Conjoined Twins and Parasidic Twins

I am reading a book called Mutants by Armand Marie Leroi about genetic variety and the human body. It discusses many genetic disorders that cause different abnormalities in the structure and function of the body. The book is very interesting and has a great deal of information in it that is both intriguing and educational.

First, Leroi discusses the fact that what separates a mutation from a variant is that a mutation must be both rare and harmful. Every person has genetic variants that distinguish our hair, eye, and skin color. Interestingly enough, the average person has about three mutant genes in them that can cause invisible problems not visible to every day life. Therefore, are we not all mutants in addition to those who merely look different?

One of the discussions in the book is conjoined twins. Leroi sites a famous case of conjoined twins: Ritta and Christina Parodi. He also discusses the issue of deciding whether a conjoined twin is two separate people or not. Does it depend on whether connected babies have two heads, two hearts, two sets of vital organs etcetera. There are many interesting cases of conjoined twinning: Giacomo and Giovanni Batista Tocci, Masha and Dasha Krivoshlyopova, Yvonne and Yvette McCarther, and many more.

Another deformity is the parasitic twin; a live person that has an attached inanimate body.

Another deformity is cyclopia (viewer discretion advised.) This occurs when the frontal lobe of the brain is not able to split in early fetal development. It is, surprisingly, the most common of all brain deformities in humans. It affects 1 out of 16 thousand live births and 1 out of every 200 miscarriages.

This information hints merely at the first three chapters of the book, which goes on extensively on a variety of other topics. Knowing about these mutations and deformities can help us see exactly how lucky we are to have two eyes, one nose, a mouth, two legs and arms etcetera.