Throughout history there have been many other examples, similar to that of Haeckel, Huxley and the cell, where a key piece of a particular scientific puzzle was beyond the understanding of the age.

Most of the places I've been, I've been a main piece of the puzzle.

In many biological structures proteins are simply components of larger molecular machines.

In Darwin's time all of biology was a black box: not only the cell, or the eye, or digestion, or immunity, but every biological structure and function because, ultimately, no one could explain how biological processes occurred.

I have lived here for so long and this was the last piece of the puzzle.

It's just one piece of the puzzle.