Dutch microscopist Anton van Leeuwenhoek discovered animalcules in the sperm of humans and other animals. Some scientists speculated they saw a little man inside each sperm. These scientists formed a school of thought known as the spermists. They contended the only contributions of the female to the next generation were the womb in which the homunculus grew, and prenatal influences of the womb. An opposing school of thought, the ovists, believed that the future human was in the egg, and that sperm merely stimulated the growth of the egg. Ovists thought women carried eggs containing boy and girl children, and that the gender of the offspring was determined well before conception.

Pangenesis was an idea that males and females formed pangenes in every organ. These pangenes subsequently moved through their blood to the genitals and then to the children. The concept originated with the ancient Greeks and influenced biology until little over 100 years ago. The terms blood relative, full blooded, and royal blood are relicts of pangenesis.

Blending theories of inheritance supplanted the spermists and ovists during the 19th century. The mixture of sperm and egg resulted in progeny that were a blend" of two parents characteristics. Sex cells are known collectively as gametes. According to the blenders, when a black furred animal mates with white furred animal, you would expect all resulting progeny would be gray, a color intermediate between black and white. This is often not the case. Blending theories ignore characteristics skipping a generation. Charles Darwin had to deal with the implications of blending in his theory of evolution. He was forced to recognize blending as not important or at least not the major principle, and suggest that science had not yet got the correct answer. That answer came from a contemporary, Gregor Mendel, although Darwin apparently never knew of Mendel's work.