As stated earlier, conjoined twins is an incredibly rare occurrence. They appear ranging from 1 in every 50,000 to 1 in every 100,000 pregnancies. 70% are female (although the reason for this is unknown), and 40%–60% result in stillborn births or miscarriages, according to a paper published by the John Burroughs Science Department. The process through which identical twins only partially separate to form conjoined twins is not fully understood, and the infrequency of such cases doesn’t allow for a great deal of scientific study.

There are many different types of conjoined twins depending on what body parts they share, but more often than not, the twins have their own distinct characteristics. Just like Abby and Brittany Hensel, other cases of conjoined twins display individual preferences and personalities, although they may “share thoughts” due to their combined condition. So, while conjoined twins are rare, when we do come across them, it is important to treat them as separate entities, true individuals, not a singular being.

Photo: Jesus Daily

Adding to the assertion that Abby and Brittany, along with other conjoined twins, are two distinct individuals is the fact that it is possible for one of them to fall ill and the other remain healthy. For example, Brittany once had pneumonia while Abby was perfectly fine, and in fact, when Brittany was unable to keep her medicine down, her sister volunteered to take the medicine in the hopes it would still take effect and heal the other sibling. This is an interesting phenomenon considering they share a bloodstream, so when one receives an immunization, for example, the other will benefit as well; if one twin catches a cold, the other should soon follow, but that’s not always the case with Abby and Brittany.

The two underwent three surgeries in their youth, but since then, they have been in excellent health and continue to astonish doctors with their strong vitality.

Photo: Brain Sharper

The “original” conjoined twins whose lives coined the phrase “Siamese twins” were Eng and Chang Bunker. The brothers were born in Siam (now Thailand) in 1811 and miraculously lived to age 63. In 1829, when they were 17, Eng and Chang were taken to America by two men who saw a money-making scheme in the brothers. Setting them up as a freak show, Eng and Chang were treated like slaves while people paid their “owners” admission to see the phenomenon of these conjoined siblings.

After some time, however, the two were able to negotiate their freedom and eventually bought land with their savings in Mount Airy, North Carolina. There, the two ironically bought slaves to work on their farm. Eng and Chang later met and married two sisters and fathered a total of 21 children between the two of them. An autopsy performed after their death in 1874 revealed they shared a liver, which is now on display at the Mutter Museum in Philadelphia, Pennsylvania.

Although Eng and Chang Bunker made “Siamese” twins famous, they were not the first pair of conjoined siblings to be born and survive into adulthood. However, due to the awe and attention such cases inspire, people have taken advantage of this rarity over the years to earn a fast buck, making many people question the reality of conjoined twins before modern medical science proved them true.

One such example of skepticism is the Biddenden Maids, twin sisters born in 1100 in England, supposedly joined at the shoulder and hip. According to legend, when one of the sisters, Mary, died in 1134, the surviving twin, Eliza, refused to try and have her surgically removed, resulting in her death six hours later. Many have doubted this tale, calling it a vulgar story made up to feed the masses. The nature of their conjoining is lacking in substance as well: it is highly unlikely that the sisters would have two separate parts of conjunction and were instead likely to be joined only at the hip, making them pygopagus twins.