Given this is a Biblical question why not give a Biblical answer?
For the record, here is a story to illustrate the principle and explain the anomaly:
“Regenerating ribs - Adam and that ‘missing’ rib”
A head-on impact with a fully laden fuel tanker at highway speeds is an experience I would hope for none to share. The surprise was to have survived it.
During the 5 1/2 months in hospital, and for years afterwards, I had a series of operations to reconstruct various parts of me, particularly the bones of my face.
These operations often required using my own bone for grafting. I noticed that the plastic surgeon would keep going back to the right side of my ribcage, through the same horizontal scar, actually, to get more bone for these procedures. One day, I asked him why he hadn’t ‘run out of bone’. He looked at me blankly, and then explained that he and his team took the whole rib out, each time. ‘We leave the periosteum intact, so the rib usually just grows right back again.’
Despite having trained and practised as a family doctor, I was intrigued; I had never realised this before. The periosteum (the literal meaning of this word is ‘around the bone’) is a membrane that covers every bone—it’s the reason you can get things stuck between your teeth while gnawing on a leg of lamb, for instance. The periosteum contains cells that can manufacture new bone. Particularly in young people, ‘rib periosteum has a remarkable ability to regenerate bone, perhaps more so than any other bone’.
Thoracic (chest) surgeons routinely remove ribs, and these often grow back, in whole or in part. A lot depends on the care with which the rib is removed; it needs to be ‘peeled’ out of its periosteum to leave this membrane as intact as possible. A major reason why the rib is the ideal situation for such regeneration is that the attached intercostal muscles provide it with a good blood supply.
When the surgeon originally told me this, my immediate thought was—‘Wow, that’s really neat, Adam didn’t have to walk around with a defect!’ In Genesis 2:21, referring to the creation of Eve, we read:
‘And the LORD God caused a deep sleep to fall on Adam, and he slept. And He took one of his ribs, and closed up the flesh underneath.’
Surprisingly, some Christians have grown up believing that men have one less rib than women. They have the same number, of course.
For years before my accident, when asked about this, I would give a reply something like this:
‘If your father had lost his finger in a circular saw, would you really expect all his children to have one less finger, too? Or all of his sons, but not his daughters? Of course not. The DNA instructions that are passed on from parent to child are in the form of a code, like writing—removing a rib (or finger) would not change the instructions on the code, so all the offspring will have all their ribs (or fingers).’
While all that is still very true and pertinent, this information about rib regrowth adds a new and fascinating dimension. God designed the rib, along with the periosteum. He would certainly have known how to remove the rib in such a way that it would later grow back, just as ribs still do today—without requiring any sort of special miracle.
Adam would not have had any permanent area of weakness in his rib cage, but would have had, for all of the hundreds of years of his life, the same number of ribs that you and I have today.
It does make a kind of sense to use the same frame, and actually would have not required making of any absolutely new DNA, since Adam already had an X chromosome. I guess God subscribes to the theory of working smart, not hard.