Today's Lesson: There is no such thing as a "Missing Link"

A "favorite" term of many who would deny evolution is to ask about "missing links".  This is a red herring.  There is no such thing.  It's like looking at a vast river or ocean, and asking someone to pick out the one drop of water that started it.  It just doesn't make sense.  Of course, with the information coming out about the Denisovans, I'm sure scientifically illiterate buffoons will spout off in the media.

I am reposting an article from Greg Laden about this (of ScienceBlogs).  He has quite a few things to say about the issue.

Falsehood: Is it ever OK to use the term "Missing Link"?

Today's falsehood¹ is the idea of "The Missing Link." You've heard about The Missing Link. You'll hear that some palaeontologist has discovered something and they tell us it is "The Missing Link." Often, it is a supposed "link" between some ancestor of humans (a fossil ape, a monkey, whatever) and us humans. And often, you'll also find that when the press reports a "missing link" the science blogosphere erupts with a torrent flowing over the phrase and the concept, about how there really is no such thing as "The Missing Link," or that this particular report of such a link is spurious, or something else bad.

This is one of the great things about the blogosphere. In the old days, reporters would use terms or phrases that were inaccurate, misleading, or otherwise annoying and the rest of us ... the scientists and others with direct interest ... would cringe. If teaching a class at that moment, we might have ranted to our students about how we don't like the term or phrase. But today, with the blogosphere up and running in all its glory, we find a totally new phenomenon: The mis-users of terminology get very publicly raked across the coals like so many burning marshmallows. Bwahahaha!!!

This can be powerful and it can be real. For instance, last year, a new and very cool fossil (a new genus, Darwinus) was discovered and called a "missing link." The blogosphere went nuts, and the finders and reporters of Darwinus got totally raked like marshmallows over the coals. Around the same time, a hominid-related research project was reported with the term "missing link" used in a way that fostered a certain degree of blogspheric ire, and again, there was raking. So, when more recently a fossil that in any reasonable person's view could actually be called a missing link was reported, nobody used the term "missing link." Too much bad blood ... marshmallow blood ... had been spilled over the term. No one was going near it this time.

And that, of course, got me thinking. Was there now a consensus that the term "missing link" was always wrong, always incorrect, that there was no such thing as a missing link, and that using the term did little other than making it clear that they ... the users of the phrase ... are stupid marshmallows? I knew this could not be entirely true. I knew this was wrong partly because I have seen the term "Missing Link" used correctly, and I understood it to have a potentially accurate, if somewhat fluffy and not critically important, meaning. Well, the meaning is critically important but using this phrase to represent that meaning may not be important. I also knew something was up because during this last round of missing link bashing some very smart and well educated people were saying things about the concept that were partly true and partly incorrect. They were throwing the marshmallow out with the ashes, as it were. And during the course of this discourse, it dawned on me that "[Fill in the blank] is the missing link!" and "There is no such thing as the missing link!" are BOTH falsehoods. And when that happens, I go to work, because I write about falsehoods and stuff.

The term "Missing Link" is actually central to evolutionary thinking, and Darwin referred to the concept, although often using different words ("intermediate link" for example). "Linking forms" both interested and vexed Darwin. If enough intermediate links could be found between two established species, were they really different species? If evolution proceeds by tiny incremental changes, why does the fossil record not display the intermediate links? He addressed these questions with a number of suppositions, but we now understand that the rate of physical evolution is often variable, with very little visible change occurring for long periods, and rapid change occurring for short periods, and thus difficult to see in the fossil record.

Evolutionary stories are often about adaptive change over time, in which a feature changes in its function, or a new feature emerges. These stories were addressed by Darwin using a combination of fossil evidence, biogeography and comparison of modern species, and information from development (later, DNA would be added as a primary source of evidence). But sometimes, there was a step that must have occurred but that was not indicated by any of these lines of evidence. There would be a species, extinct or not yet discovered, that filled the gap in the sequence of events. These were not always actual historical events, but often simply a sequence of variants that demonstrated the possible modes of transition from one form to another.

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