Humans still aged, but most people got STEM shots to rejuvenate cellular functions to mid-twenties biological age.
Humans at the time of To Sleep in a Sea of Stars could be enhanced in a number of ways. First of all were gene-hacks. These ranged from a set of fairly standard, widely-accepted alterations that addressed a number of common issues in the human genome to massive bodily modifications—many of which were so dangerous as to be illegal. The settlers of Shin-Zar were notable for having engaged in population-wide genetic enhancement with the aim of adapting to a high-gravity lifestyle.
Most military personnel received some level of genetic modification, with the amount being proportional to the demands of their position. Special forces, for example, received some truly outlandish alterations. Myostatin reduction was one such change. Another, more common one, was replacement of the iris and pupil of the eye, to give the soldier a more cat-like appearance, much like the eyes of the tigermaul on Eidolon. Practically, this helped with target acquisition and low light combat.
STEM shots, which could extend human lifespans almost indefinitely, were another possible alteration.
In addition to gene-hacking, it was not uncommon for people to modify their bodies with technology, some quite extensively. The most common additions were neural implants, which allowed people direct mental access to a computer system via visual overlays and induced audio-tactile sensory information.
The rarest and most extreme modifications involved total body replacements. If a person’s body was damaged beyond repair but their brain was intact, it could be transplanted into a vat-grown body. Also, see Construct and Ship Mind below.
These artificial bodies were more machine than biological. Like vat-grown bodies, they were used to save lives in extreme situation. A construct body housed the original brain and provided enhanced abilities, but there was some loss—or alteration—of physical sensation. Some people after spending time in this form chose to become ship minds.
Ship minds were the result of a confluence of factors: human desire to push their intellect to the limit, the failure to develop true artificial intelligence, the increasing size of spaceships, and the destructive potential of any space-faring vessel. Having a single person, a single mind, to oversee the many operations of a ship was appealing. However, no unaugmented brain was capable of handling the amount of sensory information a full-sized spaceship produced. The larger the vessel, the larger the brain needed.
Brains from volunteers, often constructs, were removed from their bodies and placed in a neural sarcophagus, a cradle of sorts. It was surrounded by a growth matrix and bathed with nutrients to induce tissue expansion and synaptic formation.
Ship minds were some of the most brilliant individuals humanity produced. Also, in cases, some of the most disturbed. The growth process was difficult, and severe psychiatric side effects sometimes occurred.
Ship minds—both on and off ships—were responsible for directing far more of the daily affairs of humans than any but the most paranoid suspected. But while their means and methods were sometimes opaque, their desires were no different than those of any other living creature: to live long and prosper.