Variations on a theme of DejaMorgana
I had been thinking about the Crystal World structure DejaMorgana laid out for his 'Crystal Sky' shared world. The idea was for two planets obriting the sun in a binary system, and with tidal effects having slowed down the planetary rotation to the point where there would be three or four days a year.
Thinking about what such a world would be like, the first thing that struck me was that days would be more like seasons. A twenty degree drop between day and night is normal here on Earth. Any planet with a six week day followed by a six week night would endure some rather significant temperature changes. The climate would be interesting. Night might equate to winter.
So when i think of life evolving on such a world, it's going two ways. Either a species is extraordinarily tolerant of temperature, or it's really mobile.
One way to gain temperature tolerance is hibernation. Plants would have to mature very quickly, so during the day you'd eat like a pig, find a cave and then sleep off the night. A sentient species might build a better cave. Or, animals would have to develop extraordinary temperature regulation abilities.
Feathers have the best insulation to weight ratio. Hair though, is easier to grow, and better in water. Plus fur can be shed. However, in high heat fur may make sweating impractical. Dogs shed heat through their tongues, and that's not a very big heat sink. Bare skin is good in heat, bad in winter, and it seems doubtful you gould get throug the australopithicus stage of evolution without figuring out the virtues of the fur coat.
So, if we want a humanoid mammal, I bet they hibernate, and build a den to gain the extra insulation. A shared den becomes the beginnings of a town, with a summer above surface component and catacombs for hibernating at night.
An alternative strategy would be speed, to try and outrace the darkness. I can see only three ways to accomplish this. Birds migrate by flying, and some birds are large enough to lift a reasonable braincase. But I wonder if such an avian would be unbalanced by the mass of a large brain in the head. So maybe you move the brain to the body, and have a couple of flat, brainless heads like a puppeteer.
Another strategy if the land were wide enough, would be the centaur model, where the animal would be built something like a horse and thus could gallop ahead of the darkness. Or something wheeled like the g'kek from David Brins Uplift Universe. But I have my doubts there as well, Rivers, ice flows and geothermal effects produce some really bad terrain. Horses climb very well on some types of terrain, but really badly in others. And climbing is slow. You don;'t want to climb if you're trying to feed yourself and outrace a signficant weather change. Plus, what is Centaur Seabiscuit to drink while racing across the planetary plains?
But an aquatic species might do well. Dolphins can go very quickly when they have a mind to. Oceans stabilize temperature. The seasons would bring temperature difference, but it would be moderated in the water. They could go out to sea during the tides. And supporting a very large brain is not at all an issue.
So, from my perspective, the most likely civilization is a land-based group of sleepers and an aquatic civilization, that may not like each other.
As a land animal with a limited amphibious capability, i naturally identify more strongly with the hibernators. Especially when my alarm clock goes off. The need to quickly gather and then hibernate would might keep them in the hunter-gatherer stage longer than humans did, simply because the benefits of agriculture might be less obvious. You wake up really hungry from your rest, and you might have to spend so much time just gathering food that you'd never think to plant anything. And the crops you chose would have to mature quickly in order for sufficient supples to be gathered. So i guess that farming would be a relatively late vocation.
However, fishing does fall under hunting AND gathering. A sentient species might innovate canoes, spears and other tools to make them more efficient fishermen. A dugout canoe might be prepared and stored over the hibernation. if the fishermen were efficient, they might feed the tribe while others grew grain
Therefore, I'm guessing they develop bath aquatic technologies and weapons before the plow. If you develop aquatic technology quickly enough you gain the ability to migrate rather than hibernate. Ships carry weight very well, which might allow you to take crops with you. Particularly when you remember that wind is created when high pressure air rushes to fill a pressure area. I'd bet that the twilight and dawn would be announced by a jump in windspeed. Which means that sail might be an efficient way of migrating.
On the other hand, the strong tidal effects produced by having a very, very large companion would make sailing, difficult. Deep water anchorages would be prized, and in such places canoeists to ferry the sailors would make a good buck. Deep water anchorages surrounded by arable land would be ideal. And forests for fuel and building materials. Although stone might make for better longevity. I would also bet almost all ships would have some rowing capacity like in a galley. Strong tides might force seamen to move a ship quickly against, or without, wind.
One things for sure, they'd grow up eating a lot of fish. And I expect fish on an alien planet to look a lot like the Terran varieties, as waterdynamics remain the same everywhere. Charlie may not be a tuna, but he'll look like one.
So, imagine a migratory group of tribes, moving from one seasonal city to another. Perhaps one tribe might try to grab and occupy the most desirable towns. Would you garrison desirable towns, so there would be a defense? Or move some people before the harvest is complete to stay ahead of the town robbers. What would a tribe do, arriving expecting to eat the supplies they stored during last summer, only to find robbers there ahead of them. Predation would be well rewarded.
Also, if the hibernators--- I'm picturing small bears here but for story purposes they could look like people-- eat a lot of fish they'd compete with the aquarians for fish. Natural competition for resources would lead to inter-species conflict as populations grew. Would all ships need marines to protect them from the aquatic sentients? Would they even recognize the other species as sentient? I see lots of sea monster tales here. And a world with a lot of conflict, one that would greatly benefit from a central government to keep the natural conflicts to a dull roar.
Right now i'm really wishing that i had the world building chops of a Hal Clement. This planetary geology in this very different system carry in themselves the seeds of many interesting tales.
Lately it occurs to me that some species would evolve to fill the nightime mix. After all bats use a form of sonar to navigate after dark, and it isn't inconcievable that a species might 'see' in the infrared. One interesting possibilty is for a small heat-seeking parasite that infects hibernators. It could be unintelligent, but either form a symbiosis, or consume them, and lead to a rabies sort of madness. Whole tribes might be wiped out, leaving abandoned cities. Said cities might prove very dangerous, because who could be sure if the predators had left.
At the same time, any species that evolved 'chasing the sun' or hibernating might not have very good night vision. No reason to evolve it. Whereas if humans were a transplant, they might see fairly well by local standards. That would make us particularly effective as police, soldiers and as theives.
A question I would like answered concerns the wind. on earth we have prevailing winds at certain lattitudes, and they very by location with northeast winds and southwest being the most common. I am not certain Earth's 24 hour rotation plays into this, presumably it does something that would be left out in a 'long day' world.
Now, if you are chasing the daylight, it would be better to have the wind at your back. It is possible to sail into the wind. Sailors call this beating into the wind, and while it's fun, it's also interesting and much more time consuming that sailing with the wind as beating requres approaching the wind at no more than a 45 degree angle. Unless you're driving a 12 meter yacht in the America's Cup.
On earth, the direction of prevailing winds varies by latitude and the doldrums, or low wind areas are found at the boundaries of prevailing winds. If this pattern repeats itself certain latitudes would enjoy distinct advanatages at 'dawnchasing' Depending on the length of the night, some may prefer to try and sail through it and simply put up with a shorter cold period. This creates a an interesting picture of some clans or tribes sailing against the wind, others with it depending on latitude, while some go the other way and trhough the night. Also some might get trapped in the doldrums duirng the night, which raises the specter of some lost tribes, abandoned or dead ships drifting free in the sea lanes as their crews either starved or froze to death.
This also suggests that geographic choke points might prove very profitable during a migration. Hibernators might occupy and maintain certain sea level canals-- like Suez-- for a small 'contribution' Robber barons might do well.