Identical twins: The differences explored

We are told (in a Nova program, Ghost in your Genes, October 16, 2007) ,

Scientists have long puzzled over the different fates of identical twins: both have the same genes, yet only one may develop a serious disease like cancer or autism. What's going on? Does something else besides genes determine who we are? In this program, NOVA reveals the clues that have led scientists to a new picture of genetic control and expression. One such clue is the surprisingly modest number of genes that turned up when technology made it possible to map the human genome. The Human Genome Project was originally expected to find at least 100,000 genes defining the human species. Instead the effort yielded only about 20,000—about the same number as in fish or mice—too few, some believe, to account for human complexity. Learn more about the connection between epigenetics, aging, and cancer on the program's companion website.

"What's going on? Does something else besides genes determine who we are?"

Um, yes. Here are three obvious observations right away:

- All we need to know about any life form is not necessarily in its DNA, as the program makes clear. Frustratingly, the true causes and cures of cancer and autism are controversial and clouded.

But our DNA is not a book of magic in which all the answers are written, and it is too bad if anyone thought it was.

- Identical twins may have almost-identical DNA, but usually one is the dominant twin and the other the sub-dominant one. Also, they tend to separate as adults and have different experiences. Over a lifetime, these differences can add up.

- Also, humans are intelligent and make independent choices. Different choices lead to different outcomes. The fact that anyone should doubt this is a symptom of the damage materialism (= you are either a robot or a monkey) has done to science.

See also Identical twins does not mean identical minds

Intelligence: How much is heredity and how much is environment

How much brain do you need?

Hat tip: Stephanie West Allen at Brains on Purpose