Avadhoot

The practise of strict brahmacharya will promote one to the higher planetary systems like Tapaloka, etc. If everyone followed such tapasya it would be very nice for all, as family attachment naturally leads to rebirth in this world. As far as the population of humans we know that from the animal species automatically souls enter the human form, in the mode of goodness from cows, in the mode of passion from tigers,lions,etc. and in the mode of darkness from monkeys,apes, etc. It has also been written that those who have spent their good karma on higher planetary systems will again come down to Earth as is stated in the Bhagavad-gita "kshine punya martya lokam vishantee". As it is commonly understood, nature {God} abhors a vacuum.