It had all started with an accident. The generation ship had not intended to land on this planet. While the environment was livable to normal humans, the planet was small and resource poor. It was mostly swampland, with too little solid ground to support a colonization effort. But the ship had been travelling for thousands of years, far longer than had originally been planned, and no suitable planets had been discovered. A malfunction forced an emergency landing on the planet, the only remotely habitable planet in within reach. Unfortunately, the ship could not be saved and the colonists were forced to live on their new home.
There were few resources at their disposal. If normal humans would find the planet too difficult to live on, then they would use their skills at genetic engineering to modify themselves to make themselves amenable to the planet. They made themselves part human and part frog. Every colonist underwent the change. No one was exempt. Their legs were lengthened into a frog's powerful hopping legs, while their arms became the webbed front legs of a frog. Their 'hands' retained limited ability to grasp objects, but the humans of this new planet would never have the dexterity of their ancestors. Mobility was more important in this environment. They gained the frog's tongue, which they used to catch insects and other small native animals, and their digestive systems were altered to be able to digest anything, even things that would have killed them previously.
Even their reproduction was altered. While their human half was still 'male' or 'female,' their frog halves would be fully functional hermaphrodites. Both genders could now become both mothers and fathers. This would ensure that there would always be a potential mate, regardless of composition of any group. Men would prefer to have sex as men, and women as women, but would enjoy sex as either gender. They laid eggs like a frog, with tadpoles with human heads hatching out, who, like frog tadpoles, would eventually develop into their adult forms, shedding their tails and growing limbs. Until then, the parent who had laid the eggs would instinctively protect their offspring as they developed. Finally, while the orignial colonists were the same size as other humans, their descendants would be engineered to be smaller, to have fewer material needs and to avoid overtaxing the environment.
The colonists gradually adapted to their new forms and planet, explored their new world, laid their eggs, raised their young and made new lives. Time passed.
