It just seems like it would be a really cool thing to have gills and be able to populate the oceans in the same way we populate the land. We could have houses and shops and vehicles, andgo on walks/swims and just kind of live underwater.
Start a whole new second species of human here on earth maybe, Who knows?
If you like this, this goes under the moniker ‘evo/dev’ - evolution of the ‘development’ of the organism. A lot of genes don’t code for proteins that ‘do’ something in the body, like haemoglobin or fingernails - they code proteins that tell the body how to develop from a single cell. Many are active for a short window in development. Some are active in a single location, like at the thumb end of the limb bud, and tell the cells where to become a finger, thumb or palm bone. Some work across vastly different animal classes - the ‘build an eye here’ gene works in humans and flies and everything in-between.