the great depression was a time of economic failure in many countries, so the puchasing of drugs and doctor visits was greatly reduced and made many sicknesses escalate couple this with the fact of poor living condition and its no wonder why sicknesses escalated to the point they did.
It will evolve during trade.
Not to a normal evolution, but Pokemon that can do so can Mega Evolve during battles.
It can only evolve during daytime and with a oval stone.
Riolu evolve by happiness during the day.
Evolve Eevee during the day
During trade it must hold dragon scale to evolve.
Brock's Marshtomp does not evolve during any episodes.
It doesn't evolve at a specific level, but it will evolve when leveled up with high happiness during the day.
It doesn't evolve normally. If you have it hold a Tyranitarite, though, it can Mega Evolve during battle.
Most evolve by getting to a certain level, some evolve on a high level of friendship during the day or at night or just by friendship, some evolve with stones, some at special land marks, some during the day, some at night, and some don't evolve at all.
Sneasel will evolve during the night if holding a Razor Claw.
No