(AP) - Traces of blood and fragments of muscle, tendon, skin and hair found on 2,000-year-old stone knives have given researchers the first conclusive evidence that the obsidian blades were used for human sacrifice so long ...

Other Sciences - Archaeology & Fossils

May 03, 2012 4.4 / 5 (7) 3 |

(PhysOrg.com) -- The origins of altruism, the willingness to make personal sacrifices for the benefit of others often unknown to us, has perplexed evolutionary social scientists and biologists for years.

Other Sciences - Social Sciences

Oct 23, 2009 3.9 / 5 (9) 8