Years ago I read an article titled "Our genes are not us" (something like that) that touched on the problem of cloning a wooly mammoth. As I understand it, the

Years ago I read an article titled "Our genes are not us" (something like that) that touched on the problem of cloning a wooly mammoth. As I understand it, the problem is that the same genes can produce a different result. An example of this is the caterpillar and the butterfly - same genes but different expression. External factors can change how the genes are expressed. External factors include when and how long the fetus is exposed to certain chemicals in utero.