In the former post I reviewed Under a Green Sky by Peter D. Ward. He makes a distressing point or two about living on a tropical planet.
The human species evolved primarily during ice ages, particularly the 100,000 years since "anatomically modern" humans arose. The tropics (the 30% of Earth's surface between 23°S and 23°N) were more temperate than now, perhaps by 8-10°C (14-18°F). Dr. Ward writes
"We who live in the more comfortable climes seem to think that just because the human tribes who lave long inhabited the equatorial zone have evolved through many generations living in constant heat, night and day, that somehow these people no longer feel the heat and humidity, that unlike us, they are not made uncomfortable by the horrible climate. Not so."Maybe we've all read or heard of people in the tropics who seem able to work in the heat without sweating much. It is never stated that they have a secret. Nearly everyone who lives in the tropics without air conditioning uses one or another of the legal drugs so abundantly supplied in tropical plants.
Remember, most plants are trying to avoid being eaten by herbivores and omnivores. Woodiness helps; even many leaves (such as elm—ever chewed one?) are woody and unpalatable. Grasses and sedges incorporate silica crystals in their tissues to make them harder to chew. But most plants use chemical defenses, hence their bitter taste. The taste isn't just a sensory deterrent, it usually indicates the plant is poisonous.
Some plant poisons that kill or weaken insects and other small animals don't harm people nearly as easily. The common substance Caffeine is an insecticide, and deters some small mammals, but office workers worldwide consume a half gram or more daily "just to keep going." By chewing coffee beans and camellia leaves (tea leaves), people for centuries used Caffeine as a stimulant and mild analgesic...it really does help you cope with heat.
Caffeine is just about the only "heat helper" that doesn't hinder mental acuity. Around the world people use Kava (Polynesia), Betel (Indochina), Marijuana (almost anywhere, often used with one of the others), Khat (India to East Africa & Turkey), and Coca plus Cacao and Coffee (South America).
With or without drugs that can numb the mind, tropical heat is so enervating that one cannot sustain critical thinking. It is well known that few great mental achievements arose in the tropics. This is not because the people living there are less smart, but that the climate makes them work extra hard to have any thoughts at all.
I've worked with people who were born in hot places, now living in temperate America. They are formidably intelligent, whether from Uganda, Colombia, or Vietnam. But now we're coming to a subject covered in more detail by another book I'll review soon. Just a point from issues that overlap that book and this one:
Drop a typical urban or suburban Westerner into the Congo, New Guinea, or the Amazon, with an overnight bag and a knife. Set up a betting pool on when he or she will die. It'll be a matter of days. Now drop a typical native of the Congo, New Guinea, or the Amazon into New York City, London, or Paris, with an overnight bag and a knife. His or her grandchildren are likely to own the building your grandchildren work in. So who is smarter?