Final answer:
An organism's traits are not determined by averaging the parents' traits in pre-Mendelian genetics. Traits are determined by the combination of genes inherited from parents, and offspring vary in their traits due to the random assortment and recombination of genes.
Step-by-step explanation:
The pre-Mendelian concept that an organism's traits are determined by the blending, or averaging, of the parents' traits is false. This idea, known as the blending theory of inheritance, suggested that the resulting offspring's traits would be a mix of its parents, representing an intermediate state. However, through the work of Gregor Mendel, we now understand that traits are determined by distinct units called genes, which are inherited as separate alleles from each parent. Each characteristic is determined by the specific combination of alleles inherited, and this can result in a variety of genetic combinations and observable traits expressed by the organism, rather than just an intermediate blend.