I believe that Kerbals spontaneously pop into existence. No reproductive cycle, they just sort of appear there. Any that appear with a mustache and glasses (You cannot appear with one and not the other) are instantly hailed as geniuses and promoted to scientific positions in KSP without any other qualifications. Similarly, Kerbals have a natural defense mechanism where when they sustain potentially fatal injuries, they disappear in a puff of smoke and are teleported to the nearest emergency medical facilities, complete with comically-ineffective full body casts, neck braces, IV bags and wheelchairs. Immediately after their several-day recovery they are launched back into space.
