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Hairy Matters for Evolution

Photo: Sea otters seem to enjoy grooming, by "Mike" Michael L. Baird, CC BY 2.0 , via Wikimedia Commons.

Hair is one of the traits that define mammals, but hair-like structures are almost ubiquitous in metazoans. They are found on the furry bodies of honeybees, velvet ants, and hunting spiders. Some plant leaves are fuzzy with hair-like protrusions on the surface. And as we will see, even some individual cells have hair. Any fine, filamentous outgrowth can be called hair. Most commonly we think of mammal hair, made up of “numerous fine, usually cylindrical, keratinous filaments growing from follicles in the skin.” Within Mammalia, hairs can be extremely varied in width, color, density, and texture. Here are some wonders of hair.

Sea Otter Hairs Insulate

In The Scientist, a research team at the Monterey Bay Aquarium tell about their investigation of sea otters. How do these small mammals keep warm without the layer of blubber that whales and sea lions grow under their skin? Part of the answer involves the density of the otter’s specialized fur:

Sea otters are the smallest of the marine mammals, and do not have this thick layer of blubber. Instead, they are insulated by the densest fur of any mammal, with as many as a million hairs per square inch. This fur, however, is high maintenance, requiring regular grooming. About 10 percent of a sea otter’s daily activity involves maintaining the insulating layer of air trapped in their fur. [Emphasis added.]

The animals seem to enjoy this pastime. A million hairs per square inch implies a million hair follicles in the skin, too: each follicle made of specialized cells programmed to manufacture and extrude keratin at the right density, color, and length for the species.

The researchers describe another strategy used by sea otters for warmth. In their muscle cells, the mitochondria “leak” some of the excess energy from ATP production to use as heat. 

We discovered the mitochondria in sea otter muscles could be very leaky, allowing otters to turn up the heat in their muscles without physical activity or shivering. It turns out that sea otter muscle is good at being inefficient. The energy “lost” as heat while turning nutrients into movement allows them to survive the cold.

Inefficiency by design: that’s a specification that works, too. The cost of this strategy is having to eat a lot. To maintain a metabolic rate three times higher than most other mammals, sea otters must consume 20 percent of their body mass in calories each day. If mitochondria could be tuned this way in humans, it might allow us to eat more without gaining weight, the authors point out.

Guard Hairs Act as Heat Sensors

Another hairy matter came up in The Scientist. Amanda Heidt tells about the findings of physicist Ian Baker, who designs infrared sensors for industry. Baker took his work home with him. He scanned the fields and woods around his home in Southampton, England, with infrared cameras, looking for animals. He observed predators like cats and owls crouching behind their noses when hunting. Suspecting they might be trying to conceal their infrared signature from prey, he reasoned that prey animals like mice must be able to sense infrared body heat.

As part of his investigation, Baker put mouse hairs under a microscope, and what he saw looked immediately familiar, he tells the Times. The mouse’s guard hairs — the long, coarse strands that form a protective layer over an animal’s undercoat — looked similar to structures he often saw in his sensors. Specifically, the hairs contained evenly-spaced bands of pigment that, in a sensor, allow the instrument to focus onto specific wavelengths of light.

Measuring the stripes supported the idea that, just as with a thermal camera, the hairs seemingly tuned into the 10-micron wavelength of light, the heat signature given off by many living things. “That was my Eureka moment,” Baker tells the Times.

Cat owners will recognize this change in behavior when their pet, focused on a bird or mouse, crouches low, making its body look as small as possible. There’s a reason for everything. For the balance of nature, predators should have to work for their meal; prey animals need a fighting chance. Similar advantages accrue to moths hunted by bats; they have strategies to sense bat echolocation clicks and use avoidance behaviors.

Baker investigated guard hairs in other animals like rabbits and squirrels. From his physics perspective, he was surprised to find that some species have

even more complex guard hair structures that suggest “really sophisticated optical filtering.” If such hairs can indeed detect heat, it would mean that many species have a 360-degree sensory shield.

He commented that his work shows how many animal secrets remain to be discovered. “There must be a huge amount we don’t understand.” He published his initial findings in the journal Royal Society Open Science with micrographs of the guard hair cells that resemble his designed infrared sensors. Evidently, he felt compelled to say these evolved. “Many types of infrared detectors have evolved in insects, spiders, reptiles and mammals, each following their own design concept,” he said, confusing intelligent design with blind evolution.

Ear Hairs Amplify Sound with Motor Proteins

Some people discover unwanted hairs growing out of our ear lobes occasionally, but there are tinier “filamentous outgrowths” farther inside that we depend on for hearing. These are the “hair cells” inside the cochleae of our inner ears. In particular, the outer hair cells (OHC) anchored along the basilar membrane respond to specific frequencies along the length of the spiral Organ of Corti by flexing and letting ions trigger pulses in the neurons of the auditory nerve. OHCs, therefore, are at the nexus of signal transduction from mechanical energy to electrical energy. But how do they flex?

In a pipe organ, motorized actuators open specific pipes to air flow when the player presses keys. A comparable actuator was suspected in the ear. When prestin (a motor protein) was discovered associated with the OHCs, researchers suspected it was the actuator. It is indeed, and now its mode of action has been determined by researchers at the University of Chicago. They published their results in Nature — see Bavi et al., “The conformational cycle of prestin underlies outer-hair cell electromotility.” Like organ pipe actuators, prestin runs on electricity. 

The voltage-dependent motor protein prestin (also known as SLC26A5) is responsible for the electromotivebehaviour of outer-hair cells and underlies the cochlear amplifier. Knockout or impairment of prestin causes severe hearing loss. Despite the key role of prestin in hearing, the mechanism by which mammalian prestin senses voltage and transduces it into cellular-scale movements (electromotility) is poorly understood. Here we determined the structure of dolphin prestin in six distinct states using single-particle cryo-electron microscopy. Our structural and functional data suggest that prestin adopts a unique and complex set of states, tunable by the identity of bound anions…. Our data suggest that the bound anion together with its coordinating charged residues and helical dipole act as a dynamic voltage sensor. An analysis of all of the anion-dependent conformations reveals how structural rearrangements in the voltage sensor are coupled to conformational transitions at the protein–membrane interface, suggesting a previously undescribed mechanism of area expansion. 

The authors speak of this amazing protein with terms like “a complex set of interrelated conformations” and the “intricate sequence of conformational changes” that it performs. Prestin acts like a physical switch by adopting two conformational shapes that push the channel down or up. It produces lateral forces that directly influence the angle of the outer hair cells and the physical state of the membrane. Remarkably, there are millions of these motors working in concert! The scientists estimate a density of up to 7,000 prestin proteins per square micrometer. And they are fast — as fast as one can hear a rapid riff by a musician. The scientists are not yet sure whether other motor proteins are involved, so this is a story to watch.

One More Hairy Story

Lest we forget, most cells in our bodies have another type of hair — a cilium. Cilia are one of Michael Behe’s examples of irreducible complexity. Primary (non-motile) cilia act like antennas on the cell. Motile cilia sweep away debris in airways and perform other vital functions during development. These hair-like protrusions are built from the inside out with motors carrying parts up motorized trackways, as described here. This makes them even more complex than the hairs in a sea otter’s fur. Meng et al. published in PNAS new ideas about how arrays of motile cilia coordinate their rhythms.

The Closer You Look 

With almost everything in biology, traits become more wondrous the closer you look. Yet evolutionists continuing to attribute these wonders to evolution. “Mammals have evolved a highly sophisticated sense of hearing that is characterized by extraordinary sensitivity and the ability to process high-frequency sounds,” the authors of the prestin paper say. “This evolutionary outcome is the result of a mechanism of amplification that relies on the specialized electromotility of the mammalian outer-hair cells (OHCs).” Why must it be an “evolutionary” outcome? The word contributes nothing.

Bet on this: someday statements like that will seem as unscientific as fairy stories. The rest of us can enjoy and marvel at what observational science is finding. Design scientists and engineers know how to associate effects with necessary and sufficient causes.