Recapitulation theory
However, not all of Haeckel's evidence or conclusions were this good. Haeckel produced several embryo drawings that often overemphasized similarities between embryos of related species.  These found their ways into many biology textbooks, and into popular knowledge, even though they were wrong. Furthermore, Haeckel used this "evidence" to conclude that white people were evolutionary superior to people of other races. Not only is this a racist view, but we know today that it is not true.