Major mutations only happen every ten years or so.

"These mutations or changes have happened before, have they?"

It was previously believed that these mutations happened completely by chance, with no regard for their effects on the organisms.

So if an island was populated entirely by black mice, mutations could happen creating alleles for white fur.

Spontaneous mutations would happen at a frequency vastly larger than observed.

If a mutation happens in the non-gamete forming tissues, it is characterized as somatic.

If enough time passes and enough mutation has happened in theory they may not be able to mate again.

The mutations happen naturally on a single branch of a tree that otherwise grows normally.

If mutations happen randomly, you would expect evolution to work in both directions.

Some words have been around a long time, but semantic mutations happen.