Science Literature

The blogosphere seems to have realised that there is more hype than substance about the alleged status of Darwinius masillae. In itself, this is reassuring. Providing critical thought about the claims is not just the province of Darwin-doubters. For a selection of relevant links, try ScienceNOW, The Times, Livescience and Ergo Sum Daniel. An overview of the hype is elsewhere on the ARN site, Nature published some quotes that illustrate the "frenzy", and an Editorial in Nature refers to the media communicating a "drastic misrepresentation" of the significance of Ida and what the research team actually claim in their research paper. My interest in adding some thoughts is to tease out some of the scientific issues stimulated by the fossil find.

Ida under the spotlight (Credit: Tyler Lang, Source here)

Today, lemurs are found only on Madagascar and the neighbouring Comores Islands. Fossil lemurs are known: although Madagascar is the dominant source. A significant find in the year 2001, dated at 30 Ma (which makes it earlier than all the African lemurs), comes from Pakistan. This raised questions about whether lemurs originated in Asia rather than Africa. The Messel Pit in Germany has yielded eight fragmentary specimens of primates. A lemur-like species named Godinotia is one of these. Ida is recognisably a fossil lemur and she also comes from the Messel Pit. This confirms that questions need to be asked about the past geographical spread of these animals and also suggests that the model of the lemur ancestors being marooned on Madagascar with subsequent diversification is over-simplistic.

The term "missing link" has been used to publicise the fossil find. The term has fallen out of favour because Darwinists are committed to gradualism, and it follows that every fossil represents a link in the chain from an ancestral form to descendants. For them, it is misleading to refer to one particular fossil as a transitional form because every fosil is transitional in some sense. Advocates of Punctuated Equilibria reject this. They consider species to have a distinct identity: they are born, they live, they die (extinctions). Within their paradigm, it is reasonable to talk about forms that are transitional between one distinct species and another.

To get an evolutionary perspective on human ancestors, we can turn to Richard Dawkins' book The Ancestor's Tale. In a pilgrimage back in time, Dawkins leads his readers to rendezvous with human ancestors. He traces the phylogeny back through the apes and, at Rendezvous 5 about 25 Ma ago, we meet the common ancestor of apes and Old World monkeys. Going back further, at Rendezvous 6 about 40 Ma ago, the apes/Old World monkeys branch meets the New World monkeys branch. Going back further, at Rendezvous 7 which Dawkins puts at 58 Ma ago, the apes/monkeys (anthropoid) branch meets the tarsiers branch. It is only at Rendezvous 8 (associated with a date of 63 Ma) that we reach the ancestor of all primates. The two branches here are the haplorhine primates (apes/monkeys/tarsiers) and strepsirhine primates (mostly lemurs). It is this ancestral "link" that the researchers are claiming to have found: the common ancestor of all primates, including humans. (Note the mismatch on time - Ida is dated as 47 Ma).

The media hype passed lightly over these technical details: the headlines say the missing link is ancestral to humans! When asked about the mismatch between the technical paper and the media headlines, lead author Hurum said:

"I don't think a discussion of Haplorhines [tarsiers, apes, monkeys and humans] and Strepsirhines [the suborder of primates comprising lemurs and lorises] would be easy in popular science. You need to simplify it down to more understandable words. Of course in that you lose a little bit of the scientific terms, but really I think the message is very, very much the same in what we are doing popularly and scientifically."

The claim of the researchers is that the newly described fossil is not just another fossil lemur, but an animal that is ancestral to both lemurs and haplorhines. This requires a redrawing of the family tree and it conflicts with the thinking of numerous other researchers in the field. Norman MacLeod and Angela Milner make some interesting comments about the structure needed for a convincing argument:

"So is Ida another of these great "missing links"? Perhaps - but there is a problem. In order to be recognised as a true ancestor, a fossil must have no truly unique aspects: it must have passed all of its characteristics on to its daughter species, albeit in an altered form. [. . .] On this qualification, the Tiktaalik and Archaeopteryx both fall down as true missing links: both have unique features that have not been passed on to any living creatures. In other words, despite their enormous importance, they are not true ancestors, but belong to small branches of the tree of life whose form is close to that of the true ancestor.
Is the same true of Ida? Well, her fossil's status as a missing link is controversial in a slightly different way. Ida lacks some of the features common to modern lemurs, but does not appear to possess any features unique to our own lineage of anthropoid primates. This renders Ida's evolutionary status ambiguous, at best."

Further technical discussion is provided by Brian Switek, and his points are picked up and endorsed by many others.

"The bottom line is that the hypothesis that Darwinius is closer to anthropoids than tarsiers or omomyids does not have strong support. Even though the authors of the paper constructed a very simple cladogram they did not undertake a full, rigorous cladistic analysis to support their claims. I am baffled as to how they could stress the significance of this fossil without undertaking the requisite research to support their hypothesis.
Is Darwinius important to understanding primate evolution? Of course! It is an exceptionally preserved specimen that could do much to aid our understanding of adapid evolution and paleobiology. The grand claims about it being our ancestor, though, cannot be upheld as true. The researchers simply did not do the work to support their case."

Hurum was asked about what it would take to persuade other palaeontologists that he is right, and Hurum commented that work is in progress that will convince them. This illustrates the problem with creating a media frenzy. The editorial in Nature suggests that a "hyped-up fossil find highlights the potential dangers of publicity machines". Darwin sceptics are accustomed to such media manipulation. The headlines proclaim the advance in evolutionary understanding, but with the passing of time, the significance of the find decreases exponentially. We may yet find that this superbly preserved fossil lemur is within the range of variation observed in living and fossil lemurs and is more suited to provide evidence of stasis within the lemur basic type.

Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology.
Franzen JL, Gingerich PD, Habersetzer J, Hurum JH, von Koenigswald W, Smith, B.H.
PLoS ONE, 2009, 4(5): e5723 | doi:10.1371/journal.pone.0005723

From the Abstract: Darwinius masillae represents the most complete fossil primate ever found, including both skeleton, soft body outline and contents of the digestive tract. Study of all these features allows a fairly complete reconstruction of life history, locomotion, and diet. Any future study of Eocene-Oligocene primates should benefit from information preserved in the Darwinius holotype. Of particular importance to phylogenetic studies, the absence of a toilet claw and a toothcomb demonstrates that Darwinius masillae is not simply a fossil lemur, but part of a larger group of primates, Adapoidea, representative of the early haplorhine diversification.

See also:

Media frenzy, Editorial, Nature 459, 484 (28 May 2009) | doi:10.1038/459484a

So could Ida be the true missing link? By Norman MacLeod and Angela Milner, The Daily Telegraph, 26 May 2009

Poor, poor Ida, Or: "Overselling an Adapid", by Brian Switek, Laelaps (blog), May 19, 2009