What's a Missing Link

When you contemplate the picture of of 'human evolution' depicted by the 4-6 (depending on the image) characeters in single file (ranging from an ape  to a current human)

you are told by this image that there are missing links that caused this transformation.

So, what are missing links?

And do they really exist?

The link today (pun not intended) will explain the missing links --

HERE'S THE LINK to What's a missing link