The Gecko's Toes
The gecko is one of the icons of biomimetics. That's the science of taking cues from designs in nature to develop and improve our own designs, an approach that is of now widely recognized use in manufacturing a variety of cool new technologies. This adorable lizard with a sideline in auto insurance uses tiny hairs in its toes to make scaling up or down a sheet of vertical glass look like a breeze. Of course whenever you read about stuff like this, researchers and journalists feel the need to vaccinate against any possibility of their being misunderstood as gesturing to intelligent design. Typically, though not always, they are careful to couch the discussion in terms of "natural design."
In the case of geckos, this defensive posture just got even harder to maintain, when you consider what genetic data appear to reveal about their evolution. A weird thing about gecko toes is that this creature has stumbled upon its unique technology any number of times in the course of its history, then lost it, and then stumbled upon it again, independently in independent gecko lineages. PLoS One has the story ("Repeated Origin and Loss of Adhesive Toepads in Geckos"):
Geckos are well known for their extraordinary clinging abilities and many species easily scale vertical or even inverted surfaces. This ability is enabled by a complex digital adhesive mechanism (adhesive toepads) that employs van der Waals based adhesion, augmented by frictional forces. Numerous morphological traits and behaviors have evolved to facilitate deployment of the adhesive mechanism, maximize adhesive force and enable release from the substrate. The complex digital morphologies that result allow geckos to interact with their environment in a novel fashion quite differently from most other lizards. Details of toepad morphology suggest multiple gains and losses of the adhesive mechanism, but lack of a comprehensive phylogeny has hindered efforts to determine how frequently adhesive toepads have been gained and lost. Here we present a multigene phylogeny of geckos, including 107 of 118 recognized genera, and determine that adhesive toepads have been gained and lost multiple times, and remarkably, with approximately equal frequency. The most likely hypothesis suggests that adhesive toepads evolved 11 times and were lost nine times. The overall external morphology of the toepad is strikingly similar in many lineages in which it is independently derived, but lineage-specific differences are evident, particularly regarding internal anatomy, with unique morphological patterns defining each independent derivation.Geckos are hugely diverse, with more than 1450 species. Most but not all (about 60 percent) have the special toes. Going back to the mid-Cretaceous, they have received the gift of this adhesive-toe system -- or "digital design" as the study's authors put it, this "integrated design" as other scientists say who are cited in the article -- when they needed it, based on "design principles," in the words of still other researchers. When their environment changed and the design proved unhelpful, geckos shrugged if off. In a different living environment, they needed again it and, bingo, back it came.
However unlikely it seems to evolve this design even once, geckos, alone in nature, did it 11 times. It's like riding a bike, evidently. Once you've mastered adhesion via van der Waals force, you never really forget.
Image: Kirk Crawford/Flickr.