<ref name="Kusnezov_1967">{{cite journal |first1=N. |last1=Kusnezov |year=1967 |title=La ley de la desigualdad del desarrollo |url=https://antcat.org/documents/1887/11044.pdf |journal=Acta Zoologica Lilloana |publisher= |volume=21 |issue= |pages=123–251 |doi= }}</ref>