Identical twins were too close; when one of them died, the other died in part with him.
Identical twins—one grows old like other people; the other remains young.
At first glance they looked like carbon copies of each other, although they were no more identical than identical twins ever are.
When this happens twinning results, and the twins are exactly alike, being known as identical twins.
Even at a distance the Terrans looked disturbingly alike, and when they got closer I could see that they were identical twins.
If they exist, why do not ordinary brothers become as much alike as identical twins?
They are identical twins, facing the same environment, sharing the same heredity of blasted chromosomes.
However, there are twins known as identical twins who are remarkably alike and who are always of the same sex.
But there is reason to suppose that identical twins in reality come from the same zygote.