Wild Neighbors: Woody Has the Last Laugh

By Joe Eaton
Tuesday March 01, 2011 - 10:14:00 PM
Golden-fronted woodpecker: irreducibly complex? via Wikimedia Commons
Golden-fronted woodpecker: irreducibly complex?

A few years back I wrote about the bestowal of the Ig Nobel Prize for medicine on UC-Davis ophthalmology professor Ivan Schwab for his explanation of why woodpeckers don’t get headaches. (Other Ig Nobels have honored studies of the effect of Viagra on jet-lagged hamsters and the fluid dynamics of swimming in syrup.) 

Schwab was following up on the research of the late Philip May of UCLA on the anatomy and physiology of the pileated woodpecker. 

May calculated that a crow-sized pileated is capable of hammering its beak into a tree trunk at a rate of up to 20 times a second 12,000 time a day, with a 1200 g force on each impact, without knocking its brains out. This would be equivalent to hitting a stone wall face first at 16 miles an hour. 

How does it do that? May reported that the pileated woodpecker has a thick skull with spongy cartilage at the base of the beak to absorb the force of the hammer blows. Its upper and lower jaws are attached to the skull by strong muscles that contract a millisecond before each blow, creating further cushioning and diverting the force of the impact to the base and rear of the skull and bypassing the brain. Furthermore, each stroke is perfectly perpendicular to the tree, avoiding torsion that might tear the membrane enclosing the brain or cause concussion. 

Neither Schwab not May saw any potential technological spinoffs from this remarkable product of evolution. Just last month, though, two UC-Berkeley researchers, Sang-Hee Yoon and Sungmin Park, published an article in what is apparently the inaugural issue of the journal Bioinspiration and Biomimetics. Yoon and Park, both with UC’s Department of Bioengineering, used videos and CT scans to analyze the cranial anatomy of the golden-fronted woodpecker, a smaller bird native to Texas, Mexico, and Central America, as a mechanical system. 

They identified four key shock-absorbing structures: a hard but elastic beak: the hyoid, a spring structure that supports the long coiled tongue; an area of spongy bone in the skull; and the way the skull and cerebrospinal fluid interact to suppress vibration. 

Based on that, Yoon and Park built an artifical analogue of a woodpecker’s head, substituting a metal cylinder for the beak, a rubber layer for the hyoid, an aluminum layer for the cerebrospinal fluid, and tiny glass spheres for the spongy bone. Then they packed the whole shebang and some kind of electronic apparatus into a bullet, loaded it in an airgun, and fired it at an aluminum wall. They report that their system protected the embedded electronics from impacts up to 60,000 g. 

So? Well, the best current flight recorders can only withstand 1000 g. More ominously, Yoon told the British magazine New Scientist that “an institute in Korea is now looking into military applications for the technology,” which apparently include bunker-busting bombs. (Let’s hope that’s South Korea; things are bad enough already.) Other possibilities: protecting football players and racecar drivers from brain injuries and spacecraft from meteorite impacts. 

Almost predictably, the creationists have chimed in about the woodpecker’s skull as a perfect biological system that only a divine force could have created. Brian Thomas of the Institute of Creation Research: “The woodpecker has long been considered a living refutation of big-picture evolution…Each feature that Yoon and Park mimicked includes specified material and arrangements, and all four are required for a woodpecker to effectively drill holes into wood…there is no natural way for a whole suite of required, specified features to just ‘get together’ all at one time. Perhaps unwittingly, these University of California researchers corroborated that the only way to achieve all-or-nothing design is by purposeful intent. Thus, the woodpecker is a testament to the superior engineering skill of its Creator.” 

In other words, to paraphrase Darwin’s rhetorical question about either the vertebrate eye or the avian wing: what good is a partial woodpecker? It’s the old irreducible complexity argument. 

As it happens, a number of “partial woodpeckers” have evolved in places that woodpeckers never colonized: Australia, New Zealand, Madagascar, New Caledonia, the Hawaiian and Galapagos Islands. Some are birds, a couple are mammals. Each has occupied the vacant woodpecker niche, evolving the part of the woodpecker tool kit that is required to extract insect larvae from wood. They’ve become, in the words of ornithologist H. Douglas Pratt, “Rube Goldberg woodpeckers.” 

The aye-aye of Madagascar, an aberrant lemur, uses its rodent-like incisor teeth to gnaw wood and an elongated middle finger to harpoon its prey. The Australian striped possum accomplishes the same thing with a modified fourth digit and bayonet-like lower incisors. In a rare Hawai’ian finch called the ‘akiapola’au, the lower mandible of the beak is adapted from drilling into wood and the upper for probing into it. The unfortunately extinct huias of New Zealand had sexually dimorphic beaks: males were excavators, females were probers, and they foraged as a team. And don’t forget the Galapagos woodpecker finch and the New Caledonian crow, both of which make and use tools to get their grubs. 

I can’t think of a better example of evolution as the great tinkerer—or, in the person of Brian Thomas, of the ignorance and arrogance of the creationists.