Slightly more than half of all twins born are male.
In conjoined or Siamese twins, the picture is complicated both by their extreme rarity and by their very low overall survival rate, which is variously given at 5 percent to 25 percent.
Conjoined twins are always identical, because they always come from a single fertilized egg and so are always the same sex. The developing embryo splits within two weeks of conception, but is only partly separated and continues to mature into two infants that are connected to a greater or lesser degree.
Many die at birth and many have severe birth defects. About 35 percent survive just one day. However, historical studies of about 600 sets of conjoined twins over five centuries list more than 70 percent of the surviving pairs as female.
In the United States there has been a sharp rise in multiple births overall, associated with the two overlapping and related trends older age at childbearing and increased used of fertility-enhancing therapies, many of which have multiple pregnancies as a side effect.
Related Posts
-
Do All Siamese Twins Come from Siam?
Siamese twins are twins whose bodies are joined together at birth. Sometimes they are joined only by the skin and can be easily separated. But other times, they share a vital organ, and…
-
How Did Siamese Cats Get Their Name and When Did They First Come to America From Siam?
The Siamese cat is one of the most recognized breeds of Oriental cat. Siamese cats originated in Siam, now known as Thailand, and is also how they got their name. It is believed…
-
Where Do Siamese Cats Come From and Why Are They So Fussy?
If you have ever wondered why Siamese cats are always "talking" or bossing you around, it may be because they are descendants of royalty. Cats were revered in Siam where they were often…
-
When Did Catherine the Great Have Sex With a Horse?
Rumor had it that Catherine the Great accomplished the feat with a special harness. The horse was lowered onto her from above, and that she died when the harness broke and the horse…
-
Which other Primates besides Humans have face to face sex?
Bonobos copulate face-to-face, looking deeply into each other's eyes. This occurs about a third of the time during sexual encounters. Humans once thought that they were unique in engaging in this especially intimate…
-
Which Parent Determines the Sex of Alligator Babies when the Eggs are Laid?
This is sort of strange. Alligators, like many other reptiles, don't have sex chromosomes. As a result, gender isn't determined by the genes of the parents. Instead, whether Mama gator will be blessed…
