why over evolution did we lose our tails?

Question: why over evolution did we lose our tails?
- Keywords:
  evolution,
  lose,
  tail
Asked by TomBlyth2004 to Deborah, Euan, Maheen, Rob, Stu on 17 Jun 2016.
- Maheen Siddiqui answered on 17 Jun 2016:
  
  There is a rule of evolution that if an organ is not used for a long time, it disappears. So the tail was probably less and less useful over the years and evolutionary pressures caused it us to lose it.

Question: why over evolution did we lose our tails?