Beak Careful: Variation May Be Non-Darwinian
Finch beaks loom large in classical Darwinian theory, but two examples of mouth parts in very different animals show that dramatic variations can be achieved quickly without the slow and gradual accumulation of small changes Darwin envisaged.
A. Pufferfish: The pufferfish that can quickly inflate themselves into spheres have a mouth that is unique among teleost fishes: it looks like a parrot’s beak. A paper in PNAS1 claimed that their unusual dentition most likely arose through a regulatory modification during embryonic development:
Teleost fishes comprise approximately half of all living vertebrates. The extreme range of diversity in teleosts is remarkable, especially, extensive morphological variation in their jaws and dentition. Some of the most unusual dentitions are found among members of the highly derived teleost order Tetraodontiformes, which includes triggerfishes, boxfishes, ocean sunfishes, and pufferfishes. Adult pufferfishes (Tetraodontidae) exhibit a distinctive parrot-like beaked jaw, forming a cutting edge, unlike in any other group of teleosts. Here we show that despite novelty in the structure and development of this “beak,” it is initiated by formation of separate first-generation teeth that line the embryonic pufferfish jaw, with timing of development and gene expression patterns conserved from the last common ancestor of osteichthyans. Most of these first-generation larval teeth are lost in development. Continuous tooth replacement proceeds in only four parasymphyseal teeth, as sequentially stacked, multigenerational, jaw-length dentine bands, before development of the functional beak. These data suggest that dental novelties, such as the pufferfish beak, can develop later in ontogeny through modified continuous tooth addition and replacement. We conclude that even highly derived morphological structures like the pufferfish beak form via a conserved developmental bauplan capable of modification during ontogeny by subtle respecification of the developmental module.
Science Daily printed a summary of the paper with a picture of a pufferfish. It said that pufferfish tooth development is “unchanged through evolution” and uses a “highly conserved process” in its beak development. The unique structure represents an adaptation of pre-existing tools: “It is an example of re-specification of its genetic tool-kit for tooth development toward a very alternative, and unique, dentition.”
B. Madagascar birds: Move over, Darwin finches: the vangas of Madagascar show more diversity than the Galapagos birds Darwin made famous. The seed-eating vangas show wide variation in body size, feeding habit, beak shape and size, and coloration. Science Daily showed a vanga family tree of 22 species inhabiting the island that “differ considerably in terms of morphology and resulting foraging habits.” How did these differences arise? Not the way Darwinians thought, the article surprised readers. “Until now, Madagascan vangas were also viewed to be a textbook example of this process” – the rapid filling of vacant ecological niches.
The new idea is that vangas underwent two bursts of rapid diversification separated by long periods of stasis: the first when the birds arrived, the second when a “key morphological innovation” emerged among some of them much later – a sickle-shaped bill that “enabled the new species to retrieve insects hidden under the bark of trees, and so occupy a new dietary niche.” At first glance, this sounds like two Darwin wins instead of one. The last paragraph, however, casts doubt on what is known in even textbook cases of Darwinian evolution:
The fundamental study by the international team indicates for the first time that the amazing diversity of the vangas evolved in a two-step process. The study also illustrates how much of Madagascar and its unusual biodiversity is still not fully understood, and what exciting scientific discoveries may await there. Furthermore, the study shows that a morphological key innovation and related new foraging strategy may result in a burst of speciation, even after the group has already reached its ecological limit. Previously, researchers had thought this to be possible, but it had never been demonstrated. However, the high specialization of the vangas might now be their doom: the habitat to which the birds have adapted over the past 25 million years is shrinking quickly as a consequence of land use and climate change.
The subtitle of that paragraph was, “First evidence for old ideas.” Did they really mean to imply that there has been no evidence for a Darwinian idea for 153 years? The new story, being told by an international team that studied the vangas, is that a founder population arrived 25 million years ago, quickly diversified and reached an ecological limit, and stopped evolving. Then, a key “innovation” just “emerged” 15 million years later, and the birds – that had been living without evolving all that time – underwent another rapid burst of diversification with the new sickle-shaped beaks (until humans started threatening them with “land use and climate change”). The abstract of the original paper in PNAS chirped,2 “Morphological space bears a close relationship to diet, substrate use, and foraging movements, and thus our results demonstrate the great extent of the evolutionary diversification of the Madagascan vangas.”
Science Daily did not explain how the sickle-shaped beak “emerged,” how the male with the sickle beak found a female with the same innovation to pass it on, how the birds learned to use it and develop a taste for new food, why the prey did not evolve counter-measures, how the beak shape correlated with color changes, or why innovations were so rare as to keep Darwin’s theory in check for millions of years at a time. The original paper also stated, “Why some lineages undergo adaptive radiation is not well-understood, but filling unoccupied ecological space appears to be a common feature.”
C. Hopelessness: PLoS Biology3 shared a paper that underscored how difficult it is to confirm a case of adaptive evolution in an ecological community:
Understanding how natural selection drives evolution is a key challenge in evolutionary biology. Most studies of adaptation focus on how a single environmental factor, such as increased temperature, affects evolution within a single species. The biological relevance of these experiments is limited because nature is infinitely more complex. Most species are embedded within communities containing many species that interact with one another and the physical environment. To understand the evolutionary significance of such ecological complexity, experiments must test the evolutionary impact of interactions among multiple species during adaptation.
The authors suggested a method for isolating evolutionary effects from the tangle of infinite complexity in the real world, but could only offer hope for the future. “If evolutionary biology is to become a predictive science,” they concluded (implying it is not yet a predictive science), “future research needs to embrace the complexity inherent to communities and ecosystems.” They even stated that previous studies are misleading: “In this regard it will be important to move beyond studying static patterns of trait variation and selection that are currently employed, which can provide a misleading snap-shot of evolution.” Perhaps the pufferfish and vanga beak studies come to mind, warning evolutionists to be careful when speaking about freak beaks or diversification peaks.
1. Fraser et al, “Replacing the first-generation dentition in pufferfish with a unique beak,” PNAS May 7, 2012, doi: 10.1073/pnas.1119635109 PNAS May 7, 2012.
2. Jønsson et al, “Ecological and evolutionary determinants for the adaptive radiation of the Madagascan vangas,” PNAS April 13, 2012, doi: 10.1073/pnas.1115835109 PNAS April 24, 2012 vol. 109 no. 17 6620-6625.
3. Turcotte MM, Corrin MSC, Johnson MTJ (2012) Adaptive Evolution in Ecological Communities. PLoS Biol 10(5): e1001332. doi:10.1371/journal.pbio.1001332.
Birds are real, pufferfish are real, but “evolutionary understanding” (an oxymoron) is a flight of fancy. Design biologists have explanations, too; they put the capacity for adaptation in the design of the organism, not in the ability of the environment to make lucky adaptations emerge, or in the Stuff Happens Law to create key innovations by chance. How did the Darwin charlatans ever gain such power and control over the journals and media? How can their hegemony be hedged? Maybe the environment will take care of it. Maybe land use and climate change will threaten the Darwinists’ ecological niche, too. A niche in time saves design.