?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.au=Sigmund%2C+K.&rft.aulast=Sigmund&rft.aufirst=K.&rft.date=1996&rft.isbn=3-211-82936-9&rft.title=The+natural+history+of+mutual+aid&rft.btitle=Wissenschaft+als+Kultur&rft.genre=bookitem