Defective humans

3-legged baby. Is that a defect? Maybe we, the 2-legged beast, are the defectives babies. Maybe, just maybe, 98% of humans are born with defects and those 3-legged (2%) babies are normal.

I wondered, if defects in humans are defined as anything that is not normal, i.e. different from the majority. Or can our biologist actually identify that we are suppose to have 2-legs only and the third one has no function, only hindrance.