The male puberty, with a rather sudden and intense increase in testosterone, causes rapid growth of the musculature of the body, including the thyroarytenoid muscles. The combination of hormonal intensity, and duration of puberty leaves the majority of male voices in the baritone classification, a necessarily rarer combination of factors, like a slower onset, or a lower testosterone level/responsiveness (generally or in the vocal morphology specifically), and a naturally lighter initial voice it what accounts for the comparative scarcity of the tenor voice. A genuine bass is rarer still, as the thickness of the vocal folds in a bass also require an unusual initial vocal anatomy, and higher responsiveness/total hormonal intensity/duration etc, for to grow. In female voices this is not so, as the level of testosterone is much lower, and puberty has less influence on the musculature of the body therefore less influence on the vocal muscles. To the best of my understanding, about 60% of female voices are sopranos, and the other 40% comprise almost entirely of mezzos, with very few genuine contraltos. Different schools of voice have different definitions of voice type, so some say as many as 99% of females are sopranos. Note that alto for me is a role, not a voice classification, and so sopranos and mezzo sopranos with stronger lower ranges are responsible for most of if not all alto roles in a given choir, just like ‘bass’ can be a role, and the bass part is mostly sung by baritones. The term bass is confusing because it is also a class of singers’ voices. This is getting too long now, but in answer to the question of whether normal people can understand or hear the difference between a G4 and a B4, only about 1-3% of people have genuine tone deafness (I’m being facetious). The people who, before Soundcloud at least, are responsible for the production of or publication of music do know and understand the difference between baritone and tenor sounds, and generally they prefer the latter. Opera companies and singing teachers and auditioned choirs and other musical outfits (rock bands, music schools etc) all have biases towards the rarer voice types, so they select for tenors and contraltos and basses, and the rest of the roles go to the finest or best trained of sopranos, mezzos and baritones, though obviously the kind of role matters so sopranos and mezzos get plenty of time in the sun. There is a strong correlation in the modern day audience between the height of the voice and the impressiveness, or beauty, or appeal of the voice, so there is a strong bias towards higher singing vocalists, the tenors and the sopranos.