Blending inheritance is a theory of heredity that was popular during the 19th Century, until it became replaced by Mendelian theory (see Mendel's first law and Mendel's second law).
Although Mendel's laws come with their own issues of necessary addenda and revisions, the critical flaw with blending inheritance is that two mating organisms can produce an outlier organism for a given trait. Perhaps the simplest example of this phenomenon is that of two short parents who have a very tall child.
