Would you kindly imagine that in the next few decades we establish our first long term habitat on Mars. The humans that inhabit these semi underground enclosures live almost exclusively inside these with a few surface walks. They started with enclosed capsules but dug into the ground far enough not to be touched by the harsh environment on the surface. The relatively small hydroponic bays expands underground to sustain the slowly growing population. Of course we can't just leave it at that and more vessels arrive through the years building up several different settlements and adding redundancies.
As this is going on technology has advanced just those few inches from today so that a few complex automatons have joined the crews to Mars. There are a dog like and humanoid robots who help those humans build a future on our sister planet. Here on Earth however we've been expanding into more human like robots to show how far we can go and to make them easier to work with. To take care of children and to better anticipate our needs they'll need to understand some basic emotions such telling a joke when you're sad. As they get more and more complicated the lines between biological and mechanical blur. Eventually...
Something wrong happens, something we never suspect but is bound to happen, an android passed from being just a machine into being alive. Can it think, we've programmed it to think on its own so it can cope with different circumstances. Does it have feelings, most likely not how we would think of them but like in the video being scared of dying / not existing sure does count in my book. So how do we classify something that is like us as being equals and not someone we can just turn off without a second though. What is the requirement to be a person, in the easiest way to describe it is that they need a soul.
But I degress that I should probably move on to the part that I started with and that is humans and not our mechanical counterparts. Years and years into the future and we've spread across the galaxy inhabiting worlds left and right. Now lets focus on a special world that is not just seventy some present water but closer to 98%. There just isn't enough land for us to florist so we take to the waters where most of our nutrition comes from the oceans such as seaweeds and fish. Most of our occupations would consists of something under water and we'll start evolving to better suit our new habitat. Fast forward again a few more thousands of years and sub-human aquatic race has emerged on this far away planet. Our bodies have changed so we're faster swimmers and can go deeper, longer, and into colder waters. We've developed a way to siphon oxygen from the water though we're not a 100% underwater species yet on this planet. We might even resemble something like a mermaid.
Now would you kindly imagine that our distant children who stayed on earth and are relatively unchanged by the hand of time and our petty differences set forth and visit this long lost planet of aquatic humans for the first time in an eon or two and two so happen to fall in love. These two species are now distant cousins but still share the same root origins. Would you deny such a relationship when over a hundred thousand years ago the last racism against biological androids was removed as by that point we've been mingling in with them for so long that we've become one species together.
I think I've probably lost my thread awhile ago but still, you've skipped to the end just to read this.