Does Physics Drive Evolution?
Some recent evolutionary papers appear to make physical laws not just constraints on natural selection, but guiding hands that build optimal designs.
Hydrodynamics and the perfect transporter: In cell membranes, aquaporins are hourglass-shaped channels that allow water molecules through but block other molecules. Their “remarkable selectivity,” coupled with “optimal permeability,” is admired by biophysicists – so much so that authors of a paper in PNAS about aquaporins [AQPs] remarked, “in a biomimetic perspective, these results provide guidelines to design artificial nanopores with optimal performances.” How, then, did evolution stumble upon such design perfection? “This suggests that the hourglass shape of aquaporins could be the result of a natural selection process toward optimal hydrodynamic transport.” This statement could mean that natural selection found the optimal shape through blind search, but more implicitly that the laws of hydrodynamics lured natural selection toward “excellent water selectivity.” Most of the paper focused on why the geometrical shape is so effective:
The aim of this work was to determine the effect of geometry and BCs [boundary conditions] on hydrodynamic entrance effects in biconical nanochannels. Using FE [finite-element] calculations, we have shown that compared with a plain cylindrical pipe, a biconical channel of optimal angle can provide a spectacular increase in hydrodynamic permeability. A simplified model based on entrance effects and lubrication approximation rationalizes the observed behavior. Although speculative, this could indicate that the hourglass geometry of AQPs results from a shape optimization, to reduce end effects and maximize water permeability.
They said very little about evolution. What they did say amounts to an airy speculation that, somehow, physics drives evolutionary progress:
Among transmembrane proteins, and ionic channels in particular, examples abound where the particular function––ion selectivity, for instance––is tied to a specific feature of the molecular architecture. However, it remains worth wondering, as we have done here, whether generic factors such as viscous dissipation could be the driving force behind the shapes fine-tuned by evolution.
Fluid dynamics and the perfect lung: More blatant in the assertion that physics drives evolution is a headline on PhysOrg, “How fluid dynamics and transport shaped the structure of our lungs in the course of evolution.” The speculations of two French physicists goes beyond claiming that physics merely constrains evolution, though it overlaps with that notion. It elevates physics to an essential player in the process of design optimization, a voice telling the evolutionary tinkerer, ‘you’re getting warmer’—
In an evolutionary perspective, the size of primitive multi-cellular species was necessarily limited by nutrients’ diffusion speed. One hypothesis defended in this study is that larger primitive animals have thus been conditioned by a progressive Darwinian selection of tree-like ‘space-filling’ nutrient distribution systems. Then, their genetic material was ready to be shared to allow mammalian respiration. Successive inspirations and expirations cycles had to be optimised so that external air could reach the alveoli before expiration starts. This form of evolutionary tinkering, the authors believe, would have allowed the emergence of mammalian respiration—as opposed to fish-style breathing through gills.
With physics in the driver’s seat, it’s no wonder that “the structure of the alveolar system is indeed optimal to allow efficient transport of oxygen from the air to the blood,” the article ends. “This new insight into the lung’s evolutionary process stems from the physical principles underlying the architecture of living systems.”
Evolution is a mystical form of polytheism for modern intellectuals. Any questions? You thought evolution was impersonal and unguided. That would never work. Cryptic spirits animate all of nature.
They even have names. The blind goddess Tinker Bell is helped by Engineer Bill, calling out “You’re getting warmer!” as the unholy spirit of Charlie, the Bearded Buddha, smiles down from above, “allowing” endless forms most beautiful to “emerge.” Since these deities are invisible, one needs the shamans to interpret the game, continually offering “new insight” to the peasants, ever stringing them along to keep the funds flowing. The Great Myth must remain a perennial work in progress, lest the shamans run out of business in their temples, the universities. They shudder at the prospect of begging on street corners with signs, “Will tell stories for food.”