The half lives are a cross breed between humans from Earth and non-human races from the other planets.
Half life expectancy decreases exponentially with time
The name comes from the term Half-life, abbreviated t½, which is the scientific term used to denote the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms (radioactive decay.) it may apply to any quantity which follows a set-rate decay. One of the key characteristics of half lives is that they age at a rate which is 50% faster than humans. In 3017 most half lives have a life expectancy of fifty years, while their human counterparts could easily live to be a hundred.
The Lion Man: Half human half lion
The first recorded half lives were born in 2100, by which time the distances between planets could be covered in weeks instead of years Earth time. Technological advancement and the discovery of wormholes between planets further shortened travel times so that by 2900, such space could be covered in days.