Written by Mary Roach in 2005, Spook tackles the afterlife from the point of a scientific scholar. She examines the concept of death in relation to what people believe to be true and how people react to certain phenomena. Yet it can be applied to biology because one must have a strong idea of life to recognize death.
Roach tackles many of the concepts that we hold as faith and supernatural such as reincarnation, ethereal beings, and the idea of the soul. The soul is part of life because it is so closely related to how we continue in our world. Without a soul many people believe that we would not be able to go on living, yet it is not something that can be physically seen.
Covering the topic of what is not physically seen, Roach explores the theories of Antoni van Leeuwenhoek, Rene Descartes and Duncan MacDougall. Leeuwenhoek was responsible for a theory that believed that the soul came from a preformed human inside the male sex cell and Descartes studied the anatomy looking for the soul. He was able to find what he believed to be a soul in the pineal gland, which he chose mainly because of its location. MacDougall was the first scientist to spend research time measuring a person before and after death to look for a soul. What he found was the difference of 21 grams between a living and a dead person and this number has become synonymous with a soul's correct ‘mass'.