A theoretical perfect human would never have a disease or illness and have perfect control of their thoughts, emotions, and actions. Humans would not be born missing limbs or with extras, or with things like missing or extra chromosomes. Basically, the DNA (which would be undamaged and free of genetic anomalies) in humans would be followed perfectly by the human body.

I would even say the theoretical “perfect human” would never age beyond maturity or die of old age. Scientific observation shows the human body has built-in functions to account for this, as all cells in your skin are replaced every 7 years for example, but for some unexplained reason, things start to go wrong which is part of what we call aging. Science still has not exactly determined the cause. One theory is cumulative cellular or DNA damage caused by various factors over time like stress or radiation and such. Another theory is that DNA has a pre-programmed life-span. Neither of these have any definitive scientific proof or evidence at the present time, though theories often fluctuate as more evidence is uncovered, so these may change in the future.

As to the appearance of this perfect human body, it would very much look like young healthy humans we see today. There is great variety contained in the human genome, and none of these varieties would be considered any better or worse than others. Skin tones, eye and hair color, height and weight, even intelligence levels, are all factors that can vary greatly in human DNA.