Why are the lungs made up of these progressively smaller tubes and then

millions of tiny alveoli rather than each

lung just being a large empty sack?

because in a giant air sack, there would be no way for the capillaries to exchange gasses, and we would suffocate

Explanation:

the alveoli can only exchange one molecule at a time, they go from our lungs to our bloodstream and not mixing them up.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

emerging idea only occurs as a raw idea that could appear out of nowhere. meanwhile, to reach scientific consensus , that idea must be structured and tested over and over again through various experiments. the scientific consensus transforms the raw idea into idea that is more reliable through the process of scientific elimination.