User blog comment:Oknight/Superboy and Superman/@comment-1747822-20110314055727/@comment-3465526-20110328193733

Fraternal twins are not identical -- they result from two separate eggs being fertilized by two different sperms -- my mother was a half-identical twin -- her mother produced double eggs each half of which was fertilized by a different sperm. Identical twins develop from a single "conception" where sperm and egg develops to embryo and due to confusion the cells of the embryo split and organize to grow into two complete people.

The phenomenon of identical twins being separated by time is much more common now due to in-vitro fertilization. Many embryos are created, sometimes divided to make more copies (embryos are like starfish -- part will regenerate into a whole) and then frozen for later use. If two split embryos are frozen, they can both be grown to babies years apart, in which case they are still identical twin siblings.