions that could hold the origin of ki energy.