The trap does not work until all the parts were there. The system itself doesn't work until you fit all of them together.

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 find the idea of common descent (that all organisms share a common ancestor) fairly convincing, and have no particular reason to doubt it.

It was a shock to people of the nineteenth century when they discovered, from observations science had made, that many features of the biological world could be ascribed to the elegant principle of natural selection.

For example, both humans and chimps have a broken copy of a gene that in other mammals helps make vitamin C. ... It's hard to imagine how there could be stronger evidence for common ancestry of chimps and humans. ... Despite some remaining puzzles, there's no reason to doubt that Darwin had this point right, that all creatures on earth are biological relatives.

Skin is made in large measure of a protein called collagen.

In order to say that some function is understood, every relevant step in the process must be elucidated.