Can You Shrink a Dinosaur to Make a Bird?
A new research paper claims that birds emerged from a long process of dinosaur miniaturization. The news media loved it.
With all the authority of the American Association for the Advancement of Science, in its premiere publication Science Magazine, Michael J. Benton proclaimed a treatise on “How Birds Became Birds.” Not How Birds Might Have Become Birds, nor How Some Scientists Believe They Became Birds, but How Birds Became Birds. For his unquestionable authority, he had only to lean on his esteemed scientist colleagues from Australia, Italy, and Hungary for support. They published a definitive paper (at least definitive to reporters and evolutionists), “Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds.” In short, the dinosaur line that led to birds began a long 50-million year process of shrinkage. When the asteroid whacked the big guys, the little guys had a survival advantage and flew off.
This was such wonderful news (coming from scientists, after all), the reporters cranked out their headlines:
- “Shrinking dinosaurs evolved into flying birds” (Science Daily)
- “Shrinking Dinosaurs Evolved into Flying Birds” (Live Science)
- “Dinosaurs ‘shrank’ regularly to become birds” (BBC News)
- “Dinosaurs shrank for 50 million years to become birds” (New Scientist)
- “Take a T-Rex and a chicken and you’ll see how dinosaurs shrank, survived and evolved into birds” (Stephen Brusatte in The Conversation)
A Google search on Science Daily’s headline produces 34,000 hits, showing that the article was replicated around the world in short order. Such is the nature of science news these days; replication, not critical analysis. A moment’s philosophical reflection uncovers a weakness in the hypothesis: if miniaturization is the key to survival, why did dinosaurs grow so large in the first place? That’s just one conundrum to chew on for starters. Lead author Mike Lee whisked it away with a just-so story: “birds out-shrank and out-evolved their dinosaurian ancestors, surviving where their larger, less-evolvable relatives could not.” If that is a law of nature, it didn’t work for a lot of other lineages that grew larger over time. Like evolutionary biologist Austin Hughes said (The New Atlantis, Fall 2012), “These invocations of evolution also highlight another common misuse of evolutionary ideas: namely, the idea that some trait must have evolved merely because we can imagine a scenario under which possession of that trait would have been advantageous to fitness.”
There’s no question that Lee, Cau, Naish and Dyke spent some time doing some work. Benton describes it:
The study is based on analysis of an enormous data set and uses sophisticated analytical tools. The authors looked at 120 species of theropod dinosaurs and early birds, coded for 1549 skeletal characters (a data matrix comprising 185,880 cells), and calculated the best-fitting phylogenetic tree while also exploring evolutionary rates.
While impressive, the history of science is littered with much longer and more tedious studies that tended to support alchemy or geocentrism. Since numbers can distract as much as reveal, critical onlookers should be asking if the analysis was rigged to support a pre-existing theory. We see in the Supplementary Information some of the judgment calls the authors made as they chose one piece of software (BEAST) to do their analysis instead of others (parsimony, MrBayes):
Simultaneous estimation of evolutionary rates, topology and divergence dates is now a standard practice in molecular phylogenetics and has been argued to superior [sic] at identifying global optima that best fit all relevant parameters (e.g. 26). In the current context, it should be noted that this approach yields conservative estimates of rate changes, by attempting to dampen extreme rates via changes in branch lengths or topology. In particular, the need to infer implausibly fast rates in sections of the tree could be removed either by minor stretching of very short branches (which barely affects overall tree shape), or by accepting a marginally inferior tree topology that is much more stratigraphically consistent (and which cannot be rejected by topology tests). In contrast, fixing topology and divergence dates before calculating rates will often retrieve extremely short branches with implausibly fast rates (at an extreme, zero – length branches with infinitely fast rates: e.g. 39). Hence, simultaneous analysis of rates and tree shape results in lower (ie conservative) estimates of rate variability than sequential analysis (e.g. 40).
Without getting into the weeds, the object of all these software kits is to force data into phylogenetic trees (evolutionary trees) by one means or another. They are all predicated on the belief that dinosaurs evolved into birds. They all assume the millions-of-years dates. For the authors, choosing which off-the-shelf software did a “better” job (at least by today’s standards) required numerous subjective judgment calls, like deciding which kit required the least amount of apparent tweaking to make a pleasing tree (such as speeding up evolutionary rates on some branches and slowing them down on others, to make a nicer-looking fit). The authors say that the kind of analysis they did is “standard practice in molecular phylogenetics” now, implying that it was not in the past; would previous scientists have been justified in their different practices, if they got different results? Will standard practice change in the future and find this analysis to be flawed? Since none of their analytical methods can be justified objectively, the authors have only produced a result they “like” at this time. It is way beyond the pale, therefore, for Benton to pretend to explain “How birds became birds.”
In addition, despite the impressive statistics about 1549 skeletal characters from 120 species binned into 185,880 cells, skeletons alone imply nothing about change over time without accurate dating of the fossils. The dates, however, are often inferred from the strata in which they are found, which in turn depend on their assumed evolutionary dates (circular reasoning). Even if those ambiguities could somehow be minimized, no species represents a pinpoint in time. To place them in a time sequence, the evolutionists would have to know when each species first appeared, how long it thrived, and when it went extinct. Undoubtedly, many of the 120 species used in the analysis overlapped in time. More ambiguities could result from where the fossils came from; ones that appear ancestral may have been contemporaries from opposite sides of the globe, while others thought to be related may have lived too far apart for any ancestral relationship. And how many of the skeletons truly represent different species? Recently, some dinosaurs thought to be separate species were just juveniles of the same species.
Benton did admit to a lot of subjectivity. He even confessed that this analysis is not the last word on the subject:
Rates of innovation along the bird stem are potentially inflated by oversampling of characters on this lineage (by avian-centric researchers). However, there are three reasons suggesting that the strong rate patterns found here are at least partly real. First, the primary data set (data set 1) attempted to avoid ascertainment bias by explicitly sampling characters across all branches of the theropod tree (including autapomorphies and invariant traits—not sampled in any previous studies). Second, data set 2 was largely constructed to infer relationships among alvarezsaurs and thus likely oversampled characters (and overestimated rates) within this relatively minor “side” clade, yet nearly all the fastest branches in data set 2 are on the bird stem. Third, Bayesian approaches “dampen” perceived rate heterogeneity by smoothing these patterns when (co)sampling topologies and branch lengths and are thus more conservative in this respect than traditional sequential approaches. Ultimately, the potential effects of character oversampling will best be addressed by independent studies, each aiming to explicitly sample all characters—including autapomorphies and invariant characters—in similar fashion to the collection of molecular sequence data.
So despite the beautiful graphs and line-ups of creatures as seen in the BBC article and elsewhere, including the embedded video with the enchanting music, the triumphant headlines camouflaged a great deal of subjectivity, not the least of which was the complete absence of consideration that birds might have been intelligently designed.
Evolution is a self-reinforcing belief system trapped in an echo chamber, where everyone parties on Darwine all day and night.
Exercise: Take Stephen Brusatte‘s headline and finish it with a story of your own: “Take a T-Rex and a chicken and…” It’s OK to have fun; that’s the whole point.