The scrotum is designed to keep the Testicles 'cooler' and in Equatorial regions, men didn't use warm underwear and the scrotums hung lower - unlike in Polar climates where warm pants were the go.
In Polar climates, (especially underwater) creatures grow bigger, breed slower, but live longer.
In equatorial seas and lands, creatures are smaller, breed faster, but live shorter lifespans.
Ironically, a thing called 'Religion' also manipulates the breeding pattern in humans. Yep - its all in the mind
Mohommedism, Catholicism, etc - can provide a 'mass production' of breeders.
While Judaism and Protestantism - provides slower breeding but a wealthier mass.
USA: Politics - slow breeders, fast earners.
Art - fast breeders, slow earners.
The Albury Sperm Clinic is in dire need of Sperm Donations.
In the last 5 years - all that they have received is sperm from Indians, Pakis & Sudanese... and 'Gay' white males.