Carried to its logical conclusion in a consumer society, it also allows people to customise their appearance through superficial cosmetic changes, alter their sex, or even to fuse their body with another person's.
Multiple colonies have been established on asteroids and cometary debris throughout the Solar System, in which isolated groups implement quixotic and highly questionable form changes to bring about their own personal utopias.
One of the most extreme forms is reminiscent of a kangaroo with highly adapted circulatory and respiratory systems, allowing survival on the surface of Mars.
She is a recent addition to the force, arriving just three years after the retirement of the legendary Bey Wolf, one of the greatest form change experts alive.
She is assigned to a strange case by her superior Denzel Morone: several instances in which the Humanity Test has been successfully applied, but the "infants," if they could be called that, are feral monsters.
Knowing that there is no way the specimens could have (or should have) passed the test, and also aware of her own limitations and inexperience, Sondra seeks advice from Bey Wolf, her distant relative.
Sondra Wolf Dearborn arrives unannounced and uninvited, and he berates her before sending her off, telling her to visit the distant colony and inspect the Humanity Test equipment herself for possible flaws.
He is ready to put her out of his mind when he receives another unwelcome visit, this time from Trudy Melford, president of BEC: Biological Equipment Corporation, the manufacturer of all Form Change tanks for the last 150 years.
Trudy Melford is one of the richest and most powerful people alive, and a personal visit to a remote island is evidence of great urgency and need on her part.
Bey Wolf, annoyed by Trudy's interruption, is nonetheless intrigued by her offer of a position at BEC to work on revolutionary new forms.
Sondra enlists the help of Bey Wolf's friend Aybee, a physicist and administrative genius, to further investigate the malfunctions and charter a flight to the Fugate colony, site of the first Humanity Test failure.
This experience heightens his suspicions; the BEC engineers are ingenious, what problem could possibly be so important and so intractable that it warrants Trudy Melford's personal recruitment efforts towards him?
Bey Wolf is beginning to realise that a very complex mystery is unfolding around him, and he has a hunch that the Humanity Test false positives are involved.
For the past hundred years they have been shuttling comets to Mars and smashing them into the equator, gradually increasing the humidity and thickening the atmosphere.
He persuades Trudy to send him back to his home on Wolf Island, where he programs a dangerously rapid regeneration procedure into his customised Form Change Tanks; in just under a week, he'll be out and walking again.
Unable to relinquish her son to the organ banks, Trudy instituted a massive coverup and faked his death during a boating accident.
Trudy's ultimate goal was to undermine the legitimacy of the Humanity Test itself, by engineering defects into BEC equipment so that obvious non-humans would occasionally score a false positive.
Parks stated that Sheffield "manages to include a few interestingly oddball characters along the way" and is "at his very best when depicting scientists happily working within their chosen specialties".