PEPCK-Cmus - Superhiiret.

These genetically engineered mice also eat 60 percent more than controls, but remain fitter, trimmer and live and breed longer than wild mice in a control group. Some female PEPCK-Cmus mice have had offspring at 2.5 years of age, an amazing feat considering most mice do not reproduce after they are one year old. According to Hanson, the key to this remarkable alteration in energy metabolism is the over-expression of the gene for the enzyme phosphoenolypyruvate carboxykinases (PEPCK-C).

Ask A Scienceblogger - Which parts of the human body could you design better?

The third thing I'd fix would be human aggression. There are socially maladaptive behaviors that were evolutionarily useful but now, not so much. Aggression, jealousy, selfishness. Mostly a problem of men, we are too violent and prone to rage.

Let us understand, once and for all, that the ethical progress of society depends, not on imitating the cosmic process, still less in running away from it, but in combating it.
- T. H. Huxley