It's not a given. Some people seem to "learn" from being shown where the firewood is how to gather it and renew the fire. Some don't. That's why I teach 3 or 4 people to do it, because I've seen that one or two of them will gather firewood on their own. I've had fires with 3 hours left that had 14 hours left next time I checked, so someone is feeding the fires
You do need an adept builder to make the dam, but you can do that after you get the building tech raised, if you like. Point is to put the majority of your people on tech, build that dam and start farming ASAP, then shepherd the farmers so they actually harvest crops and don't go kiting off after the coconuts. You really do have to babysit this game, it doesn't run as well on auto-pilot as the last one does.