Sandy I am talking out of my bounds of knowledge here and expect to get slammed for it but here we go, the Earth has not always been as it is conditions present in the past are not here today, things like temperature, gas ratios in the atmos, salt in the sea etc, has not always been constant, infact travel back 2 billion years and you would suffer, the conditions that lead to this glorious array of life are ever changing, these single cells came into being on an Earth you and I would not recognise.
These extreme changes in the environment combined with bombardment from space over the millions of years have led all creatures from single cell to triceratops to sharks to daffodils to either adapt or die,
Billions of years in such circumstances would it not be a miracle if we did not have this variety.
We would have this variety or nothing atall, everything would not have adapted and died.
I await being jumped upon but in my child with a box of crayons kind of way i know im in the right ball park, if things are not happening in a constant its because the world is not constant, and as the next super volcano errupts you will see what I mean.