[jec41]

Schwartz concludes, “we can appreciate why ‘missing links’ are so elusive in the fossil record. They probably did not exist.”

Its possible that many may not exist. If one engages in interbreeding or incest and the offspring arrives with six fingers there is no missing link between offspring and parent but the change is evident.

[AndrewC]

If one engages in interbreeding or incest and the offspring arrives with six fingers there is no missing link between offspring and parent but the change is evident.

Well, I suppose one can consider that situation as equivalent to a thalidomide baby. The offspring is not a new species. I think "missing link" is meant in that context.