Though many of our anscestors have contributed positively to humanity we have one that will forever live in infamy, though keep in mind that there is some debate over whether or not Sawney ever actually existed (http://www.bbc.co.uk/scotland/history/sawney_bean.shtml). Sawney Bean was the head of an incestuous cannibalistic family that killed over 1,000 people. He and his family of 45 lived in a coastal cave for 25 years that was 200 yards deep and piled high with human bones.
They were able to hide out for so long because the entrance was blocked by high tides, which was how they were able to stay hidden for so long. It took the help of the Scottish king and a battalion of soldiers to bring them to justice. http://en.wikipedia.org/wiki/Sawney_Bean