There were many classes even among the humanity, and the manner in which these distributed themselves over the Earth-chain needs some explanation. It is the general rule that those who have attained the highest possible in any chain on any globe, in any root-race, are not born into the beginning of the next chain, globe or race, respectively. The earlier stages are always for the backward entities, and only when they have already passed through a good deal of evolution and are beginning to approach the level of those others who had done better, do the latter descend into incarnation and join them once more. That is to say, almost the earlier half of any period of evolution, whether it be a race, a globe or a chain, seems to be devoted to bringing the backward people up to nearly the level of those who have got on better; then these latter also (who, in the meantime, have been resting in great enjoyment in the mental world) descend into incarnation along with the others, and they press on together until the end of the period. Thus the first of the egos from the Moon who entered the Earth-chain were by no means the most advanced. Indeed they may be described as the least advanced of those who had succeeded in attaining humanity--the animal-men. Coming as they did into a chain of new globes, freshly aggregated, they had to establish the forms in all the different kingdoms of Nature. This needs to be done at the beginning of the first round in a new chain, but never after that; for though the life-wave is centred only upon one of the seven globes of a chain at any given time, yet life has not entirely departed from the other globes. At the present moment, for example, the life-wave of our chain is centred on this Earth, but on the other two physical globes of our chain, Mars and Mercury, life still exists. There is still a population, human, animal and vegetable, and consequently when the life-wave goes round again to either of those planets there will be no necessity for the creation of new forms. The old types are already there, and all that will happen will be a sudden marvellous fecundity, so that the various kingdoms will quickly increase and multiply, and make a rapidly increasing population instead of a stationary one.