Scientific Method / Science & Exploration

The “Ida” fossil: on missing links and media circuses

The immediate casualty of the media hype surrounding a new primate fossil is …

Is it safe to write about Darwinius masillae yet? It has been about a week since news first started leaking out about a fossil that some were calling a "missing link." Last week saw a dramatic unveiling at a press conference, and the arguing hasn't abated since.

About the only thing everyone can agree on is that the fossil that was unveiled last week is spectacular, a complete skeleton of an early primate that even preserved its last meal. As things stand, however, the scientific arguments are beginning to make it look like this episode could be called "Return of the Hobbits." Even though the hobbits, Homo Floresiensis are tens of millions of years removed from the newly described primate, the scientific debates over their meaning seem likely to follow similar trajectories. 

It's probably worth spending some time clarifying what Darwinius isn't. Some of the sponsors of its unveiling, including the BBC and History Channel, would have you believe that the fossil, nicknamed Ida, is a key missing link—one that (in words that have been since been edited out of a phenomenally stupid post on the TED blog) "validates Darwin." Darwin's proposal that organisms are related by common descent was considered validated over a century ago—at best, Ida could have told us something was wrong with Darwin's idea if it had, to borrow Haldane's phrase, shown up in the Cambrian. Instead, it dates from the Eocene, right where we'd expect an early primate to appear.

The "missing link" language is pretty misleading as well. The phrase, in popular understanding, is typically reserved for something that had a mixture of characteristics of human and non-human primates, and was ancestral to modern humans. We've already got a lot of these fossils, and it's not clear that anything is "missing" there. Those fossils, as well as other evidence, suggests that humans diverged from the rest of the primates about 6 million years ago; Ida dates to 50 million years old, so it's not the missing link as most of the public probably knows it.

Can you have a missing link when nothing's obviously missing?

What Ida may link is the anthropoids, a group of primates that include us humans, and earlier groups of primates that emerged shortly after the origin of the phylogenetic order. But, to be missing, people had to suspect you existed in the first place, and it was far from clear that anyone was counting on Ida to show up.

The problem with studying the origins of groups like the anthropoids—and, indeed, many branches of the mammalian tree—is that mammals were around for tens of millions of years, but underwent a sudden diversification. It was once thought that this diversification occurred right after the dinosaurs went extinct, but now it appears to have taken roughly 10 million years after that extinction for mammals to have experienced their big bang, and some have linked the appearance of new species to periods of dramatic climate change that occurred around the Paleocene-Eocene boundary.

If you look at a phylogenetic tree, you'll see lots of branches in the (relatively) compressed period of a few million years, many of which we only know about from fragmentary remains. Somewhere in this period, the anthropoids branched off from an unknown point in the primate tree, but there are reasonable cases to be made about where that branch should be placed (for a good technical overview, I recommend Brian Switek's blog post). Ida apparently belongs to one of these groups, the adapids, and may have some characteristics that are shared with anthropoids, which would (if accurate) help place that branch on the tree.

The degree to which that makes Ida a missing link, then, depends on a couple of things: whether you expected an adapid-anthropoid link in the first place, and whether you accept that Ida shares significant characteristics of both. For whatever reason, the authors of the research paper on Ida don't perform the sort of quantitative cladistic analysis that tends to advance these sorts of arguments. It's entirely possible that the skeleton, which is described by the authors as "lightly crushed," isn't in sufficient shape to allow a full cladistic workup.

Carl Zimmer has also talked to two primatologists who aren't even convinced that Ida has anything new to bring to the table in terms of traits that weren't previously known to exist in adapids.

So, what is missing? Is it a link? At this point, I'd be highly suspicious of anyone who claimed they knew for sure.

Science in a three-ringed circus

The strangest thing about this all is that the scientists behind the fossil, who appear to be working closely with the folks who are calling Ida "The Link," don't even advance that argument in their publication; in fact, they explicitly disavow it. I'll quote the passage in full, with bolding added: "Note that Darwinius masillae, and adapoids contemporary with early tarsioids, could represent a stem group from which later anthropoid primates evolved, but we are not advocating this here, nor do we consider either Darwinius or adapoids to be anthropoids."

If that's true, what were they doing holding a press conference with people who are calling it a link? Apparently, they were contractually bound to do so. Based on interviews in Seed magazine, anyone who wanted to work on the fossil had to sign contracts and nondisclosure agreements, and a grand unveiling was planned from the start.

It's not unusual to see researchers cooperate with press reports that extrapolate their work beyond what's supported by an underlying paper. But I can't recall an instance where the researchers have cooperated with a public outreach effort that took a position they specifically disavowed in the paper.

The journal that published the paper, PLoS One, bears part of the blame for the overhyped coverage. Carl Zimmer has discovered that PLoS One rushed to prepare the paper for their website after having been informed of the press conference. As a result, nobody who was qualified to provide a second opinion on the fossil had even seen it by the time the first press reports were rolling out. Most journals have a policy to avoid situations like this, as they'll refuse to publish work that the authors release in advance of the journal's publication schedule; PLoS, apparently, does not.

Had PLoS put its foot down, some of the worst of the problems could have been avoided. Even if the press conference had gone ahead, if it were accompanied by the journal announcing that the paper would not be published, the public would have at least been aware that the presentation was contentious.

Long term damage

There's clearly a lot of blame to go around here—the media companies that are selling unjustified hype, the scientists and journals that have enabled them—but is there really a problem? After all, interpretations aside, Ida truly is a spectacular fossil, and it dates from an interesting period of primate evolution that's often ignored. What's wrong with grabbing the public's attention with it?

The issue as I see it is that the precise position of Ida in the phylogenetic tree is likely to be the subject of ongoing debates that may rage for years; witness again the Hobbits, which are still spawning Nature papers and press coverage, even without Ida's book deal. And, given the high profile of the initial announcement, any contradictory interpretations will likely reach the news, as well. What message will the public take home from that?

It's impossible to know, but I'd forgive the public if the received message were any one of the following: that scientists don't know what they're talking about, that they'll say anything if it will get them into the news, or that they will skew the facts in order to cut a film deal.

None of those are helpful messages, especially when the subject is evolution, which the public already has unfounded issues with. More disturbingly, similar accusations are precisely the sort that are already being unjustifiably thrown at scientists that perform valuable work in fields like climatology and vaccine development. The treatment of Ida may wind up undermining science in a variety of ways.

PLoS one, 2009. DOI: 10.1371/journal.pone.0005723

Listing image by PLoS one

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