How do siamese/conjoined twins come about?

Question

How do siamese/conjoined twins come about?

Answer 1

Two contradicting theories exist to explain the origins of conjoined twins. The older and most generally accepted theory is fission, in which the fertilized egg splits partially. The second theory is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together.

Answer 2

okay when twins come to be the egg splits. in conjoined twins, the sperm reaches the egg but the egg does not spilt.

Answer 3

it is where the egg does not fully split when the sperm meets the egg...and where ever the egg is attatched that part of the babies bodies will be attached

Answer 4

It's what happens when an egg tries to split (for identical twins) and never fully splits itself into 2 eggs.