[muawiyah]

Since different species of birds express teeth every now and then it's pretty obvious that the tooth gene is still present (even if we haven't developed a full report on the genome), but it's been suppressed in some manner.

One process for suppressing a gene is called "DNA methylation". There may well be others, e.g. a demiurge from the quantum processor in each cell ~ something like that ~ we just don't know yet.

No change in the genome is required for birds to NOT express teeth, nor is a change in the genome required for birds to express teeth.

Mammals somehow suppress the growth of extra tooth sets ~ reptiles have no such problem. Neither do birds. There's work afoot to determine how we can remove the suppression ~ and thereby eliminate dentistry.

[Physicist]

One process for suppressing a gene is called "DNA methylation".

All well and good. But why does that happen in modern birds when it didn't happen in ancient birds?