Russell mentions that a body replaces itself physically every seven years in the January 1915 Watch Tower [R5612 : pages, 20, 21].
He even makes reference again to the "convolutions of the brain"
THE RESURRECTION OF THE BODY
The restoration of the bodies of the billions who have died would be a very absurd proposition. Scientists tell us that the human frame changes once in every seven years; that continually old matter is being replaced with new, so that a man who has reached the age of forty-nine years has had seven bodies during his lifetime. The change of the body did not affect the personality of the man, however. The sloughing off of a hand or a foot or the loss of an eye might have taken place, but the human soul continues; for it is this intelligent human being that has resulted from the union of matter and vitality. God's proposition is the restoration of this soul, this personality. Never does He speak of the resurrection of the body.
The theory of the resurrection of the body has involved theologians in many difficulties. Some years ago a story went the rounds of the newspapers to the effect that the coffin of a man who had been buried at the foot of an apple tree had been unearthed, and the discovery made that the roots of the tree had penetrated the coffin and absorbed the body, and that at these roots there was something resembling a hand, an arm, a human limb, etc. In other words, the tree had been living upon that human body. The apples from that tree had been sold to various persons and shipped in all directions; some had been fed to hogs, etc. Those who hold to the theory of the resurrection of the body would have a knotty problem to solve in trying to fit their theory to these facts.
There is not one statement in the Bible that declares that the same body that dies is to be brought forth in the resurrection. On the contrary we read, "Thou sowest not that body that shall be, but bare grain, it may chance of wheat or of some other grain; but God giveth it a body as it pleaseth Him." He will have no difficulty in making a body; Divine Power is equal to any emergency. The Sadducees doubted the Power of God.
A STUPENDOUS MIRACLE
We admit that to produce a body with the same convolutions of the brain, the same individuality, the same soul, the same sentient being, is a miracle so great that we cannot conceive of it. Yet it is that very thing which God purposes to do for the whole human family --thousands of millions in number.
One might wonder as to who was the scientist that originally made the "seven years" statement concerning bodily replacement!
There is a critical difference between a body's material being replaced gradually over time and its being replaced "all at once".
I believe that continuity of being is the key concept to the preservation of personal identity that is missing from Russell's explanation.