"Solon have a strong sense of what is 'Proper' that includes a lot of arbitrary taboos, and that the thing that separates people from animals is that People can be Proper. Anyone who can't are either sent to a creche until they can, or butchered for their meat. Children need to live in a creche until they learn, usually getting out when they're adult-sized. They're... hmm. It's hard to describe. There's a reason I haven't been suggesting asking them to take you in. They're far less exacting of people who don't live in their territory, and will probably trade with you just fine, though.
"Merfolk have a strong concept of gender. How that's expressed varies from culture to culture. Usually the men and women are separated into groups that have limited interactions with each other, sometimes expected to live in different towns for parts of their lives or exit their dwellings from different entrances on opposite streets, and often doing different jobs.
"It was historically rare in humans to have anything other than slightly different fashions or maybe some minor religious obligations for gender. It's more common now, since most of the fishfolk who created the throwbacks were from the rare places where humans and merfolk intermingled. That, and the focus on repopulation. Many women take jobs that let them carry around unweaned babies. They aren't as bad as merfolk about it.
"Dryads and solon don't have physical sexes. Dryads all seem to be women, but I'm not sure what that means without another gender to contrast it with. The way solon divide themselves between full solon, half-solon and strider is kind of gender-like?