The Human Race has remained much the same for over 3,000 years, with little noticeable change in their outward appearances or inward structures. Cultures and fashions may alter dramatically, but human physiology has remained the same.
And so in the 26th century, humans who are born on Earth look little different from how they did in the 21st. Changes in lifestyle have meant that Earth humans are slightly taller, better educated and healthier. There is little true obesity amongst the population, laws were passed in the mid-21st century regarding food composition, and a social shift in regards to eating stamped out this problem.
Humans born on colony worlds can be different, however. Differences in gravity can produce either taller or shorter humans (with lower gravity, the inhabitants tend to be taller and vice versa) and also the physical robustness of the body. Humans born on higher gravity worlds tend to be stronger, as their bones are more developed, whilst low gravity humans are more fragile than an average, Earth born.
Genetic deformities and hereditary diseases have been all but removed from the population due to complex screening procedures before birth. Most diseases from the 21st century, including cancer and AIDS have been cured by the dawn of the 26th century.
Cloning is possible, but is still an extremely contentious social issue. There are a number of illegally produced human clones living on Earth and the Terran colonies.